The vacuolar serine protease, a cross-reactive allergen from Cladosporium herbarum

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.

Assessing the contributions of phylogenetic and environmental determinants of allergic cosensitization to fungi in humans

BACKGROUND

Understanding how allergies to 1 environmental fungus can lead to cosensitization to related fungi is important for the clinical management of allergies. Cosensitization can be caused by monosensitization combined with antibody cross-reactivity, or by coexposures driving independent sensitizations. A pioneering study showed that patterns of IgE cosensitization among 17 fungal species mirror fungal phylogeny. This could reflect either epitope or habitat similarity. Thanks to an improved understanding of fungal phylogeny, larger serologic testing datasets, and environmental data on household fungi, we can now characterize the relationship between cosensitization, species similarity, and likely coexposure with greater precision.

OBJECTIVE

To assess the degree to which IgE cosensitization in a group of 17 fungi can be attributed to species similarity or environmental coexposure.

METHODS

Cosensitization patterns among 17 fungal species were estimated from a dataset of approximately 8 million serologic tests on 1.6 million patients. Linear regression of cosensitization on phylogenetic distance and imputed coexposure was performed. In addition, branch lengths for the phylogenetic tree were re-estimated on the basis of cosensitization and compared with corresponding phylogenetic branch lengths.

RESULTS

Phylogenetic distance explains much of the observed cosensitization (adjusted r2 = .68, p < .001). Imputed environmental coexposures and test co-ordering patterns do not significantly predict cosensitization. Branch length comparisons between the cosensitization and phylogenetic trees identified several species as less cosensitizing than phylogenetic distance predicts.

CONCLUSION

Combined evidence from clinical IgE testing data on fungi, along with phylogenetic and environmental exposure data, supports the hypothesis that cosensitization is caused primarily by monosensitization plus cross-reactivity, rather than multisensitization. A serologic test result should be interpreted as pointing to a group of related species that include the sensitizing agent rather than as uniquely identifying the agent. The identified patterns of cross-reactivity may help optimize test panel design.

Protease/antiprotease network in allergy: The role of Staphylococcus aureus protease-like proteins

Staphylococcus aureus is being recognized as a major cofactor in atopic diseases such as atopic dermatitis, chronic rhinosinusitis with nasal polyps, and asthma. The understanding of the relationship between S aureus virulence factors and the immune system is continuously improving. Although the precise mechanism of the host's immune response adaptation to the variable secretion profile of S aureus strains continues to be a matter of debate, an increasing number of studies have reported on central effects of S aureus secretome in allergy. In this review, we discuss how colonization of S aureus modulates the innate and adaptive immune response, thereby predisposing the organism to allergic sensitization and disrupting immune tolerance in the airways of patients with asthma and chronic rhinosinusitis with nasal polyps. Next, we provide a critical overview of novel concepts dealing with S aureus in the initiation and persistence of chronic rhinosinusitis with nasal polyps and asthma. The role of the S aureus serine protease-like proteins in the initiation of a type 2 response and the contribution of the IL-33/ST2 signaling axis in allergic responses induced by bacterial allergens are discussed.

Cladosporium species in indoor environments

As part of a worldwide survey of the indoor mycobiota about 520 new Cladosporium isolates from indoor environments mainly collected in China, Europe, New Zealand, North America and South Africa were investigated by using a polyphasic approach to determine their species identity. All Cladosporium species occurring in indoor environments are fully described and illustrated. Fourty-six Cladosporium species are treated of which 16 species are introduced as new. A key for the most common Cladosporium species isolated from indoor environments is provided. Cladosporium halotolerans proved to be the most frequently isolated Cladosporium species indoors.

A critical review on serine protease: Key immune manipulator and pathology mediator

Proteolytic activity is fundamental to survival, so it is not surprising that all living organisms have proteases, especially seine protease. This enzyme in its numerous isoforms and homologues, constitutes the quintessential offence and defence factors, in the form of surface proteins, secreted molecules, gut digestive enzymes, venom in specialised glands or plant latex, among other manifestations. Occurring as trypsin, chymotrypsin, elastase, collagenase, thrombin, subtilisin etc., it mediates a diverse array of functions, including pathological roles as inflammatory, coagulatory to haemorrhagic. This review emphasizes that despite the superficial differences in mechanisms, most health issues, be they infectious, allergic, metabolic, or neural have a common conduit. This enzyme, in its various glycosylated forms leads to signal misinterpretations, wreaking havoc. However, organisms are endowed with serine protease inhibitors which might restrain this ubiquitous yet deleterious enzyme. Hence, serine proteases-driven pathogenesis and antagonising role of inhibitors is the focal point of this critical review.

Multi-Approach Analysis for the Identification of Proteases within Birch Pollen

Birch pollen allergy is highly prevalent, with up to 100 million reported cases worldwide. Proteases in such allergen sources have been suggested to contribute to primary sensitisation and exacerbation of allergic disorders. Until now the protease content of Betula verrucosa, a birch species endemic to the northern hemisphere has not been studied in detail. Hence, we aim to identify and characterise pollen and bacteria-derived proteases found within birch pollen. The pollen transcriptome was constructed via de novo transcriptome sequencing and analysis of the proteome was achieved via mass spectrometry; a cross-comparison of the two databases was then performed. A total of 42 individual proteases were identified at the proteomic level. Further clustering of proteases into their distinct catalytic classes revealed serine, cysteine, aspartic, threonine, and metallo-proteases. Further to this, protease activity of the pollen was quantified using a fluorescently-labelled casein substrate protease assay, as 0.61 ng/mg of pollen. A large number of bacterial strains were isolated from freshly collected birch pollen and zymographic gels with gelatinase and casein, enabled visualisation of proteolytic activity of the pollen and the collected bacterial strains. We report the successful discovery of pollen and bacteria-derived proteases of Betula verrucosa.

Xerotolerant Cladosporium sphaerospermum Are Predominant on Indoor Surfaces Compared to Other Cladosporium Species

Indoor fungi are a major cause of cosmetic and structural damage of buildings worldwide and prolonged exposure of these fungi poses a health risk. Aspergillus, Penicillium and Cladosporium species are the most predominant fungi in indoor environments. Cladosporium species predominate under ambient conditions. A total of 123 Cladosporium isolates originating from indoor air and indoor surfaces of archives, industrial factories, laboratories, and other buildings from four continents were identified by sequencing the internal transcribed spacer (ITS), and a part of the translation elongation factor 1α gene (TEF) and actin gene (ACT). Species from the Cladosporium sphaerospermum species complex were most predominant representing 44.7% of all isolates, while the Cladosporium cladosporioides and Cladosporium herbarum species complexes represented 33.3% and 22.0%, respectively. The contribution of the C. sphaerospermum species complex was 23.1% and 58.2% in the indoor air and isolates from indoor surfaces, respectively. Isolates from this species complex showed growth at lower water activity (≥ 0.82) when compared to species from the C. cladosporioides and C. herbarum species complexes (≥ 0.85). Together, these data indicate that xerotolerance provide the C. sphaerospermum species complex advantage in colonizing indoor surfaces. As a consequence, C. sphaerospermum are proposed to be the most predominant fungus at these locations under ambient conditions. Findings are discussed in relation to the specificity of allergy test, as the current species of Cladosporium used to develop these tests are not the predominant indoor species.

Alt a 15 is a new cross-reactive minor allergen of Alternaria alternata

Alternaria alternata is one of the most common saprophytes worldwide that is clinically and epidemiologically associated with severe asthma. Therefore, the identification and characterization of all A. alternata allergens are of major clinical importance. This study describes a new cross-reactive A. alternata allergen that was officially named Alt a 15 by the official Allergen Nomenclature Subcommittee. The complete coding region for Alt a 15 was amplified using 5' and 3' rapid amplification of cDNA ends and PCR. The recombinant protein was produced in Escherichia coli as a 65-kDa fusion protein, and the protein sequence exhibits high homology with several important fungal allergens. Immunoblotting analyses revealed that IgE antibodies from A. alternata-sensitized patients (n=59) bound to rAlt a 15 with a prevalence of 10.2%. All patients who presented sIgE to rAlt a 15 were apparently poly-sensitized to A. alternata and C. lunata. The extensive cross-reactivity between A. alternata and C. lunata serine proteases was confirmed using immunoblotting inhibition assays. Overall, Alt a 15 is an important new cross-reactive allergen of A. alternata that explains some allergies to A. alternata without Alt a 1 sensitization and initial diagnostic errors for allergies to Alternaria. This molecule may improve the accuracy of the diagnosis, the understanding, and the management of IgE-mediated fungal diseases.

Antifungal activity and chemical composition of twenty essential oils against significant indoor and outdoor toxigenic and aeroallergenic fungi

Health affecting, loss-inducing or otherwise harmful fungal pathogens (molds) pose a serious challenge in many areas of human activities. On the contrary, frequent use of synthetic fungicides is undesirable in some cases and may be equally problematic. Moreover, the ever more increasing fungal resistance against commercial synthetic fungicides justifies development of rising efforts to seek new effective, while environmentally friendly alternatives. Botanical fungicides based on Essential oils (EOs) undoubtedly provide such an alternative. The study explores the efficacy of 20 EOs against Alternaria alternata, Stachybotrys chartarum, Cladosporium cladosporioides and Aspergillus niger, related to abundance of majority active substances. Minimum inhibitory concentration (MIC100 and MIC50) was evaluated. GC-MS analysis revealed high abundance of highly effective phenolic compounds whose different molecular structures correlates with differences in EOs efficacy. The efficacy of some EOs, observed in our study, can be similar to the levels of some synthetic fungicides used in medicine and agriculture e.g. sometimes problematic azole-based formulations. Thanks to the EOs environmental safety and natural origin, they offer the potential to become an alternative where the use of synthetic fungicides is impossible for various reasons.

Innate affairs of allergens

Activation of receptors of the innate immune system is a critical step in the initiation of immune responses. It has been shown that dominant allergens have properties that could allow them to interact with toll-like and C-type lectin receptors to favour Th2-biased responses and many bind lipids and glycans that could associate with ligands to mimic pathogen-associated microbial patterns. In accord with the proposed allergen-specific innate interactions it has been shown that the immune responses to different allergens and antigens from the same source are not necessarily coordinately regulated.

Characterization of recombinant per a 10 from Periplaneta americana

Cockroach allergen is a major risk factor for IgE-mediated allergic response and asthma in sensitized individuals. Serine proteases have been identified from various sources and characterized as major allergens. The present study was aimed to express and characterize recombinant allergen Per a 10 (rPer a 10) from Periplaneta americana. rPer a 10 was expressed in Escherichia coli and purified in soluble form, yielding 0.75 mg/liter of culture. Homology of the Per a 10 protein sequence exhibited 27 to 38% similarity to the mite serine protease and 41 to 52% similarity to other insect trypsins. The purified rPer a 10 protein resolved at 28 kDa on SDS-PAGE and was recognized by cockroach-hypersensitive patients' sera by immunoblotting and enzyme-linked immunosorbent assay (ELISA). In competitive ELISA, rPer a 10 required 96 ng of purified protein for 50% inhibition of IgE binding, whereas 34 ng of native protein (nPer a 10) was required for the same inhibition. rPer a 10 and nPer a 10 induced basophil histamine release in the range of 47 to 64% and 60 to 85%, respectively, when sensitized with cockroach-hypersensitive patients' sera. In conclusion, Per a 10 was subcloned, and the protein was purified to homogeneity. rPer a 10 showed reduced IgE binding and histamine release and showed no proteolytic activity. These data suggest that rPer a 10 has potential for immunotherapy.

Transaldolases are novel and immunoglobulin E cross-reacting fungal allergens

BACKGROUND

Mould-induced atopic respiratory diseases are a worldwide problem. Characterization of fungal allergens is of major clinical importance.

OBJECTIVE

We identified a novel transaldolase family allergen of Cladosporium and Penicillium species.

METHODS

Fungal allergens were identified by immunoblotting, peptide mass mapping and partial sequencing, cDNA cloning and IgE epitope mapping.

RESULTS

A 36.5 kDa IgE-binding component in a partially purified C. cladosporioides preparation was identified. Mass spectrometric analyses suggest that this novel IgE-reacting allergen is a transaldolase. A corresponding full-length 1246 bp cDNA encoding a polypeptide of 325 residues was isolated. The newly identified transaldolase allergen has been designated as Cla c 14.0101. The cDNA encoding the Pencillium chrysogenum transaldolase was isolated by RT-PCR according to the cDNA sequence encoding a P. chrysogenum Wisconsin 54-1255 hypothetical protein. The purified rCla c 14.0101 protein reacted with IgE antibodies in 10 (38%) of 26 Cladosporium cladosporioides-sensitized asthmatic patients. Nine of the 10 rCla c 14.0101-positive sera have IgE binding against the recombinant Penicillium transaldolase (rPen ch 35.0101). Among the eight fungal transaldolase-positive sera tested, three showed IgE binding against the recombinant human transaldolase. To determine cross-reactivity between the Cladosporium and Penicillium fungi, IgE cross-reactivity was detected between these two fungal transaldolase allergens by inhibition assays. Both the N- and the C-terminal fragments of Cla c 14.0101 were recognized by IgE antibodies. The C-terminal IgE-reacting determinant was narrowed down to a region encompassing Thr257 to Ser278 of Cla c 14.0101. It was mapped onto a loop-like structure of a 3D model constructed for Cla c 14.0101.

CONCLUSION AND CLINICAL RELEVANCE

We identified transaldolase as a novel and IgE cross-reactive allergen family of C. cladosporioides and P. chrysogenum. In addition, an IgE-reacting fragment (Thr257 to Ser278) was pinpointed to a loop-like structure on Cla c 14.0101. Results obtained provide important information in clinical mould allergy.

Role of Allergen Source-Derived Proteases in Sensitization via Airway Epithelial Cells

Protease activity is a characteristic common to many allergens. Allergen source-derived proteases interact with lung epithelial cells, which are now thought to play vital roles in both innate and adaptive immune responses. Allergen source-derived proteases act on airway epithelial cells to induce disruption of the tight junctions between epithelial cells, activation of protease-activated receptor-2, and the production of thymic stromal lymphopoietin. These facilitate allergen delivery across epithelial layers and enhance allergenicity or directly activate the immune system through a nonallergic mechanism. Furthermore, they cleave regulatory cell surface molecules involved in allergic reactions. Thus, allergen source-derived proteases are a potentially critical factor in the development of allergic sensitization and appear to be strongly associated with heightened allergenicity.

Cutaneous yeast microflora in patients with atopic dermatitis

The skin of persons with atopic dermatitis (AD) is very susceptible to cutaneous infection, and some yeast species may also aggravate AD. The total yeast population of an AD patient’s skin and its relation with individual age and body part remains poorly characterized. The aim of this study was to clarify the differences in cutaneous yeast flora by age and body parts of AD patients.

By swabbing affected body parts (hands, legs, face, neck or trunk), 241 samples were collected from patients with AD (132 children and 109 adults), and as controls, 40 samples were taken from healthy individuals (20 children, 20 adults).

In all, 89 (36.9%) of samples were positive; the yeast isolated belonged to three genera: Candida (27.4%), Malassezia (6.6%), and Rhodotorula (2.9%). Cutaneous colonization with yeasts was two-fold higher in the adults than in children (P<0.0001). The distribution of the yeast species was dependent on the body part sampled: Malassezia predominated in the face, neck, and trunk regions (P=0.0047); Candida more frequently colonized hands and legs (P=0.0029).

Our study showed that cutaneous yeast flora and distribution of yeast species depends significantly on the age of the AD patient and the body part affected by atopic dermatitis.

Potential of coculture in vitro models to study inflammatory and sensitizing effects of particles on the lung

Exposure to particulate matter (PM) like nanoparticles (NPs) has increased in the last century due to increased combustion processes, road traffic, etc. In addition, the progress in chemical and cosmetic industry led to many new compounds, e.g. fragrances, which humans are exposed to every day. Many chemicals are known to act as contact and some as respiratory sensitizers, causing allergic reactions. Exposure to small particles of less than 100 nm in diameter is linked with an increased risk of respiratory diseases, such as asthma or rhinitis. To date already more than 1000 customer products contain eNPs without knowing much about the health effects. In comparison to chemicals, the mechanisms by which PM and eNPs can cause sensitization are still not fully understood. Validated and regulatory accepted in vitro models to assess this hazard in its full range are still missing. While a huge number of animal studies contributed to our knowledge about sensitization processes, knowledge on involved cellular mechanisms is still limited. In this review relevant in vitro models to study and elucidate these mechanisms in more detail are presented and their potential to serve as part of a tiered testing strategy is discussed.

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.

Interactions of airway epithelium with protease allergens in the allergic response

Among the apparently innocuous environmental proteins routinely inhaled by human subjects, only a small proportion of these antigens triggers allergy in susceptible individuals. Although the molecular basis of the allergenicity of these airborne proteins remains to be fully characterized, numerous studies suggest that the ability of such proteins to promote allergic responses is at least due to their proteolytic activity. This review will summarize insights into the interactions of protease allergens with the respiratory epithelium. In addition to their capacity to facilitate their antigen presentation through epithelial barrier degradation, protease allergens can directly activate airway mucosal surfaces to recruit inflammatory cells and to initiate the airway remodelling process. A greater understanding of the effects of protease allergens in the airways inflammation as well as on the relevant targets could define novel therapeutic strategies for the treatment allergic asthma.

Elevated atmospheric carbon dioxide concentrations amplify Alternaria alternata sporulation and total antigen production

BACKGROUND

Although the effect of elevated carbon dioxide (CO2) concentration on pollen production has been established in some plant species, impacts on fungal sporulation and antigen production have not been elucidated.

OBJECTIVE

Our purpose was to examine the effects of rising atmospheric CO2 concentrations on the quantity and quality of fungal spores produced on timothy (Phleum pratense) leaves.

METHODS

Timothy plants were grown at four CO2 concentrations (300, 400, 500, and 600 micromol/mol). Leaves were used as growth substrate for Alternaria alternata and Cladosporium phlei. The spore abundance produced by both fungi, as well as the size (microscopy) and antigenic protein content (ELISA) of A. alternata, were quantified.

RESULTS

Leaf carbon-to-nitrogen ratio was greater at 500 and 600 micromol/mol, and leaf biomass was greater at 600 micromol/mol than at the lower CO2 concentrations. Leaf carbon-to-nitrogen ratio was positively correlated with A. alternata spore production per gram of leaf but negatively correlated with antigenic protein content per spore. At 500 and 600 micromol/mol CO2 concentrations, A. alternata produced nearly three times the number of spores and more than twice the total antigenic protein per plant than at lower concentrations. C. phlei spore production was positively correlated with leaf carbon-to-nitrogen ratio, but overall spore production was much lower than in A. alternata, and total per-plant production did not vary among CO2 concentrations.

CONCLUSIONS

Elevated CO2 concentrations often increase plant leaf biomass and carbon-to-nitrogen ratio. Here we demonstrate for the first time that these leaf changes are associated with increased spore production by A. alternata, a ubiquitous allergenic fungus. This response may contribute to the increasing prevalence of allergies and asthma.

IgE sensitization to fungi mirrors fungal phylogenetic systematics

BACKGROUND

Fungal allergy is an elusive disease, and little progress has been made in this field during recent years. Moreover, because of the complexity of the organisms, it is difficult to categorize fungi systematically on the basis of morphologic characterization. However, recent molecular phylogenetics studies have substantially improved fungal categorization. In parallel, new approaches to analyze large IgE antibody datasets enable identification and visualization of IgE sensitization patterns.

OBJECTIVE

To study whether molecular phylogenetic relationships of fungal species, commonly used in allergy diagnosis, also are reflected in IgE sensitization profiles of individuals sensitized to fungi.

METHODS

A dataset was compiled of recorded serum IgE antibody levels to 17 different fungal species from 668 individuals sensitized to at least 1 of the 17 species. By applying a clustering method to this dataset, the fungal species were grouped into a hierarchical organization. Finally, the resulting organization was compared with recently published fungal systematics.

RESULTS

The hierarchical structure of fungi, based on the presence of IgE antibodies in sensitized individuals, very well reflected phylogenetic relationships. Examples include the distinct separation of basal fungi from the subkingdom Dikarya as well as individual cluster formations of fungi belonging to the subphylum Saccharomycotina and order Pleosporales.

CONCLUSION

To our knowledge, this is the first in-depth study that demonstrates a close relationship between molecular fungal systematics and IgE sensitization to fungal species. Because close evolutionary organisms typically have a higher degree of protein similarity, IgE cross-reactivity is likely the main reason for obtained organization.