Der f 35: An MD-2-like house dust mite allergen that cross-reacts with Der f 2 and Pso o 2

Site-specific tyrosine nitration of group 1 allergens of house dust mite Dermatophagoides farinae (der f 1) and Dermatophagoides pteronyssinus (der p 1) in indoor dusts

Nitration can enhance the allergenicity of proteins. The nitration status of house dust mite (HDM) allergens in indoor dusts, however, remains to be elucidated. In the study, site-specific tyrosine nitration degrees of the two important HDM allergens Der f 1 and Der p 1 in indoor dust samples were investigated by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The measured concentrations of native and nitrated allergens in the dusts were in the range of 0.86-29 μg g^-1 for Der f 1 and from below the detection limit to 29 μg g^-1 for Der p 1. Site-specific analysis revealed that all ten tyrosine residues in Der f 1 and Der p 1 were nitrated to different degrees in the investigated samples. The preferred nitration sites were Y₅₆ in Der f 1 and Y₃₇ in Der p 1 with the nitration degrees of 7.6-84% and 17-96% among the detected tyrosine residues, respectively. The measurements reveal high site-specific nitration degrees for tyrosine in Der f 1 and Der p 1 detected in the indoor dust samples. Further investigations are required to find out if the nitration really aggravates the health effects of HDM allergens and if the effects are tyrosine site-dependent.

The HDM allergen orchestra and its cysteine protease maestro: Stimulators of kaleidoscopic innate immune responses

House dust mite (HDM) encloses an explosive cocktail of allergenic proteins sensitizing hundreds of millions of people worldwide. To date, the innate cellular and molecular mechanism(s) orchestrating the HDM-induced allergic inflammation remains partially deciphered. Understanding the kaleidoscope of HDM-induced innate immune responses is hampered by (1) the large complexity of the HDM allergome with very diverse functional bioreactivities, (2) the perpetual presence of microbial compounds (at least LPS, β-glucan, chitin) promoting as well pro-Th2 innate signaling pathways and (3) multiple cross-talks involving structural, neuronal and immune cells. The present review provides an update on the innate immune properties, identified so far, of multiple HDM allergen groups. Experimental evidence highlights the importance of HDM allergens displaying protease or lipid-binding activities on the initiation of the allergic responses. Specifically, group 1 HDM cysteine proteases are considered as the key initiators of the allergic response through their capacities to impair the epithelial barrier integrity, to stimulate the release of pro-Th2 danger-associated molecular patterns (DAMPs) in epithelial cells, to produce super-active forms of IL-33 alarmin and to mature thrombin leading to Toll-like receptor 4 (TLR4) activation. Remarkably, the recently evidenced primary sensing of cysteine protease allergens by nociceptive neurons confirms the critical role of this HDM allergen group in the early events leading to Th2 differentiation.

Chromosome-level assembly of Dermatophagoides farinae genome and transcriptome reveals two novel allergens Der f 37 and Der f 39

Accurate house dust mite (HDM) genome and transcriptome data would promote our understanding of HDM allergens. We sought to assemble chromosome-level genome and precise transcriptome profiling of Dermatophagoides farinae and identify novel allergens. In this study, genetic material extracted from HDM bodies and eggs were sequenced. Short-reads from next generation sequencing (NGS) and long-reads from PacBio/Nanopore sequencing were used to construct the D. farinae nuclear genome, transcriptome, and mitochondrial genome. The candidate homologs were screened through aligning our assembled transcriptome data with amino acid sequences in the WHO/IUIS database. Our results showed that compared with the D. farinae draft genome, bacterial DNA content in the presently developed sequencing reads was dramatically reduced (from 22.9888% to 1.5585%), genome size was corrected (from 53.55 Mb to 58.77 Mb), and the contig N50 was increased (from 8.54 kb to 9365.49 kb). The assembled genome has 10 contigs with minimal microbial contamination, 33 canonical allergens and 2 novel allergens. Eight homologs (≥50% homology) were cloned; 2 bound HDM allergic-sera and were identified as allergens (Der f 37 and Der f 39). In conclusion, a chromosome-level genome, transcriptome and mitochondrial genome of D. farinae was generated to support allergen identification and development of diagnostics and immunotherapeutic vaccines.

Der p 38 Is a Bidirectional Regulator of Eosinophils and Neutrophils in Allergy

The house dust mite is the most common cause of allergic diseases, and TLR4 acts as an overarching receptor for allergic responses. This study aimed to identify novel allergen binding to TLR4 in house dust mites and unveil its unique role in allergic responses. Der p 38 was purified and characterized by liquid chromatography tandem mass spectrometry-based peptide mapping. Biolayer interferometry and structure modeling unveiled TLR4-binding activity and the structure of recombinant Der p 38. The allergenicity of Der p 38 was confirmed by a skin prick test, and basophil activation and dot blot assays. The skin prick test identified 24 out of 45 allergic subjects (53.3%) as Der p 38⁺ subjects. Der p 38-augmented CD203c expression was noted in the basophils of Der p 38⁺ allergic subjects. In animal experiments with wild-type and TLR4 knockout BALB/c mice, Der p 38 administration induced the infiltration of neutrophils as well as eosinophils and exhibited clinical features similar to asthma via TLR4 activation. Persistent Der p 38 administration induced severe neutrophil inflammation. Der p 38 directly suppressed the apoptosis of allergic neutrophils and eosinophils, and enhanced cytokine production in human bronchial epithelial cells, inhibiting neutrophil apoptosis. The mechanisms involved TLR4, LYN, PI3K, AKT, ERK, and NF-κB. These findings may contribute to a deep understanding of Der p 38 as a bridge allergen between eosinophilic and neutrophilic inflammation in the pathogenic mechanisms of allergy.

Myeloid differentiation protein-2 has a protective role in house dust mite-mediated asthmatic characteristics with the proinflammatory regulation of airway epithelial cells and dendritic cells

BACKGROUND

Myeloid differentiation protein-2 (MD-2) is a lipopolysaccharide-binding protein involved in lipopolysaccharide signalling via Toll-like receptor 4 (TLR4). TLR4 plays an essential role in HDM-mediated allergic airway inflammation. Moreover, MD-2 is structurally similar to Der f 2, a major allergen from house dust mite (HDM).

OBJECTIVES

We aimed to clarify the role of MD-2 in the pathogenesis of HDM-mediated allergic airway inflammation.

METHODS

Wild-type (WT), TLR4 knockout and MD-2 knockout mice were subjected to intranasal instillation of HDM extract, and asthmatic features were evaluated. We also evaluated gene sets regulated by MD-2 in HDM-treated airway epithelial cells and examined the function of dendritic cells from lymph nodes and from lungs.

RESULTS

Aggravated allergic airway inflammation with increased airway hyperresponsiveness was observed in MD-2 knockout mice compared with WT and TLR4 knockout mice. Global gene expression analysis revealed an MD-2 regulated proinflammatory response and reconstituted TLR4 signalling in airway epithelial cells. The ability of dendritic cells to evoke an allergic immune response was enhanced in MD-2 knockout mice.

CONCLUSIONS & CLINICAL RELEVANCE

MD-2 plays a protective role in HDM-induced airway allergy with the proinflammatory regulation of airway epithelial cells and dendritic cells. MD-2 may serve as a therapeutic target in the treatment of asthma.

Der f 38 Is a Novel TLR4-Binding Allergen Related to Allergy Pathogenesis from Dermatophagoides farinae

It is difficult to treat allergic diseases including asthma completely because its pathogenesis remains unclear. House dust mite (HDM) is a critical allergen and Toll-like receptor (TLR) 4 is a member of the toll-like receptor family, which plays an important role in allergic diseases. The purpose of this study was to characterize a novel allergen, Der f 38 binding to TLR4, and unveil its role as an inducer of allergy. Der f 38 expression was detected in the body and feces of Dermatophagoides farinae (DF). Electron microscopy revealed that it was located in the granule layer, the epithelium layer, and microvilli of the posterior midgut. The skin prick test showed that 60% of allergic subjects were Der f 38-positive. Der f 38 enhanced surface 203c expression in basophils of Der f 38-positive allergic subjects. By analysis of the model structure of Der p 38, the expected epitope sites are exposed on the exterior side. In animal experiments, Der f 38 triggered an infiltration of inflammatory cells. Intranasal (IN) administration of Der f 38 increased neutrophils in the lung. Intraperitoneal (IP) and IN injections of Der f 38 induced both eosinophils and neutrophils. Increased total IgE level and histopathological features were found in BALB/c mice treated with Der f 38 by IP and IN injections. TLR4 knockout (KO) BALB/c mice exhibited less inflammation and IgE level in the sera compared to wild type (WT) mice. Der f 38 directly binds to TLR4 using biolayer interferometry. Der f 38 suppressed the apoptosis of neutrophils and eosinophils by downregulating proteins in the proapoptotic pathway including caspase 9, caspase 3, and BAX and upregulating proteins in the anti-apoptotic pathway including BCL-2 and MCL-1. These findings might shed light on the pathogenic mechanisms of allergy to HDM.

Characterization of Innate Immune Responses to House Dust Mite Allergens: Pitfalls and Limitations

Whereas house dust mite (HDM) allergy results from a dysregulated Th2-biased adaptive immune response, activation of innate immune signaling pathways is a critical prerequisite for the initiation of HDM sensitizations. Such innate sensing is mainly controlled by the airway epithelium and the skin. The resulting release of epithelial-derived proinflammatory cytokines and innate alarmins such as GM-CSF, IL-25, IL-33 and TSLP mediates the activation of ILC2 cells and cDCs to promote Th2-biased inflammation. Significant progress in the elucidation of HDM innate immune activation has been made in the past decade and highlighted key roles of the LPS/TLR4 axis, chitin-dependent pathways together with HDM protease allergens. However, the precise mechanisms by which HDM allergens are sensed by the innate immune system remain largely unknown. Such investigations are made difficult for several reasons. Among these are (1) the natural association of HDM allergens with immunostimulators from the mite exoskeleton as well as from environmental microorganisms/pollutants or endosymbiotic bacteria; (2) the purification of individual HDM allergens from extracts in sufficient amounts and devoid of any microbial and protein impurities; (3) the production of correctly folded recombinant HDM allergens which could display the same biological activity than their natural counterparts; (4) the accessibility to human epithelial samples with cellular heterogeneities and inter-donor variations; (5) the translation of experimental data from mouse models to humans is almost missing. The goal of the present mini-review is to emphasize some important limitations and pitfalls in the elucidation of innate immunostimulatory properties of HDM allergens.

Temperature stress response: A novel important function of Dermatophagoides farinae allergens

Dermatophagoides farinae, an important pathogen, has multiple allergens. However, their expression under physiological conditions are not understood. Our previous RNA-seq showed that allergens of D. farinae were up-regulated under temperature stress, implying that they may be involved in stress response. Here, we performed a comprehensive study. qRT-PCR detection indicated that 26 of the 34 allergens showed differential expression. Der f1 had the most abundant basic expression quantity. Der f 28.0201 (HSP70) and Der f3 had the same regulation pattern in 9 highly expressed transcripts, which only up-regulated at 41 °C and 43 °C, but Der f 28.0201 showed stronger regulation than Der f 3 (19.88-fold vs 6.02-fold). Whereas Der f 1, 2, 7, 21, 22, 27, and 30 were up-regulated under both heat and cold stress, and Der f 27 showed the strongest regulation ability among them. Der f 27 showed more significant up-regulation than Der f 28.0201 under heat stress (23.59-fold vs 19.88-fold), and Der f27 had more obvious up-regulation under cold than heat stress (30.70-fold vs 23.59-fold). The expression of Der f 27, 28.0201 and 1, and D. farinae survival rates significantly decreased following RNAi, indicating the upregulation of these allergens under temperature stress conferred thermo-tolerance or cold-tolerance to D. farinae. In this study, we described for the first time that these allergens have temperature-stress response functions. This new scientific discovery has important clinical value for revealing the more frequent and serious allergic diseases caused by D. farinae during the change of seasons.

Proteolytic, lipidergic and polysaccharide molecular recognition shape innate responses to house dust mite allergens

House dust mites (HDMs) are sources of an extensive repertoire of allergens responsible for a range of allergic conditions. Technological advances have accelerated the identification of these allergens and characterized their putative roles within HDMs. Understanding their functional bioactivities is illuminating how they interact with the immune system to cause disease and how interrelations between them are essential to maximize allergic responses. Two types of allergen bioactivity, namely proteolysis and peptidolipid/lipid binding, elicit IgE and stimulate bystander responses to unrelated allergens. Much of this influence arises from Toll-like receptor (TLR) 4 or TLR2 signalling and, in the case of protease allergens, the activation of additional pleiotropic effectors with strong disease linkage. Of related interest is the interaction of HDM allergens with common components of the house dust matrix, through either their binding to allergens or their autonomous modulation of immune receptors. Herein, we provide a contemporary view of how proteolysis, lipid-binding activity and interactions with polysaccharides and polysaccharide molecular recognition systems coordinate the principal responses which underlie allergy. The power of the catalytically competent group 1 HDM protease allergen component is demonstrated by a review of disclosures surrounding the efficacy of novel inhibitors produced by structure-based design.

A genomic analysis and transcriptomic atlas of gene expression in Psoroptes ovis reveals feeding- and stage-specific patterns of allergen expression

Background

Psoroptic mange, caused by infestation with the ectoparasitic mite, Psoroptes ovis, is highly contagious, resulting in intense pruritus and represents a major welfare and economic concern for the livestock industry Worldwide. Control relies on injectable endectocides and organophosphate dips, but concerns over residues, environmental contamination, and the development of resistance threaten the sustainability of this approach, highlighting interest in alternative control methods. However, development of vaccines and identification of chemotherapeutic targets is hampered by the lack of P. ovis transcriptomic and genomic resources.

Results

Building on the recent publication of the P. ovis draft genome, here we present a genomic analysis and transcriptomic atlas of gene expression in P. ovis revealing feeding- and stage-specific patterns of gene expression, including novel multigene families and allergens. Network-based clustering revealed 14 gene clusters demonstrating either single- or multi-stage specific gene expression patterns, with 3075 female-specific, 890 male-specific and 112, 217 and 526 transcripts showing larval, protonymph and tritonymph specific-expression, respectively. Detailed analysis of P. ovis allergens revealed stage-specific patterns of allergen gene expression, many of which were also enriched in “fed” mites and tritonymphs, highlighting an important feeding-related allergenicity in this developmental stage. Pair-wise analysis of differential expression between life-cycle stages identified patterns of sex-biased gene expression and also identified novel P. ovis multigene families including known allergens and novel genes with high levels of stage-specific expression.

Conclusions

The genomic and transcriptomic atlas described here represents a unique resource for the acarid-research community, whilst the OrcAE platform makes this freely available, facilitating further community-led curation of the draft P. ovis genome.

Proteomic Analysis Reveals Allergen Variability among Breeds of the Dust Mite Blomia tropicalis

BACKGROUND

The dawn of the "omics" technologies has changed allergy research, increasing the knowledge and identification of new allergens. However, these studies have been almost restricted to Dermatophagoides spp. Although Blomia tropicalis has long been established as a clinically important source of allergens, a thorough proteomic characterization is still lacking for this dust mite.

OBJECTIVE

To increase knowledge of B. tropicalis allergens through proteomic analysis.

METHODS

Eleven in-bred lineages of B. tropicalis were obtained from 11 unique different pregnant females. Their somatic extracts were analyzed and compared with a commercially available extract by liquid chromatography tandem mass spectrometry (LC-MS/MS).

RESULTS

Considerable differences in the protein expression profiles were found among the breeds, and most of them displayed higher expression levels of major allergens than the commercially available extract. Blo t 2 was the most prominent allergenic protein in the analyzed extracts. Six identified allergens and 14 isoforms have not yet been recognized by IUIS. Conversely, 3 previously recognized B. tropicalis allergens were not found.

CONCLUSIONS

The clear impact of inbreeding on allergen content shown by our study leads us to conclude that the quantification and/or identification of allergens from in-bred lines should be routinely considered for mite cultivation in order to select breeds with higher amounts of major allergens. In this sense, LC-MS/MS may be a useful method to achieve this quality control for research and commercial purposes.

A robust method for the estimation and visualization of IgE cross-reactivity likelihood between allergens belonging to the same protein family

Among the vast number of identified protein families, allergens emanate from relatively few families which translates to only a small fraction of identified protein families. In allergy diagnostics and immunotherapy, interactions between immunoglobulin E and allergens are crucial because the formation of an allergen-antibody complex is necessary for triggering an allergic reaction. In allergic diseases, there is a phenomenon known as cross-reactivity. Cross-reactivity describes a situation where an individual has produced antibodies against a particular allergenic protein, but said antibodies fail to discriminate between the original sensitizer and other similar proteins that usually belong to the same family. To expound the concept of cross-reactivity, this study examines ten protein families that include allergens selected specifically for the analysis of cross-reactivity. The selected allergen families had at least 13 representative proteins, overall folds that differ significantly between families, and include relevant allergens with various potencies. The selected allergens were analyzed using information on sequence similarities and identities between members of the families as well as reports on clinically relevant cross-reactivities. Based on our analysis, we propose to introduce a new A-RISC index (Allergens’–Relative Identity, Similarity and Cross-reactivity) which describes homology between two allergens belonging to the same protein family and is used to predict the likelihood of cross-reactivity between them. Information on sequence similarities and identities, as well as on the values of the proposed A-RISC index is used to introduce four categories describing a risk of a cross-reactive reaction, namely: high, medium-high, medium-low and low. The proposed approach can facilitate analysis in component-resolved allergy diagnostics, generation of avoidance guidelines for allergic individuals, and help with the design of immunotherapy.

A combined transcriptome and proteome analysis extends the allergome of house dust mite Dermatophagoides species

Background

House dust mites (HDMs) such as Dermatophagoides farinae and D. pteronyssinus represent major causes of perennial allergy. HDM proteomes are currently poorly characterized, with information mostly restricted to allergens. As of today, 33 distinct allergen groups have been identified for these 2 mite species, with groups 1 and 2 established as major allergens. Given the multiplicity of IgE-reactive mite proteins, potential additional allergens have likely been overlooked.

Objective

To perform a comprehensive characterization of the transcriptomes, proteomes and allergomes of D. farinae and D. pteronyssinus in order to identify novel allergens.

Methods

Transcriptomes were analyzed by RNA sequencing and de novo assembly. Comprehensive mass spectrometry-based analyses proteomes were combined with two-dimensional IgE reactivity profiling.

Results

Transcripts from D. farinae and D. pteronyssinus were assembled, translated into protein sequences and used to populate derived sequence databases in order to inform immunoproteomic analyses. A total of 527 and 157 proteins were identified by bottom-up MS analyses in aqueous extracts from purified HDM bodies and fecal pellets, respectively. Based on high sequence similarities (>71% identity), we also identified 2 partial and 11 complete putative sequences of currently undisclosed D. pteronyssinus counterparts of D. farinae registered allergens. Immunoprofiling on 2D-gels revealed the presence of unknown 23 kDa IgE reactive proteins in both species. Following expression of non-glycosylated recombinant forms of these molecules, we confirm that these new allergens react with serum IgEs from 42% (8/19) of HDM-allergic individuals.

Conclusions

Using combined transcriptome and immunoproteome approaches, we provide a comprehensive characterization of D. farinae and D. pteronyssinus allergomes. We expanded the known allergen repertoire for D. pteronyssinus and identified two novel HDM allergens, now officially referred by the International Union of Immunological Societies (IUIS) Nomenclature Subcommittee as Der f 36 and Der p 36.