The crystal structure of a major dust mite allergen Der p 2, and its biological implications

Convergent evolution of innate immune-modulating effectors in invasive fungal pathogens

Invasive fungal infections pose a major threat to human health. Bacterial and protozoan pathogens secrete protein effectors that overcome innate immune barriers to promote microbial colonization, yet few such molecules have been identified in human fungal pathogens. Recent studies have begun to reveal these long-sought effectors and have illuminated how they subvert key cellular pathways, including apoptosis, myeloid cell polarization, Toll-like receptor signaling, and phagosome action. Thus, despite lacking the specialized secretion systems of bacteria and parasites, it is increasingly clear that fungi independently evolved effectors targeting pathways often subverted by other classes of pathogens. These findings demonstrate the remarkable power of convergent evolution to enable diverse microbes to infect humans while also setting the stage for detailed dissection of fungal disease mechanisms.

House Dust Mite Extract Forms a Der p 2 Corona on Multi-Walled Carbon Nanotubes: Implications for Allergic Airway Disease

Multi-walled carbons nanotubes (MWCNTs) are used in materials for the construction, automotive, and aerospace industries. Workers and consumers are exposed to these materials via inhalation. Existing recommended exposure limits are based on MWCNT exposures that do not take into account more realistic co-exposures. Our goal was to understand how a common allergen, house dust mites, interacts with pristine MWCNTs and lung fluid proteins. We used gel electrophoresis, western blotting, and proteomics to characterize the composition of the allergen corona formed from house dust mite extract on the surface of MWCNTs. We found that the corona is dominated by der p 2, a protein associated with human allergic responses to house dust mites. Der p 2 remains adsorbed on the surface of the MWCNTs following subsequent exposures to lung fluid proteins. The high concentration of der p 2, localized on surface of MWCNTs, has important implications for house dust mite-induced allergies and asthma. This research provides a detailed characterization of the complex house dust mite-lung fluid protein coronas for future cellular and in vivo studies. These studies will help to address the molecular and biochemical mechanisms underlying the exacerbation of allergic lung disease by nanomaterials.

Toll-like receptor 4 and Syk kinase shape dendritic cell-induced immune activation to major house dust mite allergens

Background

House dust mite (HDM) is a major cause of respiratory allergic diseases. Dendritic cells (DCs) play a central role in orchestrating adaptive allergic immune responses. However, it remains unclear how DCs become activated by HDM. Biochemical functions of the major HDM allergens Der p 1 (cysteine protease) and Der p 2 (MD2-mimick) have been implicated to contribute to DC activation.

Methods

We investigated the immune activating potential of HDM extract and its major allergens Der p 1 and Der p 2 using monocyte-derived DCs (moDCs). Maturation and activation markers were monitored by flow cytometry and cytokine production by ELISA. Allergen depletion and proteinase K digestion were used to investigate the involvement of proteins, and in particular of the major allergens. Inhibitors of spleen tyrosine kinase (Syk), Toll-like receptor 4 (TLR4) and of C-type lectin receptors (CLRs) were used to identify the involved receptors. The contribution of endotoxins in moDC activation was assessed by their removal from HDM extract.

Results

HDM extract induced DC maturation and cytokine responses in contrast to the natural purified major allergens Der p 1 and Der p 2. Proteinase K digestion and removal of Der p 1 or Der p 2 did not alter the immune stimulatory capacity of HDM extract. Antibodies against the CLRs Dectin-1, Dectin-2, and DC-SIGN did not affect cytokine responses. In contrast, Syk inhibition partially reduced IL-6, IL-12 and completely blocked IL-10. Blocking TLR4 signaling reduced the HDM-induced IL-10 and IL-12p70 induction, but not IL-6, while endotoxin removal potently abolished the induced cytokine response.

Conclusion

Our data strongly suggest that HDM-induced DC activation is neither dependent on Der p 1 nor Der p 2, but depend on Syk and TLR4 activation, which might suggest a crosstalk between Syk and TLR4 pathways. Our data highlight that endotoxins play a potent role in immune responses targeting HDM.

GlycoCAP: A Cell-Free, Bacterial Glycosylation Platform for Building Clickable Azido-Sialoglycoproteins

Glycan-binding receptors known as lectins represent a class of potential therapeutic targets. Yet, the therapeutic potential of targeting lectins remains largely untapped due in part to limitations in tools for building glycan-based drugs. One group of desirable structures is proteins with noncanonical glycans. Cell-free protein synthesis systems have matured as a promising approach for making glycoproteins that may overcome current limitations and enable new glycoprotein medicines. Yet, this approach has not been applied to the construction of proteins with noncanonical glycans. To address this limitation, we develop a cell-free glycoprotein synthesis platform for building noncanonical glycans and, specifically, clickable azido-sialoglycoproteins (called GlycoCAP). The GlycoCAP platform uses an Escherichia coli-based cell-free protein synthesis system for the site-specific installation of noncanonical glycans onto proteins with a high degree of homogeneity and efficiency. As a model, we construct four noncanonical glycans onto a dust mite allergen (Der p 2): α2,3 C5-azido-sialyllactose, α2,3 C9-azido-sialyllactose, α2,6 C5-azido-sialyllactose, and α2,6 C9-azido-sialyllactose. Through a series of optimizations, we achieve more than 60% sialylation efficiency with a noncanonical azido-sialic acid. We then show that the azide click handle can be conjugated with a model fluorophore using both strain-promoted and copper-catalyzed click chemistry. We anticipate that GlycoCAP will facilitate the development and discovery of glycan-based drugs by granting access to a wider variety of possible noncanonical glycan structures and also provide an approach for functionalizing glycoproteins by click chemistry conjugation.

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.

The Niemann-Pick type diseases – A synopsis of inborn errors in sphingolipid and cholesterol metabolism

Disturbances of lipid homeostasis in cells provoke human diseases. The elucidation of the underlying mechanisms and the development of efficient therapies represent formidable challenges for biomedical research. Exemplary cases are two rare, autosomal recessive, and ultimately fatal lysosomal diseases historically named "Niemann-Pick" honoring the physicians, whose pioneering observations led to their discovery. Acid sphingomyelinase deficiency (ASMD) and Niemann-Pick type C disease (NPCD) are caused by specific variants of the sphingomyelin phosphodiesterase 1 (SMPD1) and NPC intracellular cholesterol transporter 1 (NPC1) or NPC intracellular cholesterol transporter 2 (NPC2) genes that perturb homeostasis of two key membrane components, sphingomyelin and cholesterol, respectively. Patients with severe forms of these diseases present visceral and neurologic symptoms and succumb to premature death. This synopsis traces the tortuous discovery of the Niemann-Pick diseases, highlights important advances with respect to genetic culprits and cellular mechanisms, and exposes efforts to improve diagnosis and to explore new therapeutic approaches.

EAACI Molecular Allergology User's Guide 2.0

Since the discovery of immunoglobulin E (IgE) as a mediator of allergic diseases in 1967, our knowledge about the immunological mechanisms of IgE-mediated allergies has remarkably increased. In addition to understanding the immune response and clinical symptoms, allergy diagnosis and management depend strongly on the precise identification of the elicitors of the IgE-mediated allergic reaction. In the past four decades, innovations in bioscience and technology have facilitated the identification and production of well-defined, highly pure molecules for component-resolved diagnosis (CRD), allowing a personalized diagnosis and management of the allergic disease for individual patients. The first edition of the "EAACI Molecular Allergology User's Guide" (MAUG) in 2016 rapidly became a key reference for clinicians, scientists, and interested readers with a background in allergology, immunology, biology, and medicine. Nevertheless, the field of molecular allergology is moving fast, and after 6 years, a new EAACI Taskforce was established to provide an updated document. The Molecular Allergology User's Guide 2.0 summarizes state-of-the-art information on allergen molecules, their clinical relevance, and their application in diagnostic algorithms for clinical practice. It is designed for both, clinicians and scientists, guiding health care professionals through the overwhelming list of different allergen molecules available for testing. Further, it provides diagnostic algorithms on the clinical relevance of allergenic molecules and gives an overview of their biology, the basic mechanisms of test formats, and the application of tests to measure allergen exposure.

Human Monoclonal IgE Antibodies-a Major Milestone in Allergy

PURPOSE OF REVIEW

Bound to its high affinity receptor on mast cells and basophils, the IgE antibody molecule plays an integral role in the allergic reaction. Through interactions with the allergen, it provides the sensitivity and specificity parameters for cell activation and mediator release that produce allergic symptoms. Advancements in human hybridoma technologies allow for the generation and molecular definition of naturally occurring allergen-specific human IgE monoclonal antibodies.

RECENT FINDINGS

A high-resolution structure of dust mite allergen Der p 2 in complex with Fab of the human IgE mAb 2F10 was recently determined using X-ray crystallography. The structure reveals the fine molecular details of IgE 2F10 binding its 750 Å2 conformational epitope on Der p 2. This review provides an overview of this major milestone in allergy, the first atomic resolution structure of an authentic human IgE epitope. The molecular insights that IgE epitopes provide will allow for structure-based design approaches to the development of novel diagnostics, antibody therapeutics, and immunotherapies.

Differences in mouse strains determine the outcome of Der p 2 allergy induction protocols

In vivo animal models can provide worthy information on various aspects of asthma mechanism and pathogenesis. The genetic predisposition and phenotype of mice may affect the immune response itself. Here we compare the early immune response to Der p 2 or HDM allergen extract upon injection and inhalation in BALB/c and C57BL/6 mice. Female C57BL/6 and BALB/c mice were immunized with Der p 2 allergen subcutaneously followed by inhalation of Der p 2 or HDM extract. After challenge, the mice were euthanized; blood, bronchoalveolar lavage (BAL), spleens and lungs were collected. Cells from BAL were identified by May-Grünwald Giemsa staining and lung leukocyte populations were analyzed by flow cytometry. Serum antibody levels of Der p 2 specific IgE, IgG, IgG1 and IgG2a were assessed by ELISA, and cytokine secretion (IL-4, IFN-γ and IL-10) was evaluated upon stimulation with Der p 2 or HDM extract. The Th2 immune response was confirmed by elevated allergen-specific immunoglobulin E (IgE) and the allergic reaction was evidenced by infiltration of eosinophils and/or neutrophils into BAL. We found that BALB/c mice were inefficient in integrating local with systemic immune response, evidenced by almost no IgG or IgE production upon one subcutaneous injection and subsequent inhalation of Der p 2 allergen; also, the bronchoalveolar lavage infiltrate in these mice consisted of neutrophil infiltration, unlike C57BL/6 mice in which eosinophilic infiltrate predominated. The differences between BALB/c and C57BL/6 mice strains could be exploited for generating different types of responses to the Der p 2 allergen.

Determination of immunogenic epitopes in major house dust mite allergen, Der p 2, via nanoallergens

BACKGROUND

Despite the high prevalence of allergic asthma, currently, avoidance of the responsible allergens, which is nearly impossible for allergens such as house dust mite (HDM), remains among the most effective treatment. Consequently, determination of the immunogenic epitopes of allergens will aid in developing a better understanding of the condition for diagnostic and therapeutic purposes. Current methods of epitope identification, however, only evaluate immunoglobulin E-epitope binding interactions, which is not directly related to epitope immunogenicity.

OBJECTIVE

To determine and rank the immunogenicity of the epitopes of major HDM allergen, Der p 2.

METHODS

We performed degranulation assays with RBL-SX38 cells primed using patient plasma and challenged with nanoallergens which multivalently displayed epitopes to study the relative immunogenicity of various epitopes of Der p 2. Nanoallergens were used to evaluate epitopes individually or in combination.

RESULTS

When evaluated using 3 patient samples, 3 epitopes in 2 distal regions of Der p 2 were identified as highly immunogenic when presented in combination, whereas no individual epitope triggered relevant degranulation. One of the epitopes (69-DPNACHYMKCPLVKGQQY-86) was identified to be cooperatively immunogenic when combined with other epitopes.

CONCLUSION

Our study highlights the importance of conformational epitopes in HDM-related allergies. This study also provides further evidence of the versatility of nanoallergens and their value for functional characterization of allergy epitopes, by ranking the Der p 2 epitopes according to immunogenicity. We believe that nanoallergens, by aiding in identification and understanding of immunogenic epitopes, will provide a better understanding of the manifestation of the allergic condition and potentially aid in developing new treatments.

Storage Mite Precision Allergy Molecular Diagnosis in the Moderate-to-Severe T2-High Asthma Phenotype

Storage mites (SM) may induce allergic respiratory symptoms in sensitized individuals, in both rural and urban settings. The relationship among specific IgE reactions to determined groups of SM allergens in the coincident asthma pheno-endotypes has not yet been investigated. We aimed to study a Precision Allergy Molecular Diagnosis (PAMD@) model to depict the SM molecular profile in individuals presenting with Type-2 inflammation, in two different (moderate and severe) asthma phenotypes. A customized PAMD@ panel, including SM allergens and their concurrent protein allergenic characterization was investigated. Mite group 2 allergens were most frequently recognized, including Lep d 2 (83.45%), followed by Gly d 2 (69.17%) and Tyr p 2 (47,37%), in 133/164 asthmatic subjects. Blo t 5 and Blo t 21 exhibited significant higher titres in both asthma groups. Although relevant mite group 2 allergens cross-reactivity is suggested, individualized sensitization patterns were relevantly identified. The present PAMD@ panel confirmed the dominance of mite group 2 allergens in moderate-to-severe T2 asthmatics. A broadly heterogeneous molecular repertoire of SM allergens was found in all subjects, regardless of their asthma severity. Blomia tropicalis deserves special attention in certain territories, as diagnostic and/or therapeutic approaches merely based on Pyroglyphidae mites may be insufficient.

Systematic Characterization of the Group 2 House Dust Mite Allergen in Dermatophagoides microceras

Background

Allergic asthma, a chronic airway inflammatory disease, is a critical public health problem. Indoor house dust mites (HDMs) could cause allergic asthma. The prevalence of sensitization to Dermatophagoides microceras (Der m) was approximately 80% and is related to the immunoglobulin E crossing-reactivity of mites belonging to the same genus, Dermatophagoides pteronyssinus (Der p) and Dermatophagoides farina (Der f). However, studies on Der m are scant.

Methods

We used integrated OMICs approaches to identify and characterize the group 2 mite allergen-like protein in Der m (Der m 2). We established a Der m 2-induced allergic asthma mouse model and treated the mice with a fungal immunomodulatory protein (FIP-fve) isolated from Flammulina veluptipes to evaluate the allergenicity of Der m 2 and the immunomodulatory effects of FIP-fve.

Results

By performing de novo draft genome assembly and comparative genome analysis, we identified the putative 144-amino acid Der m 2 in silico and further confirmed its existence through liquid chromatography–tandem mass spectrometry. Der m 2 is a lipopolysaccharides (LPS)-binding protein. Thus, we examined the LPS-binding activity of recombinant Der m 2 by performing molecular docking analysis, co-immunoprecipitation (Co-IP), and a pull-down assay. Der m 2 elicited the production of pro-inflammatory cytokines, interleukin (IL)-6, and IL-8 in BEAS-2B cells, a human bronchial epithelial cell line, and induced airway hyperresponsiveness in mice. Furthermore, in mice sensitized with Der m 2, the administration of FIP-fve in either the earlier stage or the late stage, FIP-fve alleviated allergic asthma by moderating airway inflammation and remodeling.

Conclusions

Der m 2 induced inflammatory responses in cell and mouse models. FIP-fve alleviated inflammation in Der m 2-induced asthma in mice by exerting an immunomodulatory effect.

Allergens and their associated small molecule ligands-their dual role in sensitization

Many allergens feature hydrophobic cavities that allow the binding of primarily hydrophobic small‐molecule ligands. Ligand‐binding specificities can be strict or promiscuous. Serum albumins from mammals and birds can assume multiple conformations that facilitate the binding of a broad spectrum of compounds. Pollen and plant food allergens of the family 10 of pathogenesis‐related proteins bind a variety of small molecules such as glycosylated flavonoid derivatives, flavonoids, cytokinins, and steroids in vitro. However, their natural ligand binding was reported to be highly specific. Insect and mammalian lipocalins transport odorants, pheromones, catecholamines, and fatty acids with a similar level of specificity, while the food allergen β‐lactoglobulin from cow's milk is notably more promiscuous. Non‐specific lipid transfer proteins from pollen and plant foods bind a wide variety of lipids, from phospholipids to fatty acids, as well as sterols and prostaglandin B2, aided by the high plasticity and flexibility displayed by their lipid‐binding cavities. Ligands increase the stability of allergens to thermal and/or proteolytic degradation. They can also act as immunomodulatory agents that favor a Th2 polarization. In summary, ligand‐binding allergens expose the immune system to a variety of biologically active compounds whose impact on the sensitization process has not been well studied thus far.

Lessons in Innate and Allergic Immunity From Dust Mite Feces and Tick Bites

Allergic diseases represent a major cause of morbidity in modern industrialized and developing countries. The origins and development of allergic immune responses have proven difficult to unravel and remain an important scientific objective. House dust mites (HDM) and ticks represent two important causes of allergic disease. Investigations into HDM fecal particles and tick bites have revealed insights which have and will continue to shape our understanding of allergic immunity. In the present review, focus is given to the role of innate immunity in shaping the respective responses to HDM and ticks. The HDM fecal particle represents a rich milieu of molecules that can be recognized by pathogen-recognition receptors of the innate immune system. Factors in tick saliva and/or tissue damage resultant from tick feeding are thought to activate innate immune signaling that promotes allergic pathways. Recent evidence indicates that innate sensing involves not only the direct recognition of allergenic agents/organisms, but also indirect sensing of epithelial barrier disruption. Although fecal particles from HDM and bites from ticks represent two distinct causes of sensitization, both involve a complex array of molecules that contribute to an innate response. Identification of specific molecules will inform our understanding of the mechanisms that contribute to allergic immunity, however the key may lie in the combination of molecules delivered to specific sites in the body.

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.

Removal and Replacement of Endogenous Ligands from Lipid-Bound Proteins and Allergens

Many major allergens bind to hydrophobic lipid-like molecules, including Mus m 1, Bet v 1, Der p 2, and Fel d 1. These ligands are strongly retained and have the potential to influence the sensitization process either through directly stimulating the immune system or altering the biophysical properties of the allergenic protein. In order to control for these variables, techniques are required for the removal of endogenously bound ligands and, if necessary, replacement with lipids of known composition. The cockroach allergen Bla g 1 encloses a large hydrophobic cavity which binds a heterogeneous mixture of endogenous lipids when purified using traditional techniques. Here, we describe a method through which these lipids are removed using reverse-phase HPLC followed by thermal annealing to yield Bla g 1 in either its Apo-form or reloaded with a user-defined mixture of fatty acid or phospholipid cargoes. Coupling this protocol with biochemical assays reveal that fatty acid cargoes significantly alter the thermostability and proteolytic resistance of Bla g 1, with downstream implications for the rate of T-cell epitope generation and allergenicity. These results highlight the importance of lipid removal/reloading protocols such as the one described herein when studying allergens from both recombinant and natural sources. The protocol is generalizable to other allergen families including lipocalins (Mus m 1), PR-10 (Bet v 1), MD-2 (Der p 2) and Uteroglobin (Fel d 1), providing a valuable tool to study the role of lipids in the allergic response.

Design, production and immunomodulatory potency of a novel allergen bioparticle

Allergen immunotherapy (AIT) is the only disease-modifying treatment with evidence for sustained efficacy. However, it is poorly developed compared to symptomatic drugs. The main reasons come from treatment duration implying monthly injections during 3 to 5 years or daily sublingual use, and the risk of allergic side-effects. To become a more attractive alternative to lifelong symptomatic drug use, improvements to AIT are needed. Among the most promising new immunotherapy strategies is the use of bioparticles for the presentation of target antigen to the immune system as they can elicit strong T cell and B cell immune responses. Virus-like particles (VLPs) are a specific class of bioparticles in which the structural and immunogenic constituents are from viral origin. However, VLPs are ill-suited for use in AIT as their antigenicity is linked to structure. Recently, synthetic biology has been used to produce artificial modular bioparticles, in which supramolecular assemblies are made of elements from heterogeneous biological sources promoting the design and use of in vivo-assembling enveloped bioparticles for viral and non-viral antigens presentation. We have used a coiled-coil hybrid assembly for the design of an enveloped bioparticle (eBP) that present trimers of the Der p 2 allergen at its surface, This bioparticle was produced as recombinant and in vivo assembled eBPs in plant. This allergen biotherapeutic was used to demonstrate i) the capacity of plants to produce synthetic supramolecular allergen bioparticles, and ii) the immunomodulatory potential of naturally-assembled allergen bioparticles. Our results show that allergens exposed on eBPs induced a very strong IgG response consisting predominantly of IgG2a in favor of the TH1 response. Finally, our results demonstrate that rDer p 2 present on the surface of BPs show a very limited potential to stimulate the basophil degranulation of patient allergic to this allergen which is predictive of a high safety potential.

Mapping Human Monoclonal IgE Epitopes on the Major Dust Mite Allergen Der p 2

IgE Abs drive the symptoms of allergic disease upon cross-linking allergens on mast cells or basophils. If the IgE binding sites on the allergens could be identified, it may be useful for creating new forms of immunotherapy. However, direct knowledge of the human IgE (hIgE) epitopes is limited because of the very low frequency of IgE-producing B cells in blood. A new hybridoma technology using human B cells from house dust mite-allergic patients was used to identify four Der p 2-specific hIgE mAbs. Their relative binding sites were assessed and compared by immunoassays with three previously studied murine IgG mAbs. Immunoassays showed that the recognition of Der p 2 by the first three hIgE was inhibited by a single murine IgG, but the fourth hIgE recognized a different epitope from all the other mAbs. The functional ability of the hIgE that bind different epitopes to cross-link Der p 2 was demonstrated in a mouse model of passive systemic anaphylaxis. Nuclear magnetic resonance analyses of Der p 2 in complex with IgG and IgE Abs were used to identify specific residues in the epitopes. To our knowledge, the combination of immunoassays to distinguish overlapping epitopes and nuclear magnetic resonance analyses to identify specific residues involved in Ab binding provided the first epitope mapping of hIgE mAbs to an allergen. The technologies developed in this study will be useful in high-resolution mapping of human epitopes on other Ags and the design of improved therapeutics.

Identification the Cross-Reactive or Species-Specific Allergens of Tyrophagus putrescentiae and Development Molecular Diagnostic Kits for Allergic Diseases

Mite allergens are considerable factors in the genesis of allergic diseases. The storage mite Tyrophagus putrescentiae (Tp) appears in contaminated foods and household surroundings. The current diagnostic tools for Tp allergy are mostly based on crude extracts and still contain shortcomings. This study aimed to investigate the immunoglobulin E (IgE)- responsiveness profiles of Tp-allergic patients and develop a molecular diagnostic method using recombinant allergens. Allergenic components were characterized as cross-reacting or species-specific allergens, in which the effective combinations of recombinant allergens were developed and analyzed in terms of the prediction accuracy for clinical diagnosis. Seven recombinant allergens were cloned and generated to detect the IgE responsiveness of the Tp allergy. A survey on the prevalence of mite allergy showed there were higher sensitizations with IgE responsiveness to house dust mites (HDM) (78.9-80.9%) than to storage mites Tp (35.6%). Prevalence of sensitization to Tp was higher in elderly subjects. The principal IgE-binding components of Tp were Tyr p 1, Tyr p 2 and Tyr p 3. Prediction accuracy for Tp allergy by IgE-responsiveness combination D (Tyr p 1, Tyr p 2 & Tyr p 3) was with high precision (100%). Avoiding the cross-reactivity of Dermatophagoides pteronyssinus, the prediction accuracy of IgE-responsiveness combination H+ (Tyr p 1, Tyr p 2, Tyr p 3, Tyr p 7, Tyr p 8, Tyr p 10 & Tyr p 20) was suitable for Tp-specific diagnosis. Panels of Tp allergens were generated and developed a diagnostic kit able beneficial to identify IgE-mediated Tp hypersensitivity.

Hydrophobic ligands influence the structure, stability, and processing of the major cockroach allergen Bla g 1

The cockroach allergen Bla g 1 forms a novel fold consisting of 12 amphipathic alpha-helices enclosing an exceptionally large hydrophobic cavity which was previously demonstrated to bind a variety of lipids. Since lipid-dependent immunoactivity is observed in numerous allergens, understanding the structural basis of this interaction could yield insights into the molecular determinants of allergenicity. Here, we report atomic modelling of Bla g 1 bound to both fatty-acid and phospholipids ligands, with 8 acyl chains suggested to represent full stoichiometric binding. This unusually high occupancy was verified experimentally, though both modelling and circular dichroism indicate that the general alpha-helical structure is maintained regardless of cargo loading. Fatty-acid cargoes significantly enhanced thermostability while inhibiting cleavage by cathepsin S, an endosomal protease essential for antigen processing and presentation; the latter of which was found to correlate to a decreased production of known T-cell epitopes. Both effects were strongly dependent on acyl chain length, with 18-20 carbons providing the maximal increase in melting temperature (~20 °C) while completely abolishing proteolysis. Diacyl chain cargoes provided similar enhancements to thermostability, but yielded reduced levels of proteolytic resistance. This study describes how the biophysical properties of Bla g 1 ligand binding and digestion may relate to antigen processing, with potential downstream implications for immunogenicity.

A Human IgE Antibody Binding Site on Der p 2 for the Design of a Recombinant Allergen for Immunotherapy

Der p 2 is one of the most important allergens from the house dust mite Dermatophagoides pteronyssinus Identification of human IgE Ab binding epitopes can be used for rational design of allergens with reduced IgE reactivity for therapy. Antigenic analysis of Der p 2 was performed by site-directed mutagenesis based on the x-ray crystal structure of the allergen in complex with a Fab from the murine IgG mAb 7A1 that binds an epitope overlapping with human IgE binding sites. Conformational changes upon Ab binding were confirmed by nuclear magnetic resonance using a 7A1-single-chain variable fragment. In addition, a human IgE Ab construct that interferes with mAb 7A1 binding was isolated from a combinatorial phage-display library constructed from a mite-allergic patient and expressed as two recombinant forms (single-chain Fab in Pichia pastoris and Fab in Escherichia coli). These two IgE Ab constructs and the mAb 7A1 failed to recognize two Der p 2 epitope double mutants designed to abolish the allergen-Ab interaction while preserving the fold necessary to bind Abs at other sites of the allergen surface. A 10-100-fold reduction in binding of IgE from allergic subjects to the mutants additionally showed that the residues mutated were involved in IgE Ab binding. In summary, mutagenesis of a Der p 2 epitope defined by x-ray crystallography revealed an IgE Ab binding site that will be considered for the design of hypoallergens for immunotherapy.

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.

Blo t 2: Group 2 allergen from the dust mite Blomia tropicalis

Blomia tropicalis has been recognized as a cause of allergic diseases in the tropical and subtropical regions. Here we report the immuno-characterization of its group 2 allergen, Blo t 2. Allergen Blo t 2 was amplified from the cDNA of B. tropicalis using degenerate primers, expressed in Escherichia coli as a recombinant protein and purified to homogeneity. The mature protein of Blo t 2 was 126 amino acids long with 52% sequence identity to Der p 2 and apparent molecular mass of 15 kDa. Circular dichroism spectroscopy showed that Blo t 2 is mainly a beta-sheeted protein. We confirmed the presence of three disulfide bonds in recombinant (r) Blo t 2 protein using electrospray mass spectrometry. Thirty-four percent of dust-mite allergic individuals from the Singapore showed specific IgE binding to rBlo t 2 as tested using immuno dot-blots. IgE-cross reactivity assays showed that Blo t 2 had between 20-50% of unique IgE-epitopes compared to Der p 2. IgE binding of native and recombinant forms of Blo t 2 were highly concordant (r2 = 0.77, p < 0.0001) to rBlo t 2. Dose-dependent in vitro histamine was observed when rBlo t 2 was incubated with whole blood of Blo t 2 sensitized individuals, demonstrating that it is a functional allergen. Nine naturally occurring isoforms of Blo t 2 were identified in this study, each having between 1-3 amino acid variations compared to the reference clone. Blo t 2 is a clinically relevant allergen of B. tropicalis as it has unique IgE epitopes compared to major group 2 allergens from Dermatophagoides spp.

The characteristics and biological significance of NPC2: Mutation and disease

Niemann-Pick C disease (NPC) is a rare autosomal recessive disorder characterized by severe neurodegeneration of central nervous system. Linkage studies in multiplex NPC families and genetic complementation research revealed two disease genes, NPC1 and NPC2, both of which are important transporters for cholesterol trafficking. NPC2 executes cholesterol-transport function through protein-protein interaction with NPC1 as well as through protein-membrane interaction directly with membrane of late endosome and lysosome. In addition, NPC2 may play many other roles as indicated by its widely expressing pattern in different cells and presenting in numerous secretory fluids, although it biological significance is less studied today. About 50 clinical cases have been reported documenting over twenty different mutations of NPC2 in NPC patients so far. In this review, we will mainly summarize the molecular characteristics and biological significance of NPC2, highlighting its vital roles in NPC disease.

An Engineered Hybrid Protein from Dermatophagoides pteronyssinus Allergens Shows Hypoallergenicity

The house dust mite (HDM) Dermatophagoides pteronyssinus is an important risk factor for asthma and rhinitis. Allergen specific immunotherapy that is based on recombinant proteins has been proposed for the safer and more efficient treatment of allergic diseases. The aim of this study was to design and obtain a hybrid protein (DPx4) containing antigenic regions of allergens Der p 1, Der p 2, Der p 7, and Der p 10 from this mite. DPx4 was produced in Escherichia coli and its folding was determined by circular dichroism. Non-denaturing dot-blot, ELISA, basophil activation test, dot blot with monoclonal antibodies, ELISA inhibition, and cysteine protease activity assays were performed. Mice that were immunized with DPx4 were also analyzed. We found that DPx4 had no cysteine protease activity and it showed significantly lower IgE reactivity than Der p 1, Der p 2, and D. pteronyssinus extract. DPx4 induced lower basophil activation than Der p 2 and the allergen extract. Immunized mice produced IgG antibodies that inhibited the binding of allergic patient’s IgE to the allergen extract and induced comparatively higher levels of IL-10 than the extract in peripheral blood mononuclear cells (PBMC) culture. These results suggest that DPx4 has immunological properties that are useful for the development of a mite allergy vaccine.

The major allergen Der p 2 is a cholesterol binding protein

Der p 2 is a major dust mite allergen and >80% of mite allergic individuals have specific IgE to this allergen. Although it is well characterized in terms of allergenicity, there is still some ambiguity in terms of its biological function. Three-dimensional structural analysis of Der p 2 and its close homologues indicate the presence of a hydrophobic cavity which can potentially bind to lipid molecules. In this study, we aimed to identify the potential ligand of Der p 2. Using a liposome pulldown assay, we show that recombinant Der p 2 binds to liposomes prepared with exogenous cholesterol in a dose dependent fashion. Next, an ELISA based assay using immobilized lipids was used to study binding specificities of other lipid molecules. Cholesterol was the preferred ligand of Der p 2 among 11 different lipids tested. Two homologues of Der p 2, Der f 2 and Der f 22 also bound to cholesterol. Further, using liquid chromatography-mass spectrometry (LC-MS), we confirmed that cholesterol is the natural ligand of Der p 2. Three amino acid residues of Der p 2, V104, V106 and V110 are possible cholesterol binding sites, as alanine mutations of these residues showed a significant decrease in binding (p < 0.05) compared to wild-type Der p 2. These results provide the first direct experimental evidence that Der p 2 binds to cholesterol.

Effects of Ser47-Point Mutation on Conformation Structure and Allergenicity of the Allergen of Der p 2, a Major House Dust Mite Allergen

PURPOSE

Hypoallergenic recombinant Der p 2 has been produced by various genetic manipulations, but mutation of a naturally polymorphic amino acid residue known to affect IgE binding has not been studied. This study aimed to determine the effect of a point mutation (S47W) of residue 47 of Der p 2 on its structure and immunoglobulin (Ig) E binding. Its ability to induce pro-inflammatory responses and to induce blocking IgG antibody was also determined.

METHODS

S47 of recombinant Der p 2.0110, one of the predominant variants in Bangkok, was mutated to W (S47W). S47W secreted from Pichia pastoris was examined for secondary structure and for the formation of a hydrophobic cavity by 8-Anilino-1-naphthalenesulfonic acid (ANS) staining. Monoclonal and human IgE-antibody binding was determined by enzyme-linked immunosorbent assay. Allergen-induced degranulation by human epsilon receptor expressed-rat basophil was determined. Stimulation of the pro-inflammatory cytokine interleukin (IL)-8 release from human bronchial epithelial (BEAS2B) cells and inhibition of IgE binding to the wild type allergen by S47W-induced IgG were determined.

RESULTS

S47W reduced secondary structure and failed to bind the hydrophobic ANS ligand as well as a monoclonal antibody known to be dependent on the nature of the side chain of residue 114 in an adjacent loop. It could also not stimulate IL-8 release from BEAS2B cells. IgE from house dust mite (HDM)-allergic Thais bound S47W with 100-fold weaker avidity, whereas IgE of HDM-allergic Australians did not. S47W still induced basophil degranulation, although requiring higher concentrations for some subjects. Anti-S47W antiserum-immunized mice blocked the binding of human IgE to wild type Der p 2.

CONCLUSIONS

The mutant S47W had altered structure and reduced ability to stimulate pro-inflammatory responses and to bind IgE, but retained its ability to induce blocking antibodies. It thus represents a hypoallergen produced by a single mutation of a non-solvent-accessible amino acid.

Acanthamoeba profilin elicits allergic airway inflammation in mice

Background

In previous studies, we suggested that Acanthamoeba is a new aero-allergen and that patients who showed positive results for the skin-prick test response to Acanthamoeba cross-reacted with several pollen allergens. Additionally, patients with common antibodies reacted to the 13–15 kDa Acanthamoeba unknown allergen.

Objective

We examined whether profilin of Acanthamoeba is a human airway allergic agent because of its molecular weight.

Methods

We expressed recombinant Ac-PF (rAc-PF) protein using an Escherichia coli expression system and evaluated whether Ac-PF is an airway allergic agent using an allergic airway inflammation animal model.

Results

Airway hyperresponsiveness was increased in rAc-PF-inoculated mice. The number of eosinophils and levels of Th2 cytokines, interleukin (IL)-4, IL-5, and IL-13 were increased in the bronchial alveolar lavage fluid of rAc-PF-treated mice. The lungs of the rAc-PF-treated mice group showed enhanced mucin production and metaplasia of lung epithelial cells and goblet cells.

Conclusion

In this study, we demonstrated that rAc-PF may be an allergen in Acanthamoeba, but further studies needed to identify the mechanisms of allergenic reactions induced by Ac-PF.

Recently, the number of asthma patients have increased sharply. Among patients with asthma have a high serum IgE titer, but despite this, some of these patients do not react to known allergens in skin prick tests, that suggests the presence of unknown environmental allergens. The protozoa Acanthamoeba live in very diverse environment including water, soil, air and even human nasal cavities, throat, pharynx and lung. In previous study, Acanthamoeba could be a new aero-allergen. Patients who showed positive results for the skin-prick test response to Acanthamoeba, their serum could be cross-reacted with several pollen allergens as well as Acanthamoeba total proteins. Additionally, the patients have common antibodies reacted to the 13–15 kDa Acanthamoeba unknown allergen. Profilin, which is found in all eukaryotic organisms in most cells, is an actin-binding protein that interferes with nucleation and restructuring of new filaments. Recent studies showed that profilin functions as a pan-allergen recognized by IgE in approximately 20% of birch pollen and plant food allergic patients. In Acanthamoeba, two isoforms of profilin (Ac-PF) have been identified: profilin-I and profilin-II. We examined profilin from Acanthamoeba as a potential human airway allergic agent because of its molecular weight (13–14 kDa) and cross-reactivity with several pollen allergens in the skin prick test showing positive results for Acanthamoeba in chronic cough patients. In this study, we expressed recombinant Ac-PF (rAc-PF) protein using an Escherichia coli expression system and evaluated whether Ac-PF is an airway allergic agent using an asthma animal model. Our study showed that rAc-PF may be an allergen in Acanthamoeba, but further studies needed to identify the mechanisms of allergenic reactions induced by Ac-PF.

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.

Newly designed hemagglutinin-Der p 2 chimera is a potential candidate for allergen specific immunotherapy

Aim To investigate the immunomodulatory potential of a chimera composed of the receptor-binding domain of hemagglutinin 1 (H1s) from Influenza virus and Der p 2 (D2) allergen for allergen-specific immunotherapy of house-dust mite allergy (HDM).

MAIN METHODS

H1sD2 chimera and D2 allergen were produced by genetic engineering in E. coli. Recombinant antigens were extracted from inclusion bodies by urea, then refolded and purified by immobilized- metal affinity chromatography (IMAC). Purity was verified by 2D-PAGE and secondary structures were assessed by CD spectroscopy. IgE reactivity of H1sD2 and D2 was tested in western blot with sera from 8 persons with clinical history of HDM allergy. Immunogenicity of H1sD2 and D2 were analyzed in Balb/c mice. Cytokine profile was analyzed by ELISA after stimulation of mouse spleen cells with H1sD2 and D2. Leukocyte population abundance of cells isolated from spleen and lymph node was assessed by flow cytometry.

KEY FINDINGS

Purified recombinant proteins H1sD2 (42 kDa) and D2 (15 kDa) revealed well defined secondary structures, and preserved IgE reactive epitopes. Analysis of supernatants of mouse spleen cells after stimulation with H1sD2 and D2, revealed a qualitatively different cytokine profile from H1sD2 immunized mouse cells (increase in IL10). CD8+ cells were decreased in the lymph node of D2 immunized mice, whereas H1sD2 immunization led to an increase of CD8+ cells in both the lymph node and the spleen.

SIGNIFICANCE

H1sD2 chimera attenuates Der p 2-inherent Th2 response and directs the immune response toward Th1 and Treg phenotype.

Characterization of Der f 22 - a paralogue of the major allergen Der f 2

We previously identified an expressed sequence tag clone, Der f 22, showing 41% amino acid identity to published Der f 2, and show that both genes are possible paralogues. The objective of this study was to characterize the genomic, proteomic and immunological functions Der f 22 and Der f 2. The full-length sequence of Der f 2 and Der f 22 coded for mature proteins of 129 and 135 amino acids respectively, both containing 6 cysteine residues. Phylogenetic analysis of known group 2 allergens and their homologues from our expressed sequence tag library showed that Der f 22 is a paralogue of Der f 2. Both Der f 2 and Der f 22 were single gene products with one intron. Both allergens showed specific IgE-binding to over 40% of the atopic patients, with limited of cross-reactivity. Both allergens were detected at the gut region of D. farinae by immunostaining. Der f 22 is an important allergen with significant IgE reactivity among the atopic population, and should be considered in the diagnostic panel and evaluated as future hypoallergen vaccine therapeutic target.

Conformational IgE Epitope Mapping of Der p 2 and the Evaluations of Two Candidate Hypoallergens for Immunotherapy

Epitope mapping of Der p 2, a clinically important dust-mite allergen is the first step in designing immunotherapy hypoallergen vaccine candidates. Twenty-one single alanine mutants of Der p 2 were generated and their secondary structure was analysed using circular dichroism spectra. Only one mutant, K96A resulted in a misfolded protein. All mutants were tested for serum IgE reactivity using serum from dust mite allergic individuals by immuno dot-blots. Mutations to five residues, N10, E25, K77, K96 and E102 consistently showed reduced IgE reactions compared to wild-type Der p 2, and therefore these residues constitute the major IgE epitopes of Der p 2. Two mutants with consistent low IgE binding, K96A and E102A, were subsequently evaluated as hypoallergen candidates. IgG antibodies raised in mice against both mutants could inhibit human IgE-binding to WT Der p 2. Both mutants had intact T-cell epitopes as they were able to stimulate peripheral blood mononuclear cell proliferation similar to WT Der p 2. However, a switch in Th1:Th2 cytokine profile was not observed. In summary, we have identified the major conformational epitopes of Der p 2, and evaluated two Der p 2 hypoallergen vaccine candidates for immunotherapy.

Characterization of a hybrid protein designed with segments of allergens from Blomia tropicalis and Dermatophagoides pteronyssinus

BACKGROUND

Sensitization to allergens of the house dust mites Dermatophagoides pteronyssinnus and Blomia tropicalis is an important risk factor for asthma and allergic diseases. Allergen-specific immunotherapy is currently based on natural allergen extracts, however, in the last years recombinant allergens with different modifications have shown promising immunological properties that may be advantageously applied for developing novel allergy vaccines.

METHODS

A hybrid molecule (MAVAC-BD-2) containing epitopes of B. tropicalis (Blo t 5, Blo t 8 and Blo t 10) and D. pteronyssinus (Der p 1, Der p 2, Der p 7 and Der p 8) allergens was constructed, expressed in Escherichia coli and purified by affinity chromatography. Its folding was analyzed by circular dichroism. Antibody reactivities were evaluated by ELISA and non-denaturing dot blot assays using a battery of sera from mite allergic patients and non-allergic subjects. ELISA inhibition and dot blot assays with monoclonal antibodies were used to detect B-cell epitopes. Human basophil activation and induction of IgG-blocking antibodies in mice immunized with the hybrid protein were also evaluated.

RESULTS

MAVAC-BD-2, expressed as a 22.8 kDa protein, showed a lower frequency and strength of IgE reactivity compared to Blo t 5, Der p 1, Der p 2 and the extracts of B. tropicalis and D. pteronyssinus. MAVAC-BD-2 inhibited 26% of IgE reactivity to Der p 2 and Blo t 5, reacted with anti-Der p 1 and anti-Der p 2 monoclonal antibodies and did not induce relevant basophil activation. MAVAC-BD-2 immunized mice produced specific antibodies that reacted against mite extracts and the purified allergens, as well as IgG antibodies that blocked the human IgE reactivity to mite extracts.

CONCLUSION

MAVAC-BD-2 has hypoallergenic characteristics and in mice induces IgG antibodies that block the human IgE reactivity to mite extracts.

Contributions and Future Directions for Structural Biology in the Study of Allergens

Allergy is defined as an inappropriate immune response to something normally considered harmless. The symptomatic immune response is driven by IgE antibodies directed against allergens. The study of allergens has contributed significantly to our understanding of allergic disease in 3 main areas. First, identifying allergens as the cause of symptoms and developing allergen standards has led to many advances in exposure assessment and patient diagnostics. Second, a biochemical understanding of allergens has suggested a number of hypotheses related to the mechanisms of allergic sensitization. And finally, studies of allergen-antibody interactions have contributed to understanding the cross-reactivity of allergens, mapping patient epitopes, and the development of hypoallergens. In this review, a few select cases are highlighted where structural biology, in particular, has contributed significantly to allergen research and provided new avenues for investigation.

Comparing Proteolytic Fingerprints of Antigen-Presenting Cells during Allergen Processing

Endolysosomal processing has a critical influence on immunogenicity as well as immune polarization of protein antigens. In industrialized countries, allergies affect around 25% of the population. For the rational design of protein-based allergy therapeutics for immunotherapy, a good knowledge of T cell-reactive regions on allergens is required. Thus, we sought to analyze endolysosomal degradation patterns of inhalant allergens. Four major allergens from ragweed, birch, as well as house dust mites were produced as recombinant proteins. Endolysosomal proteases were purified by differential centrifugation from dendritic cells, macrophages, and B cells, and combined with allergens for proteolytic processing. Thereafter, endolysosomal proteolysis was monitored by protein gel electrophoresis and mass spectrometry. We found that the overall proteolytic activity of specific endolysosomal fractions differed substantially, whereas the degradation patterns of the four model allergens obtained with the different proteases were extremely similar. Moreover, previously identified T cell epitopes were assigned to endolysosomal peptides and indeed showed a good overlap with known T cell epitopes for all four candidate allergens. Thus, we propose that the degradome assay can be used as a predictor to determine antigenic peptides as potential T cell epitopes, which will help in the rational design of protein-based allergy vaccine candidates.

Antigenic Determinants of Der p 1: Specificity and Cross-Reactivity Associated with IgE Antibody Recognition

Der p 1 and Der f 1 are major allergens from Dermatophagoides pteronyssinus and D. farinae, respectively. An analysis of antigenic determinants on both allergens was performed by site-directed mutagenesis. The analysis was based on the x-ray crystal structures of the allergens in complex with Fab fragments of three murine mAbs that interfere with IgE Ab binding: the two Der p 1-specific mAbs 5H8 and 10B9, and the cross-reactive mAb 4C1. On one hand, selected residues in the epitopes for mAb 5H8 and mAb 4C1 were substituted with amino acids that resulted in impaired Ab binding to Der p 1. On the other hand, an epitope for the Der p 1-specific mAb 10B9, which partially overlaps with mAb 4C1, was created in Der f 1. The mutation of 1-3 aa residues in Der f 1 was sufficient to bind mAb 10B9. These residues form hydrogen bonds with CDRs of the Ab other than H CDR3. This observation unveils an exception to the dominant role of H CDR3 commonly observed in Ag recognition. Overall, this study resulted in the identification of important residues for mAb and IgE Ab recognition in group 1 mite allergens. This information can be used to engineer allergen mutants with reduced IgE Ab binding for immunotherapy.

Proteomic analysis of castor bean tick Ixodes ricinus: a focus on chemosensory organs

In arthropods, the large majority of studies on olfaction have been focused on insects, where most of the proteins involved have been identified. In particular, chemosensing in insects relies on two families of membrane receptors, olfactory/gustatory receptors (ORs/GRs) and ionotropic receptors (IRs), and two classes of soluble proteins, odorant-binding proteins (OBPs) and chemosensory proteins (CSPs). In other arthropods, such as ticks and mites, only IRs have been identified, while genes encoding for OBPs and CSPs are absent. A third class of soluble proteins, called Niemann-Pick C2 (NPC2) has been suggested as potential carrier for semiochemicals both in insects and other arthropods. Here we report the results of a proteomic analysis on olfactory organs (Haller's organ and palps) and control tissues of the tick Ixodes ricinus, and of immunostaining experiments targeting NPC2s. Adopting different extraction and proteomic approaches, we identified a large number of proteins, and highlighted those differentially expressed. None of the 13 NPC2s known for this species was found. On the other hand, using immunocytochemistry, we detected reaction against one NPC2 in the Haller's organ and palp sensilla. We hypothesized that the low concentration of such proteins in the tick's tissues could possibly explain the discrepant results. In ligand-binding assays the corresponding recombinant NPC2 showed good affinity to the fluorescent probe N-phenylnaphthylamine and to few organic compounds, supporting a putative role of NPC2s as odorant carriers.

Evolution and predictive value of IgE responses toward a comprehensive panel of house dust mite allergens during the first 2 decades of life

BACKGROUND

The evolution of the IgE response to the numerous allergen molecules of Dermatophagoides pteronyssinus is still unknown.

OBJECTIVES

We sought to characterize the evolutionary patterns of the IgE response to 12 molecules of D pteronyssinus from birth to adulthood and to investigate their determinants and clinical relevance.

METHODS

We investigated the clinical data and sera of 722 participants in the German Multicenter Allergy Study, a birth cohort started in 1990. Diagnoses of current allergic rhinitis (AR) related to mite allergy and asthma were based on yearly interviews at the ages of 1 to 13 years and 20 years. IgE to the extract and 12 molecules of D pteronyssinus were tested by means of ImmunoCAP and microarray technology, respectively, in sera collected at ages 1, 2, 3, 5, 6, 7, 10, 13, and 20 years. Exposure to mites at age 6 and 18 months was assessed by measuring Der p 1 weight/weight concentration in house dust.

RESULTS

One hundred ninety-one (26.5%) of 722 participants ever had IgE to D pteronyssinus extract (≥0.35 kU_A/L). At age 20 years, their IgE recognized most frequently Der p 2, Der p 1, and Der p 23 (group A molecules; prevalence, >40%), followed by Der p 5, Der p 7, Der p 4, and Der p 21 (group B molecules; prevalence, 15% to 30%) and Der p 11, Der p 18, clone 16, Der p 14, and Der p 15 (group C molecules; prevalence, <10%). IgE sensitization started almost invariably with group A molecules and expanded sequentially first to group B and finally to group C molecules. Early IgE sensitization onset, parental hay fever, and higher exposure to mites were associated with a broader polymolecular IgE sensitization pattern. Participants reaching the broadest IgE sensitization stage (ie, ABC) had significantly higher risk of mite-related AR and asthma than unsensitized participants. IgE to Der p 1 or Der p 23 at age 5 years or less predicted asthma at school age.

CONCLUSIONS

Parental hay fever and early exposure to D pteronyssinus allergens promote IgE polysensitization to several D pteronyssinus molecules, which in turn predicts current mite-related AR and current/future asthma. These results might inspire predictive algorithms and prevention strategies against the progression of IgE sensitization to mites toward AR and asthma.

Synergistic Effect of Dermatophagoides farinae and Lipopolysaccharides in Human Middle ear Epithelial Cells

Purpose

Although the concept of "one airway, one disease," which includes the middle ear space as part of the united airway is well recognized, the role of allergens in otitis media with effusion (OME) is not clearly understood. We aimed to investigate the effect of the interaction between Dermatophagoides farinae (Der f) and lipopolysaccharide (LPS) on the induction of epithelial inflammatory response in vitro.

Methods

Primary human middle ear epithelial cells were exposed to Der f, LPS, or both in different sequences, and the magnitude of the immunologic responses was compared. The mRNA expressiona of mucin (MUC) 4, 5AC, 5B, 8, GM-CSF, TNF-α, TLR4, and MD-2 were evaluated using real-time PCR. MUC levels before and after siRNA-mediated knockout of TLR4 and MD-2 were assessed. Lastly, the involved cell signaling pathway was evaluated.

Results

The expressiona of cytokines, and the MUC 4, 5AC, 5B, and 8 genes were augmented by pretreatment with Der f followed by LPS; however, reverse treatment or combined treatment did not induce the same magnitude of response. Increased MUC expression was decreased by TLR4 knockdown, but not by MD-2 knockdown. The signal intensity of MUC 8 was higher in MD-2 over-expressed cells than in those exposed to LPS only. The translocation of nuclear factor-κB was observed in cells pretreated with Der f followed by LPS.

Conclusions

When Der f treatment preceded LPS exposure, Der f and LPS acted synergistically in the induction of pro-inflammatory cytokines and the MUC gene, suggesting an important role in the development of OME in patients with concealed allergy airway sensitization.

High-level expression and purification of the major house dust mite allergen Der p 2 in Escherichia coli

Der p 2, a major allergen derived from the house dust mite Dermatophagoides pteronyssinus, is one of the most clinically relevant allergens worldwide. Recombinant Der p 2 (rDer p 2) is useful in clinical diagnosis and disease-specific immunotherapy. However, previous studies showed that Der p 2 can only be expressed in Escherichia coli (E. coli) cells as inclusion bodies, thus protein refolding is required to obtain functional products. Here we report a new method to produce biologically active Der p 2 protein in E. coli. N-terminal hexahistidine- and trigger factor (TF)-tagged Der p 2 was expressed in soluble form in E. coli and purified using a combination of chromatography processes. This procedure produced milligram-level high purity Der p 2 per liter of bacterial culture. Moreover, far-UV region circular dichroism (CD) analysis and serum specific IgE reactivity test demonstrated that the secondary structure and IgE reactivity properties of rDer p 2 produced in our study were almost identical to those of natural Der p 2 (nDer p 2). In conclusion, the method developed in this work provides a useful tool for the production of immunologically active recombinant Der p 2 for clinical applications.

Relationship between the magnitude of IgE production in mice and conformational stability of the house dust mite allergen, Der p 2

BACKGROUND

Protein antigens are degraded by endosomal protease in antigen presentation cell. T cells recognize peptides derived from antigen proteins bound to class II major histocompatibility complex molecules. We previously reported that an increase in the conformational stability of an antigen depressed its immunogenicity. However, there is little information on antigens with differences in molecular properties such as net charges and molecular weight.

METHODS

Denaturation experiments against guanidine hydrochloride. The serum IgE levels to protein antigens at 35days after the first immunization analyzed using ELISA.

RESULTS

The Der p 2 mutations in which Ile13 is mutated to Ala (I13A) and Ala122 is mutated to Ile (A122I) were shown to have lower and higher conformational stability than the wild-type, respectively, by denaturation experiments. The amount of IgE production by the less stable I13A mutant was higher and that of the stable A122I mutant was lower than that of the wild-type.

CONCLUSION

Our results suggest that the increased conformational stability of Der p 2 depressed the IgE production in mice.

GENERAL SIGNIFICANCE

These findings should provide a milestone for the engineering of allergen vaccines.

Molecular Basis of the Functional Differences between Soluble Human Versus Murine MD-2: Role of Val135 in Transfer of Lipopolysaccharide from CD14 to MD-2

Myeloid differentiation factor 2 (MD-2) is an extracellular protein, associated with the ectodomain of TLR4, that plays a critical role in the recognition of bacterial LPS. Despite high overall structural and functional similarity, human (h) and murine (m) MD-2 exhibit several species-related differences. hMD-2 is capable of binding LPS in the absence of TLR4, whereas mMD-2 supports LPS responsiveness only when mMD-2 and mTLR4 are coexpressed in the same cell. Previously, charged residues at the edge of the LPS binding pocket have been attributed to this difference. In this study, site-directed mutagenesis was used to explore the hydrophobic residues within the MD-2 binding pocket as the source of functional differences between hMD-2 and mMD-2. Whereas decreased hydrophobicity of residues 61 and 63 in the hMD-2 binding pocket retained the characteristics of wild-type hMD-2, a relatively minor change of valine to alanine at position 135 completely abolished the binding of LPS to the hMD-2 mutant. The mutant, however, retained the LPS binding in complex with TLR4 and also cell activation, resulting in a murine-like phenotype. These results were supported by the molecular dynamics simulation. We propose that the residue at position 135 of MD-2 governs the dynamics of the binding pocket and its ability to accommodate lipid A, which is allosterically affected by bound TLR4.

100 Years later: Celebrating the contributions of x-ray crystallography to allergy and clinical immunology

Current knowledge of molecules involved in immunology and allergic disease results from the significant contributions of x-ray crystallography, a discipline that just celebrated its 100th anniversary. The histories of allergens and x-ray crystallography are intimately intertwined. The first enzyme structure to be determined was lysozyme, also known as the chicken food allergen Gal d 4. Crystallography determines the exact 3-dimensional positions of atoms in molecules. Structures of molecular complexes in the disciplines of immunology and allergy have revealed the atoms involved in molecular interactions and mechanisms of disease. These complexes include peptides presented by MHC class II molecules, cytokines bound to their receptors, allergen-antibody complexes, and innate immune receptors with their ligands. The information derived from crystallographic studies provides insights into the function of molecules. Allergen function is one of the determinants of environmental exposure, which is essential for IgE sensitization. Proteolytic activity of allergens or their capacity to bind LPSs can also contribute to allergenicity. The atomic positions define the molecular surface that is accessible to antibodies. In turn, this surface determines antibody specificity and cross-reactivity, which are important factors for the selection of allergen panels used for molecular diagnosis and the interpretation of clinical symptoms. This review celebrates the contributions of x-ray crystallography to clinical immunology and allergy, focusing on new molecular perspectives that influence the diagnosis and treatment of allergic diseases.

Hierarchy and molecular properties of house dust mite allergens

The allergenic load of house dust mite allergy is largely constituted by a few proteins with a hierarchical pattern of allergenicity. The serodominant specificities are the group 1&2 and the group 23 faecal allergens. The collective IgE binding to the group 1&2 allergens can measure unequivocal HDM sensitisation better than HDM extracts although discrepancies have been found in regions with complex acarofauna suggesting a need to investigate the specificity with allergen components. The group 4, 5, 7&21 allergens that each induce responses in about 40% of subjects are mid-tier allergens accounting for most of the remaining IgE binding. Their titres are proportional to the concomitant responses to Der p1&2. Group 2 allergen variants have different antibody binding. Body proteins only occasionally induce sensitisation although a higher prevalence of binding by atopic dermatitis patients provides a new avenue of research. A broad spectrum of IgE binding has been associated with diverse symptoms but not with the severity of asthma which is associated with low IgG antibody. Some allergens such as the group 14 large lipid binding proteins and the recently described proteins Der f 24-33, need further investigation but with the cognoscence that other denominated allergens have been found to be minor sensitisers by comparative quantitative analyses. Scabies is a confounder for diagnosis with extracts, inducing cross-reactive antibodies with Der p 4&20 as is seafood allergy with cross reactivity to Der p 10 a minor HDM allergen. The HDM genome sequence can now be used to verify allelic and paralogous variations.

Unique Toll-Like Receptor 4 Activation by NAMPT/PBEF Induces NFκB Signaling and Inflammatory Lung Injury

Ventilator-induced inflammatory lung injury (VILI) is mechanistically linked to increased NAMPT transcription and circulating levels of nicotinamide phosphoribosyl-transferase (NAMPT/PBEF). Although VILI severity is attenuated by reduced NAMPT/PBEF bioavailability, the precise contribution of NAMPT/PBEF and excessive mechanical stress to VILI pathobiology is unknown. We now report that NAMPT/PBEF induces lung NFκB transcriptional activities and inflammatory injury via direct ligation of Toll-like receptor 4 (TLR4). Computational analysis demonstrated that NAMPT/PBEF and MD-2, a TLR4-binding protein essential for LPS-induced TLR4 activation, share ~30% sequence identity and exhibit striking structural similarity in loop regions critical for MD-2-TLR4 binding. Unlike MD-2, whose TLR4 binding alone is insufficient to initiate TLR4 signaling, NAMPT/PBEF alone produces robust TLR4 activation, likely via a protruding region of NAMPT/PBEF (S402-N412) with structural similarity to LPS. The identification of this unique mode of TLR4 activation by NAMPT/PBEF advances the understanding of innate immunity responses as well as the untoward events associated with mechanical stress-induced lung inflammation.