Recombinant Der p 1 and Der f 1 with in vitro enzymatic activity to cleave human CD23, CD25 and alpha1-antitrypsin, and in vivo IgE-eliciting activity in mice

NLRP3 promotes allergic responses to birch pollen extract in a model of intranasal sensitization

Introduction & Objective

Allergic sensitization is an essential step in the development of allergic airway inflammation to birch pollen (BP); however, this process remains to be fully elucidated. Recent scientific advances have highlighted the importance of the allergen context. In this regard, microbial patterns (PAMPs) present on BP have attracted increasing interest. As these PAMPs are recognized by specialized pattern recognition receptors (PRRs), this study aims at investigating the roles of intracellular PRRs and the inflammasome regulator NLRP3.

Methods

We established a physiologically relevant intranasal and adjuvant-free sensitization procedure to study BP-induced systemic and local lung inflammation.

Results

Strikingly, BP-sensitized Nlrp3-deficient mice showed significantly lower IgE levels, Th2-associated cytokines, cell infiltration into the lung, mucin production and epithelial thickening than their wild-type counterparts, which appears to be independent of inflammasome formation. Intriguingly, bone-marrow chimera revealed that expression of NLRP3 in the hematopoietic system is required to trigger an allergic response.

Conclusion

Overall, this study identifies NLRP3 as an important driver of BP-induced allergic immune responses.

The New Paradigm: The Role of Proteins and Triggers in the Evolution of Allergic Asthma

Epithelial barrier damage plays a central role in the development and maintenance of allergic inflammation. Rises in the epithelial barrier permeability of airways alter tissue homeostasis and allow the penetration of allergens and other external agents. Different factors contribute to barrier impairment, such as eosinophilic infiltration and allergen protease action-eosinophilic cationic proteins' effects and allergens' proteolytic activity both contribute significantly to epithelial damage. In the airways, allergen proteases degrade the epithelial junctional proteins, allowing allergen penetration and its uptake by dendritic cells. This increase in allergen-immune system interaction induces the release of alarmins and the activation of type 2 inflammatory pathways, causing or worsening the main symptoms at the skin, bowel, and respiratory levels. We aim to highlight the molecular mechanisms underlying allergenic protease-induced epithelial barrier damage and the role of immune response in allergic asthma onset, maintenance, and progression. Moreover, we will explore potential clinical and radiological biomarkers of airway remodeling in allergic asthma patients.

Antigen Protease Activity on Intact or Tape-Stripped Skin Induces Acute Itch and T Helper Sensitization Leading to Airway Eosinophilia in Mice

Respiratory allergen sources such as house dust mites frequently contain proteases. In this study, we demonstrated that the epicutaneous application of a model protease antigen, papain, onto intact or tape-stripped ear skin of mice induced acute scratching behaviors and T helper (Th)2, Th9, Th17/Th22, and/or Th1 sensitization in a protease activity-dependent manner. The protease activity of papain applied onto the skin was also essential for subsequent airway eosinophilia induced by an intranasal challenge with low-dose papain. With tape stripping, papain-treated mice showed barrier dysfunction, the accelerated onset of acute scratching behaviors, and attenuated Th17/Th22 sensitization. In contrast, the protease activity of inhaled papain partially or critically contributed to airway atopic march responses in mice sensitized through intact or tape-stripped skin, respectively. These results indicated that papain protease activity on epicutaneous application through intact skin or skin with mechanical barrier damage is critical to the sensitization phase responses, including acute itch and Th sensitization and progression to the airway atopic march, whereas dependency on the protease activity of inhaled papain in the atopic march differs by the condition of the sensitized skin area. This study suggests that exogenous protease-dependent epicutaneous mechanisms are a target for controlling allergic sensitization and progression to the atopic march.

Protease allergens as initiators-regulators of allergic inflammation

Tremendous progress in the last few years has been made to explain how seemingly harmless environmental proteins from different origins can induce potent Th2-biased inflammatory responses. Convergent findings have shown the key roles of allergens displaying proteolytic activity in the initiation and progression of the allergic response. Through their propensity to activate IgE-independent inflammatory pathways, certain allergenic proteases are now considered as initiators for sensitization to themselves and to non-protease allergens. The protease allergens degrade junctional proteins of keratinocytes or airway epithelium to facilitate allergen delivery across the epithelial barrier and their subsequent uptake by antigen-presenting cells. Epithelial injuries mediated by these proteases together with their sensing by protease-activated receptors (PARs) elicit potent inflammatory responses resulting in the release of pro-Th2 cytokines (IL-6, IL-25, IL-1β, TSLP) and danger-associated molecular patterns (DAMPs; IL-33, ATP, uric acid). Recently, protease allergens were shown to cleave the protease sensor domain of IL-33 to produce a super-active form of the alarmin. At the same time, proteolytic cleavage of fibrinogen can trigger TLR4 signaling, and cleavage of various cell surface receptors further shape the Th2 polarization. Remarkably, the sensing of protease allergens by nociceptive neurons can represent a primary step in the development of the allergic response. The goal of this review is to highlight the multiple innate immune mechanisms triggered by protease allergens that converge to initiate the allergic response.

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.

Epicutaneous vaccination with protease inhibitor-treated papain prevents papain-induced Th2-mediated airway inflammation without inducing Th17 in mice

Environmental allergen sources such as house dust mites contain proteases, which are frequently allergens themselves. Inhalation with the exogenous proteases, such as a model of protease allergen, papain, to airways evokes release and activation of IL-33, which promotes innate and adaptive allergic airway inflammation and Th2 sensitization in mice. Here, we examine whether epicutaneous (e.c.) vaccination with antigens with and without protease activity shows prophylactic effect on the Th airway sensitization and Th2-medated airway inflammation, which are driven by exogenous or endogenous IL-33. E.c. vaccination with ovalbumin restrained ovalbumin-specific Th2 airway sensitization and/or airway inflammation on subsequent inhalation with ovalbumin plus papain or ovalbumin plus recombinant IL-33. E.c. vaccination with papain or protease inhibitor-treated papain restrained papain-specific Th2 and Th9 airway sensitization, eosinophilia, and infiltration of IL-33-responsive Th2 and group 2 innate lymphoid cells on subsequent inhalation with papain. However, e.c. vaccination with papain but not protease inhibitor-treated papain induced Th17 response in bronchial draining lymph node cells. In conclusions, we demonstrated that e.c. allergen vaccination via intact skin in mice restrained even protease allergen-activated IL-33-driven airway Th2 sensitization to attenuate allergic airway inflammation and that e.c. vaccination with protease allergen attenuated the airway inflammation similar to its derivative lacking the protease activity, although the former but not the latter promoted Th17 development. In addition, the present study suggests that modified allergens, of which Th17-inducing e.c. adjuvant activity such as the protease activity was eliminated, might be preferable for safer clinical applications of the e.c. allergen administration.

Degradation of bacterial permeability family member A1 (BPIFA1) by house dust mite (HDM) cysteine protease Der p 1 abrogates immune modulator function

Bacterial permeability family member A1 (BPIFA1) is one of the most abundant proteins present in normal airway surface liquid (ASL). It is known to be diminished in asthmatic patients' sputum, which causes airway hyperresponsiveness (AHR). What is currently unclear is how environmental factors, such as allergens' impact on BPIFA1's abundance and functions in the context of allergic asthma. House dust mite (HDM) is a predominant domestic source of aeroallergens. The group of proteases found in HDM is thought to cleave multiple cellular protective mechanisms, and therefore foster the development of allergic asthma. Here, we show that BPIFA1 is cleaved by HDM proteases in a time-, dose-, and temperature-dependent manner. We have also shown the main component in HDM that is responsible for BPIFA1's degradation is Der p1. Fragmented BPIFA1 failed to bind E. coli lipopolysaccharide (LPS), and hence elevated TNFα and IL-6 secretion in human whole blood. BPIFA1 degradation is also observed in vivo in bronchoalveolar fluid (BALF) of mice which are intranasally instilled with HDM. These data suggest that proteases associated with environmental allergens such as HDM cleave BPIFA1 and therefore impair its immune modulator function.

Interaction of host and Staphylococcus aureus protease-system regulates virulence and pathogenicity

Staphylococcus aureus causes various health care- and community-associated infections as well as certain chronic TH2 driven inflammatory diseases. It is a potent pathogen with serious virulence and associated high morbidity. Severe pathogenicity is accredited to the S. aureus secreted virulence factors such as proteases and host protease modulators. These virulence factors promote adhesion and invasion of bacteria through damage of tight junction barrier and keratinocytes. They inhibit activation and transmigration of various immune cells such as neutrophils (and neutrophil proteases) to evade opsono-phagocytosis and intracellular bacterial killing. Additionally, they protect the bacteria from extracellular killing by disrupting integrity of extracellular matrix. Platelet activation and agglutination is also impaired by these factors. They also block the classical as well as alternative pathways of complement activation and assist in spread of infection through blood and tissue. As these factors are exquisite factors of S. aureus mediated disease development, we have focused on review of diversification of various protease-system associated virulence factors, their structural building, diverse role in disease development and available therapeutic counter measures. This review summarises the role of protease-associated virulence factors during invasion and progression of disease.

Allergen Delivery Inhibitors: A Rationale for Targeting Sentinel Innate Immune Signaling of Group 1 House Dust Mite Allergens through Structure-Based Protease Inhibitor Design

Diverse evidence from epidemiologic surveys and investigations into the molecular basis of allergenicity have revealed that a small cadre of "initiator" allergens promote the development of allergic diseases, such as asthma, allergic rhinitis, and atopic dermatitis. Pre-eminent among these initiators are the group 1 allergens from house dust mites (HDM). In mites, group 1 allergens function as cysteine peptidase digestive enzymes to which humans are exposed by inhalation of HDM fecal pellets. Their protease nature confers the ability to activate high gain signaling mechanisms which promote innate immune responses, leading to the persistence of allergic sensitization. An important feature of this process is that the initiator drives responses both to itself and to unrelated allergens lacking these properties through a process of collateral priming. The clinical significance of group 1 HDM allergens in disease, their serodominance as allergens, and their IgE-independent bioactivities in innate immunity make these allergens interesting therapeutic targets in the design of new small-molecule interventions in allergic disease. The attraction of this new approach is that it offers a powerful, root-cause-level intervention from which beneficial effects can be anticipated by interference in a wide range of effector pathways associated with these complex diseases. This review addresses the general background to HDM allergens and the validation of group 1 as putative targets. We then discuss structure-based drug design of the first-in-class representatives of allergen delivery inhibitors aimed at neutralizing the proteolytic effects of HDM group 1 allergens, which are essential to the development and maintenance of allergic diseases.

Application of the adverse outcome pathway (AOP) concept to structure the available in vivo and in vitro mechanistic data for allergic sensitization to food proteins

BACKGROUND

The introduction of whole new foods in a population may lead to sensitization and food allergy. This constitutes a potential public health problem and a challenge to risk assessors and managers as the existing understanding of the pathophysiological processes and the currently available biological tools for prediction of the risk for food allergy development and the severity of the reaction are not sufficient. There is a substantial body of in vivo and in vitro data describing molecular and cellular events potentially involved in food sensitization. However, these events have not been organized in a sequence of related events that is plausible to result in sensitization, and useful to challenge current hypotheses. The aim of this manuscript was to collect and structure the current mechanistic understanding of sensitization induction to food proteins by applying the concept of adverse outcome pathway (AOP).

MAIN BODY

The proposed AOP for food sensitization is based on information on molecular and cellular mechanisms and pathways evidenced to be involved in sensitization by food and food proteins and uses the AOPs for chemical skin sensitization and respiratory sensitization induction as templates. Available mechanistic data on protein respiratory sensitization were included to fill out gaps in the understanding of how proteins may affect cells, cell-cell interactions and tissue homeostasis. Analysis revealed several key events (KE) and biomarkers that may have potential use in testing and assessment of proteins for their sensitizing potential.

CONCLUSION

The application of the AOP concept to structure mechanistic in vivo and in vitro knowledge has made it possible to identify a number of methods, each addressing a specific KE, that provide information about the food allergenic potential of new proteins. When applied in the context of an integrated strategy these methods may reduce, if not replace, current animal testing approaches. The proposed AOP will be shared at the www.aopwiki.org platform to expand the mechanistic data, improve the confidence in each of the proposed KE and key event relations (KERs), and allow for the identification of new, or refinement of established KE and KERs.

Allergies - A T cells perspective in the era beyond the TH1/TH2 paradigm

Allergic diseases have emerged as a major health care burden, especially in the western hemisphere. They are defined by overshooting reactions of an aberrant immune system to harmless exogenous stimuli. The T_H1/T_H2 paradigm assumes that a dominance of T_H2 cell activation and an inadequate T_H1 cell response are responsible for the development of allergies. However, the characterization of additional T helper cell subpopulations such as T_H9, T_H17, T_H22, T_HGM-CSF and their interplay with regulatory T cells suggest further layers of complexity. This review summarizes state-of-the-art knowledge on T cell diversity and their induction, while revisiting the T_H1/T_H2 paradigm. With respect to these numerous contributors, it offers a new perspective on the pathogenesis of asthma, allergic rhinitis (AR) and atopic dermatitis (AD) incorporating recent discoveries in the field of T cell plasticity.

Expression and refolding of mite allergen pro-Der f1 from inclusion bodies in Escherichia coli

House dust mite (Dermatophagoides farinae) allergen Der f1 is one of the most important indoor allergens associated with asthma, eczema and allergic rhinitis in humans. Therefore, sufficient quantities of Der f1 cysteine protease to be used for both experimental and therapeutic purposes are very much needed. Using recombinant DNA technology, high expression rates of cysteine proteases were obtained. The cDNA sequence encoding pro-Der f1 was cloned and expressed in Escherichia coli using the T7 based expression vector pET-44a and induced by isopropyl-β-d-thiogalactoside at a final concentration of 0.2mM. Recombinant pro-Der f1 (pro-rDer f1) was expressed as an inclusion body and the isolated protease was solubilized, refolded and purified. The protease activities and IgE reactivities of pro-rDer f1 that were refolded by size-exclusion chromatography (SEC) were higher than those obtained by dilution. The pair of pro-rDer f1 polypeptides produced by this method could be used for more effective and safer allergen-specific immunotherapy or to produce enzymatically and immunologically active Der f1 for diagnostic testing and deciphering of immunotherapy mechanisms.

The discovery of potent, selective, and reversible inhibitors of the house dust mite peptidase allergen Der p 1: an innovative approach to the treatment of allergic asthma

Blocking the bioactivity of allergens is conceptually attractive as a small-molecule therapy for allergic diseases but has not been attempted previously. Group 1 allergens of house dust mites (HDM) are meaningful targets in this quest because they are globally prevalent and clinically important triggers of allergic asthma. Group 1 HDM allergens are cysteine peptidases whose proteolytic activity triggers essential steps in the allergy cascade. Using the HDM allergen Der p 1 as an archetype for structure-based drug discovery, we have identified a series of novel, reversible inhibitors. Potency and selectivity were manipulated by optimizing drug interactions with enzyme binding pockets, while variation of terminal groups conferred the physicochemical and pharmacokinetic attributes required for inhaled delivery. Studies in animals challenged with the gamut of HDM allergens showed an attenuation of allergic responses by targeting just a single component, namely, Der p 1. Our findings suggest that these inhibitors may be used as novel therapies for allergic asthma.

Epicutaneous administration of papain induces IgE and IgG responses in a cysteine protease activity-dependent manner

BACKGROUND

Epicutaneous sensitization to allergens is important in the pathogenesis of not only skin inflammation such as atopic dermatitis but also "atopic march" in allergic diseases such as asthma and food allergies. We here examined antibody production and skin barrier dysfunction in mice epicutaneously administered papain, a plant-derived occupational allergen belonging to the same family of cysteine proteases as mite major group 1 allergens.

METHODS

Papain and Staphylococcus aureus V8 protease were patched on the backs of hairless mice. Transepidermal water loss was measured to evaluate the skin barrier dysfunction caused by the proteases. Papain or that treated with an irreversible inhibitor specific to cysteine proteases, E64, was painted onto the ear lobes of mice of an inbred strain C57BL/6. Serum total IgE levels and papain-specific IgE and IgG antibodies were measured by ELISA.

RESULTS

Papain and V8 protease patched on the backs of hairless mice caused skin barrier dysfunction and increased serum total IgE levels, and papain induced the production of papain-specific IgG1, IgG2a, and IgG2b. Papain painted onto the ear lobes of C57BL/6 mice induced papain-specific IgE, IgG1, IgG2c, and IgG2b, whereas papain treated with E64 did not. IgG1 was the most significantly induced papain-specific IgG subclass among those measured.

CONCLUSIONS

We demonstrated that the epicutaneous administration of protease not only disrupted skin barrier function, but also induced IgE and IgG responses in a manner dependent on its protease activity. These results suggest that protease activity contained in environmental sources contributes to sensitization through an epicutaneous route.

Acanthamoeba protease activity promotes allergic airway inflammation via protease-activated receptor 2

Acanthamoeba is a free-living amoeba commonly present in the environment and often found in human airway cavities. Acanthamoeba possesses strong proteases that can elicit allergic airway inflammation. To our knowledge, the aeroallergenicity of Acanthamoeba has not been reported. We repeatedly inoculated mice with Acanthamoeba trophozoites or excretory-secretory (ES) proteins intra-nasally and evaluated symptoms and airway immune responses. Acanthamoeba trophozoites or ES proteins elicited immune responses in mice that resembled allergic airway inflammation. ES proteins had strong protease activity and activated the expression of several chemokine genes (CCL11, CCL17, CCL22, TSLP, and IL-25) in mouse lung epithelial cells. The serine protease inhibitor phenyl-methane-sulfonyl fluoride (PMSF) inhibited ES protein activity. ES proteins also stimulated dendritic cells and enhanced the differentiation of naive T cells into IL-4-secreting T cells. After repeated inoculation of the protease-activated receptor 2 knockout mouse with ES proteins, airway inflammation and Th2 immune responses were markedly reduced, but not to basal levels. Furthermore, asthma patients had higher Acanthamoeba-specific IgE titers than healthy controls and we found Acanthamoeba specific antigen from house dust in typical living room. Our findings suggest that Acanthamoeba elicits allergic airway symptoms in mice via a protease allergen. In addition, it is possible that Acanthamoeba may be one of the triggers human airway allergic disease.

Cystatin SN upregulation in patients with seasonal allergic rhinitis

Seasonal allergic rhinitis (SAR) to the Japanese cedar, Cryptomeria japonica (JC) pollen is an IgE-mediated type I allergy affecting nasal mucosa. However, the molecular events underlying its development remain unclear. We sought to identify SAR-associated altered gene expression in nasal epithelial cells during natural exposure to JC pollen. We recruited study participants in 2009 and 2010 and collected nasal epithelial cells between February and April, which is the period of natural pollen dispersion. Fifteen patients with SAR-JC and 13 control subjects were enrolled in 2009, and 17 SAR-JC patients, 13 sensitized asymptomatic subjects (Sensitized), and 15 control subjects were enrolled in 2010. Total RNA was extracted from nasal epithelial cells and 8 SAR-JC patients and 6 control subjects in 2009 were subjected to microarray analysis with the Illumina HumanRef-8 Expression BeadChip platform. Allergen-stimulated histamine release was examined in the peripheral blood basophils isolated from patients with SAR. We identified 32 genes with significantly altered expression during allergen exposure. One of these, CST1 encodes the cysteine protease inhibitor, cystatin SN. CST1 expression in nasal epithelial cells was significantly upregulated in both the 2009 and 2010 SAR-JC groups compared with the control groups. Immunohistochemical staining confirmed the increased expression of CST1 in the nasal epithelial cells of SAR patients. Addition of exogenous CST1 to basophils inhibited JC allergen-stimulated histamine release in vitro. We propose that CST1 may contribute to inactivation of protease allergens and help re-establish homeostasis of the nasal membranes.

IL-33-mediated innate response and adaptive immune cells contribute to maximum responses of protease allergen-induced allergic airway inflammation

How the innate and adaptive immune systems cooperate in the natural history of allergic diseases has been largely unknown. Plant-derived allergen, papain, and mite allergens, Der f 1 and Der p 1, belong to the same family of cysteine proteases. We examined the role of protease allergens in the induction of Ab production and airway inflammation after repeated intranasal administration without adjuvants and that in basophil/mast cell stimulation in vitro. Papain induced papain-specific IgE/IgG1 and lung eosinophilia. Der f 1 induced Der f 1-specific IgG1 and eosinophilia. Although papain-, Der f 1-, and Der p 1-stimulated basophils expressed allergy-inducing cytokines, including IL-4 in vitro, basophil-depleting Ab and mast cell deficiency did not suppress the papain-induced in vivo responses. Protease inhibitor-treated allergens and a catalytic site mutant did not induce the responses. These results indicate that protease activity is essential to Ab production and eosinophilia in vivo and basophil activation in vitro. IL-33-deficient mice lacked eosinophilia and had reduced papain-specific IgE/IgG1. Coadministration of OVA with papain induced OVA-specific IgE/IgG1, which was reduced in IL-33-deficient mice. We demonstrated IL-33 release, subsequent IL-33-dependent IL-5/IL-13 release, and activation of T1/ST2-expressing lineage(-)CD25(+)CD44(+) innate lymphoid cells in the lung after papain inhalation, suggesting the contribution of the IL-33-type 2 innate lymphoid cell-IL-5/IL-13 axis to the papain-induced airway eosinophilia. Rag2-deficient mice, which lack adaptive immune cells, showed significant, but less severe, eosinophilia. Collectively, these results suggest cooperation of adaptive immune cells and IL-33-responsive innate cells in protease-dependent allergic airway inflammation.

Protease-activated receptor-2 induces proinflammatory cytokine and chemokine gene expression in canine keratinocytes

Although the molecular basis of the allergenicity remains to be fully elucidated, the ability of allergens to elicit allergic responses is at least partly attributed to their proteolytic activity. Protease-activated receptor-2 (PAR-2) is a G protein-coupled receptor that is activated by site-specific proteolysis by serine proteases and is known to mediate inflammatory processes in various tissues. In this study, we investigated the effects of trypsin, a major serine protease, and a human PAR-2 agonist peptide (SLIGKV-NH2) on proinflammatory cytokine and chemokine gene expression in the canine keratinocyte cell line CPEK. The expression of PAR-2 mRNA and protein in CPEK cells was detected by RT-PCR and Western blotting, respectively. The localization of PAR-2 in CPEK was examined by immunofluorescence. The mRNA expression levels of proinflammatory cytokines and chemokines were quantified by real-time RT-PCR. The free intracellular Ca(2+) concentration was measured using the Ca(2+)-sensitive fluorescent dye. CPEK cells constitutively expressed PAR-2 mRNA and protein. Stimulation of CPEK cells with trypsin induced significant upregulation of the mRNA expression levels of tumor necrosis factor alpha (TNF-α, P<0.05), granulocyte-macrophage colony-stimulating factor (GM-CSF, P<0.01), thymus and activation regulated chemokine (TARC/CCL17, P<0.01), and interleukin 8 (IL-8/CXCL8, P<0.01). Similarly, the PAR-2 agonist peptide increased the mRNA expression levels of TNF-α (P<0.05), GM-CSF (P<0.05), TARC/CCL17 (P<0.05), and IL-8/CXCL8 (P<0.05) in CPEK cells. Both trypsin and the PAR-2 agonist peptide increased the intracellular Ca(2+) concentration and PAR-2 internalization. These results suggest that PAR-2 activation can augment inflammatory cytokine and chemokine expression in canine keratinocytes, and it may initiate allergic inflammation through the proteolytic activity of allergens in canine atopic dermatitis.

Analysis of properties and proinflammatory functions of cockroach allergens Per a 1.01s

Cockroaches have been identified as one of the major indoor allergens inducing perennial rhinitis and asthma. Per a 1s are a group of the major allergens from American cockroach. Although Per a 1s are major allergens from American cockroach, factors contributing to the allergenicity of Per a 1s are still poorly defined. To investigate the effects of Per a 1s on the expression of PARs and the release of proinflammatory cytokines from mast cells. Per a 1.0101 and Per a 1.0104 were cloned from American cockroach and then expressed in Eschericia coli. The purified allergens were used to stimulate P815 mast cells, and the expression of protease-activated receptors (PARs) was determined by real-time RT-PCR and flow cytometry. The levels of IL-4 and IL-13 in culture media were detected with ELISA. Sera from 80 and 77.3% of cockroach allergy patients reacted to recombinant Per a (rPer a) 1.0101 and rPer a 1.0104, confirming they are major allergens. Both rPer a 1.0101 and rPer a 1.0104 had no enzymatic activity, but rPer a 1.0101 upregulated the expression of PAR-1 and PAR-2, and rPer a 1.0104 enhanced the expression of PAR-1 and PAR-4 proteins. Both recombinant allergens were able to increase the release of IL-4 and IL-13 from P815 mast cells. This is the first study aiming to investigate functions of group 1 allergens of American cockroach. rPer a 1.0101 and rPer a 1.0104 have the capacity to upregulate the expression of PARs and to enhance Th2 cytokine production in mast cells.

Marasmius oreades agglutinin (MOA) is a chimerolectin with proteolytic activity

The Marasmius oreades mushroom lectin (MOA) is well known for its exquisite binding specificity for blood group B antigens. In addition to its N-terminal carbohydrate-binding domain, MOA possesses a C-terminal domain with unknown function, which structurally resembles hydrolytic enzymes. Here we show that MOA indeed has catalytic activity. It is a calcium-dependent cysteine protease resembling papain-like cysteine proteases, with Cys215 being the catalytic nucleophile. The possible importance of MOA's proteolytic activity for mushroom defense against pathogens is discussed.

[House dust mites allergens]

INTRODUCTION

House dust mite allergens from the Pyroglyphidae family are one of the most frequent and potent causes of allergic sensitatisation. Since 1988, molecular knowledge has increased considerably and structures and functions have been determined for most of them.

BACKGROUND

Of the 22 defined allergens, the major IgE-binding has been reported for groups 1 and 2 accounting for 40-60% of the anti-house dust mite titres. Der p 1, 2, 4, 5, 7 allergens account for about 80% of the IgE-response. Der p 4, 5, 7, 11, 14, 15 have a prevalence of sensitization of about 10% each. The IgE-binding to groups 3, 8, 10, 20 is low. Most of the allergens can be identified by amino-acid sequences and the tertiary structures of the major allergens have been solved. Most allergens are proteolytic enzymes: Der p1 for instance is a cysteine protease. Der p 2 has structural homology with MD-2, a co-receptor of the Toll-like receptor (TLR4) whose ligand is LPS. Knowledge of the structure of mite allergens has allowed better interpretation of cross-reactions between allergens from the same family or from more distant families.

CONCLUSIONS

From a practical point of view: the occurrence of multisensitisation is better explained and molecular epidemiology has allowed a better choice of allergen molecules useful for diagnosis. Finally, new concepts of immunotherapy based on genetically engineered hypoallergenic variants of major allergens, used alone or in combination, may lead to useful therapeutic approach.

Barrier dysfunction caused by environmental proteases in the pathogenesis of allergic diseases

Skin barrier dysfunction has emerged as a critical driving force in the initiation and exacerbation of atopic dermatitis and the "atopic march" in allergic diseases. The genetically determined barrier deficiency and barrier disruption by environmental and endogenous proteases in skin and epithelium are considered to increase the risk of sensitization to allergens and contribute to the exacerbation of allergic diseases. Sources of allergens such as mites, cockroaches, fungi, and pollen, produce or contain proteases, which are frequently themselves allergens. Staphylococcus aureus, which heavily colonizes the lesions of atopic dermatitis patients and is known to trigger a worsening of the disease, also produces extracellular proteases. Environmental proteases can cause barrier breakdown in the skin, not only in the epithelium, and stimulate various types of cells through IgE-independent mechanisms. Endogenous protease inhibitors control the functions of environmental and endogenous proteases. In this review, we focus on the barrier dysfunction caused by environmental proteases and roles of endogenous protease inhibitors in the pathogenesis of allergic diseases. Additionally, we examine the subsequent innate response to Th2-skewed adaptive immune reactions.

Interactions of airway epithelium with protease allergens in the allergic response

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

Cupressaceae pollen grains modulate dendritic cell response and exhibit IgE-inducing adjuvant activity in vivo

Pollen is considered a source of not only allergens but also immunomodulatory substances, which could play crucial roles in sensitization and/or the exacerbation of allergies. We investigated how allergenic pollens from different plant species (Japanese cedar and Japanese cypress, which belong to the Cupressaceae family, and birch, ragweed, and grass) modulate murine bone marrow-derived dendritic cell (DC) responses and examined the effect of Cupressaceae pollen in vivo using mice. DCs were stimulated with pollen extracts or grains in the presence or absence of LPS. Cell maturation and cytokine production in DCs were analyzed by flow cytometry, ELISA, and/or quantitative PCR. Pollen extracts suppressed LPS-induced IL-12 production and the effect was greatest for birch and grass. Without LPS, pollen grains induced DC maturation and cytokine production without IL-12 secretion and the response, for which TLR 4 was dispensable, was greatest for the Cupressaceae family. Intranasal administration of Cupressaceae pollen in mice induced an elevation of serum IgE levels and airway eosinophil infiltration. Coadministration of ovalbumin with Cupressaceae pollen grains induced ovalbumin-specific IgE responses associated with eosinophil infiltration. The results suggest that modulation of DC responses by pollen differs among the plant families via (1) the promotion of DC maturation and cytokine production by direct contact and/or (2) the inhibition of IL-12 production by soluble factors. The strong DC stimulatory activity in vitro and IgE-inducing activity in mice support the clinical relevance of Cupressaceae pollen to allergies in humans.

Enzyme-linked immunosorbent assays with high sensitivity for antigen-specific and total murine IgE: a useful tool for the study of allergies in mouse models

BACKGROUND

In studies on allergies in mouse models, IgE production is an essential parameter to be evaluated. Here, we examine the effect of commercially available immunoreaction enhancer solutions and different blocking reagents in enzyme-linked immunosorbent assay (ELISA) for total or antigen-specific murine IgE in order to improve the assays.

METHODS

Sera from mice immunized with recombinant house dust mite major allergens, Der f 1 and Der p 1, were used for the assays. Total IgE was measured by sandwich ELISA using monoclonal antibodies against murine IgE. Antigen-specific IgE was assayed using allergen-coated plates. Sensitivity or signal intensity in ELISA was compared among conditions differing in the use of enhancer solutions, blocking reagents, or monoclonal antibodies, and incubation time.

RESULTS

Use of enhancer solutions improved the sensitivity of ELISA for total IgE by approximately 30-fold of that using a conventional buffer. A blocking reagent caused more unwanted enhancement of the background signal in blank wells in ELISA for total IgE compared with another blocking reagent, however, improved signal intensity in ELISA for antigen-specific ELISA without significant enhancement of the background signal. Optimal assay conditions were determined.

CONCLUSIONS

Enhancer solutions are effective in improving ELISAs for total and antigen-specific murine IgE. Selection of blocking reagents was important to decrease unwanted enhancement of background signals and was effective in enhancing signals for positive samples. The ELISAs improved in this study are useful for the study of allergies in mouse models.

Comparative enzymology of native and recombinant house dust mite allergen Der p 1

BACKGROUND

The cysteine peptidase activity of group 1 house dust mite allergens is important for their allergenicity and may offer new therapeutic targets for allergy treatment. Hitherto, the design of specific inhibitors has been impeded because the availability of pure, fully active allergens has limited the implementation of drug screening campaigns. Similarly, investigation of the mechanisms by which peptidase allergens promote sensitization has also been restricted. Our aim was to compare the enzymology of recombinant and native forms of Der p 1 to establish if an easily expressed recombinant form of Der p 1 could be used as a drug discovery tool.

METHODS

Enzymatic activity of natural and recombinant Der p 1 was compared fluorimetrically using a novel specific substrate (ADZ 50,059) and a novel specific active site titrant (ADZ 50,000). The effect of recombinant Der p 1 prodomain on the catalytic activity of both Der p 1 preparations was also examined.

RESULTS

Although differing substantially in molecular weight, the enzymological properties of recombinant and native Der p 1 were indistinguishable. Our data show clearly by experiment that, in contrast to some suggestions, Der p 1 is not an enzyme of bifunctional mechanism.

CONCLUSION

The catalytic activity of Der p 1 is tolerant of glycosylation differences that occur at N150 when the protein is expressed in Pichia pastoris. This suggests that this recombinant protein may be suitable for drug design studies and in the elucidation of how peptidase activity promotes sensitization to peptidase and nonpeptidase bystander allergens.

Dectin-2 recognition of house dust mite triggers cysteinyl leukotriene generation by dendritic cells

House dust mites are a significant source of airborne allergen worldwide, but there is little understanding of how they so potently generate allergic inflammation. We found that extracts from the house dust mites Dermatophagoides farinae (Df) and Dermatophagoides pteronyssinus and from the mold Aspergillus fumigatus stimulated a rapid and robust production of cysteinyl leukotrienes (cys-LTs), proinflammatory lipid mediators, from mouse bone marrow-derived dendritic cells (BMDCs). Con A affinity chromatography of the Df extract revealed that the relevant ligand is a glycan(s), suggesting stimulation via a dendritic cell (DC) lectin receptor. Cys-LT production in BMDCs from wild-type mice was inhibited by spleen tyrosine kinase (Syk) inhibitors and was abolished in BMDCs from FcRgamma-/- mice, implicating either Dectin-2 or DC immunoactivating receptor. Transfection of each receptor in bone marrow-derived mast cells revealed that only Dectin-2 mediates cys-LT production by Df, Dermatophagoides pteronyssinus, and Aspergillus fumigatus. Lentiviral knockdown of Dectin-2 in BMDCs attenuated Df extract-elicited cys-LT generation, thereby identifying Dectin-2 as the receptor. Lung CD11c+ cells, but not peritoneal or alveolar macrophages, also generated cys-LTs in response to Df. These findings place Dectin-2 among the C-type lectin receptors that activate arachidonic acid metabolism and identify the Dectin-2/FcRgamma/Syk/cys-LT axis as a novel mechanism by which three potent indoor allergens may activate innate immune cells to promote allergic inflammation.

Determinants of allergenicity

The question "What makes an allergen an allergen?" has puzzled generations of researchers, and we still do not have a conclusive answer. Despite increasing knowledge about the molecular and functional characteristics of allergens that have been identified, we still do not fully understand why some proteins are clinically relevant allergens and most are not. Different approaches have been taken to identify the structural and functional features of allergens, aiming at developing methods to predict allergenicity and thus to identify allergens. However, none of these methods has allowed a reliable discrimination between allergenic and nonallergenic compounds on its own. This review sums up diverse determinants that contribute to the phenomenon of allergenicity and outlines that in addition to the structure and function of the allergen, factors derived from allergen carriers, the environment, and the susceptible individual are of importance.

Anisakis simplex: from obscure infectious worm to inducer of immune hypersensitivity

Infection of humans with the nematode worm parasite Anisakis simplex was first described in the 1960s in association with the consumption of raw or undercooked fish. During the 1990s it was realized that even the ingestion of dead worms in food fish can cause severe hypersensitivity reactions, that these may be more prevalent than infection itself, and that this outcome could be associated with food preparations previously considered safe. Not only may allergic symptoms arise from infection by the parasites ("gastroallergic anisakiasis"), but true anaphylactic reactions can also occur following exposure to allergens from dead worms by food-borne, airborne, or skin contact routes. This review discusses A. simplex pathogenesis in humans, covering immune hypersensitivity reactions both in the context of a living infection and in terms of exposure to its allergens by other routes. Over the last 20 years, several studies have concentrated on A. simplex antigen characterization and innate as well as adaptive immune response to this parasite. Molecular characterization of Anisakis allergens and isolation of their encoding cDNAs is now an active field of research that should provide improved diagnostic tools in addition to tools with which to enhance our understanding of pathogenesis and controversial aspects of A. simplex allergy. We also discuss the potential relevance of parasite products such as allergens, proteinases, and proteinase inhibitors and the activation of basophils, eosinophils, and mast cells in the induction of A. simplex-related immune hypersensitivity states induced by exposure to the parasite, dead or alive.

Upregulation of the release of granulocyte-macrophage colony-stimulating factor from keratinocytes stimulated with cysteine protease activity of recombinant major mite allergens, Der f 1 and Der p 1

BACKGROUND

Although exposure to mite allergens is an important risk factor for the production of IgE and is associated with various allergic diseases, there has been uncertainty as to the route of exposure by which sensitization occurs. Cystatin A is a skin-derived dominant inhibitor against proteolytic activity of major mite allergens, Der f 1 and Der p 1, and blocks the upregulation of IL-8 release from human keratinocytes stimulated with the allergens. We analyzed whether the stimulation of keratinocytes with the allergens upregulates the release of granulocyte-macrophage colony-stimulating factor (GM-CSF), which has many actions relevant to allergic diseases including atopic dermatitis, and if so, whether cystatin A can block this process.

METHODS

Normal human keratinocytes and the human keratinocyte cell line HaCaT were stimulated with recombinant group 1 allergens in the absence or presence of cystatin A.

RESULTS

Stimulation with the recombinant allergens upregulated the release of GM-CSF from normal human keratinocytes in a culture with high calcium concentration and HaCaT cells, which could be inhibited by the addition of cystatin A. The allergens exhibiting proteolytic activity did not digest cystatin A. Proteolytic activity of recombinant Der f 1 was partially regenerated after incubation with keratinocytes even without preactivation by L-cysteine.

CONCLUSION

Proteolytic activity of recombinant Der f 1 and Der p 1 upregulates GM-CSF and IL-8 release from keratinocytes in vitro, suggesting possible contributions to sensitization through the skin and the perpetuation of atopic dermatitis, as well as a homeostatic role for cystatin A against inflammation of the skin.

Interactions between mature Der p 1 and its free prodomain indicate membership of a new family of C1 peptidases

BACKGROUND

Studies in vivo have shown that the cysteine peptidase activity of group 1 house dust mite allergens contributes to their allergenicity. These allergens are synthesized initially as proenzymes and removal of the propiece is necessary to unmask their proteolytic activity. In related C1 family cysteine peptidases of enzyme clan CA, liberated propieces continue to inhibit the mature peptidase as tight binding inhibitors. As it is not known whether mite peptidase allergens behave similarly, our objective was to investigate the effect of the Der p 1 propiece on the catalytic activity of Der p 1 and Der f 1.

METHODS

Enzymatic activity of natural Der p 1 and Der f 1 was assessed using a specific substrate and the effect of the recombinant propiece on its enzyme kinetics defined. The integrity of the propiece during these interactions was studied functionally and by analysis of the reaction mixtures.

RESULTS

Der p 1 propiece was a potent competitive inhibitor of Der p 1 and Der f 1. In contrast to other cysteine peptidase prodomains, which are cognate tight binding inhibitors, the Der p 1 propiece behaves as a substrate and is fully degraded during this interaction.

CONCLUSION

Mature Der p 1-prodomain interactions differ from other C1 family cysteine peptidases, suggesting that group 1 mite allergens are a new subgroup among C1 family cysteine peptidases. The rapid inactivation of Der p 1 prodomain is a newly identified mechanism that may contribute to the potency of this allergen.

Major house dust mite allergens Dermatophagoides pteronyssinus 1 and Dermatophagoides farinae 1 degrade and inactivate lung surfactant proteins A and D

Lung surfactant proteins (SP) A and D are calcium-dependent carbohydrate-binding proteins. In addition to playing multiple roles in innate immune defense such as bacterial aggregation and modulation of leukocyte function, SP-A and SP-D have also been implicated in the allergic response. They interact with a wide range of inhaled allergens, competing with their binding to cell-sequestered IgE resulting in inhibition of mast cell degranulation, and exogenous administration of SP-A and SP-D diminishes allergic hypersensitivity in vivo. House dust mite allergens are a major cause of allergic asthma in the western world, and here we confirm the interaction of SP-A and SP-D with two major mite allergens, Dermatophagoides pteronyssinus 1 and Dermatophagoides farinae 1, and show that the cysteine protease activity of these allergens results in the degradation of SP-A and SP-D under physiological conditions, with multiple sites of cleavage. A recombinant fragment of SP-D that is effective in diminishing allergic hypersensitivity in mouse models of dust mite allergy was more susceptible to degradation than the native full-length protein. Degradation was enhanced in the absence of calcium, with different sites of cleavage, indicating that the calcium associated with SP-A and SP-D influences accessibility to the allergens. Degradation of SP-A and SP-D was associated with diminished binding to carbohydrates and to D. pteronyssinus 1 itself and diminished capacity to agglutinate bacteria. Thus, the degradation and consequent inactivation of SP-A and SP-D may be a novel mechanism to account for the potent allergenicity of these common dust mite allergens.

T and B cell responses to HDM allergens and antigens

House dust mites provide well-characterized proteins to study human responses to inhaled antigens. Even in the absence of allergy they induce a high frequency of T cell precursors. The healthy response manifests by T cell proliferation and Th1 cytokines with little antibody. Responses of allergic people include Th1 and Th2 cytokines and IgE, IgG1, and IgG4 antibodies. Regulatory cells limit effector responses in healthy people. About half the IgE and IgG antibodies bind the group 1 and 2 allergens and 30% bind the group 4, 5, and 7 allergens. Although HLA independent, the recognition of the group 1 allergen shows an immunodominant region and a T cell receptor bias. The major allergens are not produced in higher amounts than many of the poorly non-allergenic proteins. The non-allergenic mite ferritin antigen shows high T cell proliferative responses with mixed cytokine production.

Application of Immunoreaction Enhancer Solutions to an Enzyme-Linked Immunosorbent Assay for Antigen-Specific IgE in Mice Immunized with Recombinant Major Mite Allergens or Ovalbumin

BACKGROUND

Weak signals for allergen-specific IgE are a problem in murine models for the study of allergies. It has been reported that the removal of IgG from murine sera enhances signal intensity. Very recently, buffer solutions designed to enhance signals in immunoassays have been developed and made commercially available.

METHODS

Sera from mice immunized either with a recombinant form of one of the major mite allergens Der p 1, Der f 1 and Der f 2, or with ovalbumin adsorbed to alum were used for the assays. Total IgE was measured by a sandwich enzyme-linked immunosorbent assay (ELISA). Allergen-specific IgE was assayed using plates coated with the allergens after the removal of IgG from sera with protein G-coupled sepharose beads in wells of other plates or with the use of commercially available enhancer solutions without the removal of IgG. IgE binding was detected with horseradish peroxidase-conjugated anti-murine IgE monoclonal antibody as the secondary antibody.

RESULTS

Significant levels of total IgE were produced after the immunizations. The in-well pretreatment of diluted sera (1/10 dilution) with protein G-coupled beads enhanced the signals for allergen-specific IgE. The use of the enhancer solutions for dilution of the sera and secondary antibody and prolonged incubation remarkably enhanced the signals at a more extensive dilution of sera (1/200 or less) without the removal of IgG.

CONCLUSIONS

An ELISA simply modified with the use of immunoreaction enhancer solutions has advantages in terms of signal intensity and ease of handling for the detection of allergen-specific murine IgE and would be useful for the study of allergies with murine models.

Crucial Commitment of Proteolytic Activity of a Purified Recombinant Major House Dust Mite Allergen Der p1 to Sensitization toward IgE and IgG Responses

The major proteolytic allergen derived from the house dust mite Dermatophagoides pteronyssinus, Der p1, is one of the most clinically relevant allergens worldwide. In the present study, we evaluate the contribution of the proteolytic activity and structure of a highly purified rDer p 1 to immune responses. Mice were i.p. immunized with three forms of rDer p 1 adsorbed to Alum: one enzymatically active, one treated with an irreversible cysteine protease-specific inhibitor, E-64, and one heat denatured. Immunization with E-64-treated or heat-denatured rDer p 1 elicited much less production of serum total IgE and not only rDer p 1-specific IgE but also IgGs compared with immunization with active rDer p 1. Assays for Ab-binding and its inhibition and structural analyses indicated that E-64-treated rDer p 1 retained its global structure and conformational B cell epitopes. A proliferative response and production of IL-5 by spleen cells restimulated with rDer p 1 were observed on immunization with the active rDer p 1 but not E-64-treated rDer p 1. The cells from mice immunized with heat-denatured rDer p 1 exhibited the highest levels of proliferation and production of IL-5 and IFN-gamma. The results indicate that the proteolytic activity of the highly purified rDer p 1 crucially commits to the sensitization process, including both IgE and IgG responses. Additionally, we demonstrated immunogenic differences by functional or structural manipulations of the rDer p 1. The findings have implications for sensitization to this relevant allergen in humans and for the design of modified allergen-vaccines for future allergen-specific immunotherapy.

Glycosylation of Recombinant Proforms of Major House Dust Mite Allergens Der p 1 and Der f 1 Decelerates the Speed of Maturation

BACKGROUND

The efficient manufacture of recombinant Der p 1 and Der f 1 has been an important bottleneck in the study of house dust mite allergies and the development of applications for allergen engineering. While Der f 1 has only one N-glycosylation motif in the mature sequence, Der p 1 has two motifs, one in the prosequence and the other in the mature sequence. To test whether inefficient maturation of a recombinant Pro-Der p 1 versus Pro-Der f 1 is due to N-glycosylation, the maturation speed of N-glycosylation motif mutants was compared.

METHODS

Expression vectors for the mutants, in which the motif in the Der p 1 prodomain was disrupted or a motif was created within the Der f 1 prodomain, were constructed by site-directed mutagenesis of preproforms with or without the motif within the mature portion. Culture supernatants of yeast Pichia pastoris transfectant cells containing proforms were buffer exchanged by gel filtration and incubated for maturation. Samples from the reactions were collected every 20 min and subjected to electrophoresis. The maturation speed was compared based on the band densities of the pro- and mature forms.

RESULTS

Disruption of the motif in the mature portion decreased the productivity and accelerated the maturation. Maturation was also accelerated by disruption of the other motif in the Der p 1 prodomain and slowed down by introduction of the motif into the Der f 1 prodomain.

CONCLUSIONS

Maturation systems using Pro-Der p 1 without the prodomain glycosylation are useful for the efficient preparation of a recombinant mature allergen. In addition, these results demonstrated that the maturation of cysteine protease could be controlled through glycosylation of the prodomain.

Molecular design of allergy vaccines

Recombinant-allergen-based diagnostic tests enable the dissection and monitoring of the molecular reactivity profiles of allergic patients, resulting in more specific diagnosis, disease monitoring, prevention and therapy. In vitro experiments, animal studies and clinical trials in patients demonstrate that allergenic molecules can be engineered to induce different immune responses ranging from tolerance to vigorous immunity. The available data thus suggest that molecular engineering of the disease-related antigens is a technology that may be applicable not only for the design of allergy vaccines but also for the design of vaccines against infectious diseases, autoimmunity and cancer.