Profiling the Extended Cleavage Specificity of the House Dust Mite Protease Allergens Der p 1, Der p 3 and Der p 6 for the Prediction of New Cell Surface Protein Substrates

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

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

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.

House dust mite-derived allergens effect on matrix metalloproteases in airway epithelial cells

Aim of the Study: Many allergens have protease activities. Although the immunomodulatory effects of these antigens are well known, the effects attributed to their protease activities are not thoroughly investigated. We set out to determine the effects of house dust mite (HDM) allergens with varying protease activities on bronchial epithelial cell functions. Materials and methods: BEAS-2B cells were maintained in ALI-culture and stimulated with Der p1 (cysteine protease), Der p6 (serine protease), and Der p2 (non-protease) with and without specific protease inhibitors or heat denaturation. Cell viability and epithelial permeability were measured with MTT and paracellular flux assay, respectively. The effect of heat denaturation on allergen structure was examined using in silico models. Matrix metalloproteinases (MMPs) were investigated at the transcription (qPCR), protein (ELISA), and functional (zymography) levels. Results: Epithelial permeability increased only after Der p6 but not after Der p1 or Der p2 stimulation. Der p2 increased both MMP-2 and MMP-9 expression, while Der p1 increased only MMP-9 expression. The heat-denatured form of Der p1 unexpectedly increased MMP-9 gene expression, which, through the use of in silico models, was attributed to its ability to change receptor connections by the formation of new electrostatic and hydrogen bonds. IL-8 and GM-CSF production were increased after Der p1 and Der p2 but decreased after Der p6 stimulation. IL-6 decreased after Der p1 but increased following stimulation with Der p6 and heat-denatured Der p2. Conclusion: Allergens in house dust mites are capable of inducing various changes in the epithelial cell functions by virtue of their protease activities.

House Dust Mite Allergy and the Der p1 Conundrum: A Literature Review and Case Series

The house dust mite (HDM) is globally ubiquitous in human habitats. Thirty-two allergens for Dermatophagoides farinae and 21 for Dermatophagoides pteronyssinus have been detected so far. The present minireview summarizes information about the role of Der p 1 as a key coordinator of the HDM-induced allergic response and reports on a series of Italian patients who are allergic to HDMs. We studied the specific IgE profiles in a population of patients with allergic asthma and rhinitis screened for specific immunotherapy (SIT) for HDM allergies, with the aim of obtaining insights into the pathogenic role of Der p1. Patients co-sensitized to other airborne allergens showed a higher prevalence of asthma (9/12 (75%) vs. 2/7 (29%); p < 0.05) than did HDM mono-sensitized patients. The latter group showed higher Der p1 concentrations than that of the co-sensitized group (p = 0.0360), and a direct correlation between Der p1 and Der p2 (r = 0.93; p = 0.0003) was observed. In conclusion, our study offers insights into the role of Der p1 in a population of patients with allergic rhinitis and asthma who were candidates for SIT. Interestingly, Der p1 positivity was associated with bronchial asthma and co-sensitization.

Dermatophagoides spp. hypoallergens design: what has been achieved so far?

Introduction: Allergic illnesses are one of the most prevalent immunological disorders worldwide and house dust mites are important triggers of these diseases. Allergen-specific immunotherapy (AIT) is an alternative treatment to pharmacotherapy and among its technologies, recombinant hypoallergenic derivatives have shown promising features, turn them into safer and more efficient allergy vaccines.Areas covered: Patents and scientific publications referring to advances in the design of Dermatophagoides spp. hypoallergenic molecules. Data were obtained from the Espacenet® and PubMed websites, using different key terms, advanced tools and Boolean operators for searches. The retrieved data were then descriptively analyzed, taking into consideration clinical targets, geographical, temporal, collaborative, and different classification aspects of the productions.Expert opinion: Joint advances of molecular biology, genetic engineering, and bioinformatics technologies led to progresses in the design of Dermatophagoides spp. hypoallergenic derivatives. Collaborative networks seem to be an interesting way not only to improve technologies in AIT but also to boost the number of patents, publications, and grants for researchers. The observed trend for the use of hypoallergenic hybrid molecules was a fundamental AIT advance and this type of molecule appears to be a more attractive product for companies and more convenient, efficient, and safer allergy immunotherapy for patients.

Surface loops of trypsin-like serine proteases as determinants of function

Trypsin and chymotrypsin-like serine proteases from family S1 (clan PA) constitute the largest protease group in humans and more generally in vertebrates. The prototypes chymotrypsin, trypsin and elastase represent simple digestive proteases in the gut, where they cleave nearly any protein. Multidomain trypsin-like proteases are key players in the tightly controlled blood coagulation and complement systems, as well as related proteases that are secreted from diverse immune cells. Some serine proteases are expressed in nearly all tissues and fluids of the human body, such as the human kallikreins and kallikrein-related peptidases with specialization for often unique substrates and accurate timing of activity. HtrA and membrane-anchored serine proteases fulfill important physiological tasks with emerging roles in cancer. The high diversity of all family members, which share the tandem β-barrel architecture of the chymotrypsin-fold in the catalytic domain, is conferred by the large differences of eight surface loops, surrounding the active site. The length of these loops alters with insertions and deletions, resulting in remarkably different three-dimensional arrangements. In addition, metal binding sites for Na+, Ca2+ and Zn2+ serve as regulatory elements, as do N-glycosylation sites. Depending on the individual tasks of the protease, the surface loops determine substrate specificity, control the turnover and allow regulation of activation, activity and degradation by other proteins, which are often serine proteases themselves. Most intriguingly, in some serine proteases, the surface loops interact as allosteric network, partially tuned by protein co-factors. Knowledge of these subtle and complicated molecular motions may allow nowadays for new and specific pharmaceutical or medical approaches.

Alpha 1 antitrypsin distribution in an allergic asthmatic population sensitized to house dust mites

Background and objective

Severe alpha1 antitrypsin deficiency has been clearly associated with pulmonary emphysema, but its relationship with bronchial asthma remains controversial. Some deficient alpha 1 antitrypsin (AAT) genotypes seem to be associated with asthma development. The objective of this study was to analyze the distribution of AAT genotypes in asthmatic patients allergic to house dust mites (HDM), and to asses a possible association between these genotypes and severe asthma.

Methods

A cross-sectional cohort study of 648 patients with HDM allergic asthma was carried out. Demographic, clinical and analytical variables were collected. PI*S and PI*Z AAT deficient alleles of the SERPINA1 gene were assayed by real-time PCR.

Results

Asthma was intermittent in 253 patients and persistent in 395 patients (246 mild, 101 moderate and 48 severe). One hundred and forty-five asthmatic patients (22.4%) with at least one mutated allele (S or Z) were identified. No association between the different genotypes and asthma severity was found. No significant differences in all clinical and functional tests, as well as nasal eosinophils, IgA and IgE serum levels were observed. Peripheral eosinophils were significantly lower in patients with the PI*MS genotype (p = 0.0228). Neither association between deficient AAT genotypes or serum ATT deficiency (AATD) and development of severe asthma, or correlation between ATT levels and FEV1 was observed.

Conclusion

In conclusion, the distribution of AAT genotypes in HDM allergic asthmatic patients did not differ from those found in Spanish population. Neither severe ATTD or deficient AAT genotypes appear to confer different clinical expression of asthma.

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.