Identification of immunodominant IgE binding epitopes of Der p 24, a major allergen of Dermatophagoides pteronyssinus

Immunobiological properties and structure analysis of group 13 allergen from Blomia tropicalis and its IgE-mediated cross-reactivity

Blomia tropicalis is an important species of allergenic mite. Structurally related cross-reactive allergens are involved in pathogenesis of clinical symptoms. The present study focused on recombinant allergen rBlo t 13 from B. tropicalis, including investigation of its structure, immunological properties, IgE-mediated cross-reactivity. In this work, the prokaryotic expression plasmids pET-28(a)-Blo t 13, pET-28(a)-Der f 13, and pET-28(a)-Tyr p 13 were constructed, transformed into E. coli Rosetta (DE3) pLysS, and purified by nickel affinity chromatography, respectively. By using ELISA, the IgE-binding rates were detected for rBlo t 13 and its epitope peptides, as well as the cross-reactivity among rBlo t 13, rDer f 13, and rTyr p 13. The tertiary structure of rBlo t 13 was resolved using X-ray diffraction at 2.0 Å resolution. Using IgE-ELISA, the IgE binding rate of rBlo t 13 was 60 % with Blomia tropicalis-positive sera. In the experiments of ELISA for cross-reactivity with rBlo t 13 on solid phase, the inhibition rates were 65 %, 57 % and 63 % for rBlo t 13, rDer f 13, and rTyr p 13, respectively. The structure of Blo t 13 protein contains a β-barrel structure which is composed of 10 β strands and has 2 α helices at the end of the barrel. Comparison of the tertiary structures of rBlo t 13, rDer f 13, and rTyr p 13 revealed that the β-barrel structure is highly conserved, consistent with the alignment of amino acid sequences. We obtained the recombinant protein rBlo t 13, demonstrated its cross-reactivity with Der f 13 and Tyr p 13 due to their structural similarity.

Identification of an immunodominant IgE epitope of Der f 40, a novel allergen of Dermatophagoides farinae

Background

House dust mites (HDMs), including Dermatophagoides pteronyssinus (Der p) and Dermatophagoides farinae (Der f) species, represent a major source of inhalant allergens that induce IgE-mediated anaphylactic reactions. HDM allergen identification is important to the diagnosis and treatment of allergic diseases. Here, we report the identification of a novel HDM allergen, which we suggest naming Der f 40, and its immunodominant IgE epitopes.

Methods

The recombinant protein Der f 40 was expressed using a pET prokaryotic expression system and purified with Ni-NTA resins. IgE binding activity was evaluated by IgE-western blot, dot-blot, and ELISA. Mast cell activation testing was performed to assess the cellular effects of IgE binding in mouse bone marrow derived mast cells (BMMCs) expressing human FcεRI. IgE binding assays were performed with truncated and hybrid Der f 40 protein molecules to find immunodominant IgE epitopes.

Results

A 106-amino acid (aa) recombinant Der f Group 40 protein (rDer f 40) was obtained (GenBank accession No. XP_046915420.1) as thiredoxin-like protein. Der f 40 was shown to bind IgE from HDM allergic serum in vitro (9.68%; 12/124 in IgE-ELISA), and shown to promote the release of β-hexosaminidase from BMMCs dose-dependently when administered with HDM allergic sera. The Der f Group 40 protein was named Der f 40 and listed in the World Health Organization and International Union of Immunological Societies (WHO/IUIS) Allergen Nomenclature Sub-committee. IgE binding assays with Der f 40-based truncated and hybrid proteins indicated that IgE binding epitopes are likely located in the C-terminal region and dependent on conformational structure. The 76-106-aa region of C-terminus was identified as an immunodominant IgE epitope of Der f 40.

Conclusion

A novel HDM allergen with robust IgE binding activity was identified and named Der f 40. An immunodominant IgE epitope of Der f 40 with conformational dependency was identified in the C-terminus (aa 76-106). These findings provide new information that may be useful in the development of diagnostic and therapeutic agents for HDM allergy.

Designing an epitope vaccine against Dermatophagoides pteronyssinus: An in silico study

The house dust mite, Dermatophagoides pteronyssinus, is a major source of the inhaled allergen Der p 1, which causes immunoglobulin E (IgE)-mediated hypersensitivity reactions manifesting in allergic diseases. To date, no drugs or vaccines effectively treat or prevent Der p 1 sensitization. We applied in silico immunoinformatics to design T-cell and B-cell epitopes that were specified and developed from the allergen Der p 1 of D. pteronyssinus. We identified the conserved epitope areas by predicting the accessibility and flexibility of B-cell epitopes, and the percentage of human leukocyte antigen representing T cells. Molecular docking using HADDOCK software indicated three optimal clusters: cluster 6 (z-score: -2.1), cluster 1 (z-score: -1.2), and cluster 3 (z-score: -0.6). The most negative Z-score was found in cluster 6, which represented three epitopes. The interaction between A chain proteins (IgE protein residues) and B chains (Der p 1 protein residues) exhibited a knowledge-based FADE and contact value >1, suggesting the best protein interactions occurred in the conserved area. Molecular dynamic simulation further predicted the stable nature of Der p 1 protein. The IQRDNGYQP region is the best candidate to be utilized as a D. pteronyssinus epitope vaccine, which could be used in the development of allergen-specific immunotherapy.

Enolase-specific cross antibodies induce neutrophilic inflammation in the intestine

The pathogenesis of ulcerative colitis (UC) is to be further investigated. House dust mites (HDM) are highly associated with the pathogenesis of immune inflammation in the body. This study aims to investigate the role of enolase (one of the HDM-derived proteins)-specific cross Abs in the induction of UC-like inflammation. The enolase specific IgG (EsIgG) was identified in UC patients by mass spectrometry. Mice were treated with EsIgG to induce inflammation in the colon mucosa. EsIgG was detected in the serum and the colon tissues of UC patients, which was positively correlated with the polymorphonuclear neutrophil (PMN) counts in the blood and colon tissues of UC patients. EsIgG formed immune complexes with the constitutive enolase in the UC colon epithelium that activated complement, induced epithelial cell apoptosis, compromised epithelial barrier functions, and resulted in UC-like inflammation in the mouse colon. In summary, UC patients have high serum levels of Abs against HDM-derived enolase and intestinal epithelial cell-derived enolase. These Abs attack the colonic epithelium to induce UC-like inflammation.

Highlights and recent developments in allergic diseases in EAACI journals (2019)

The European Academy of Allergy and Clinical Immunology (EAACI) owns three journals: Allergy, Pediatric Allergy and Immunology and Clinical and Translational Allergy. One of the major goals of EAACI is to support health promotion in which prevention of allergy and asthma plays a critical role and to disseminate the knowledge of allergy to all stakeholders including the EAACI junior members. There was substantial progress in 2019 in the identification of basic mechanisms of allergic and respiratory disease and the translation of these mechanisms into clinics. Better understanding of molecular and cellular mechanisms, efforts for the development of biomarkers for disease prediction, novel prevention and intervention studies, elucidation of mechanisms of multimorbidities, entrance of new drugs in the clinics as well as recently completed phase three clinical studies and publication of a large number of allergen immunotherapy studies and meta-analyses have been the highlights of the last year.

The allergenic activity and clinical impact of individual IgE-antibody binding molecules from indoor allergen sources

A large number of allergens have been discovered but we know little about their potential to induce inflammation (allergenic activity) and symptoms. Nowadays, the clinical importance of allergens is determined by the frequency and intensity of their IgE antibody binding (allergenicity). This is a rather limited parameter considering the development of experimental allergology in the last 20 years and the criteria that support personalized medicine. Now it is known that some allergens, in addition to their IgE antibody binding properties, can induce inflammation through non IgE mediated pathways, which can increase their allergenic activity. There are several ways to evaluate the allergenic activity, among them the provocation tests, the demonstration of non-IgE mediated pathways of inflammation, case control studies of IgE-binding frequencies, and animal models of respiratory allergy. In this review we have explored the current status of basic and clinical research on allergenic activity of indoor allergens and confirm that, for most of them, this important property has not been investigated. However, during recent years important advances have been made in the field, and we conclude that for at least the following, allergenic activity has been demonstrated: Der p 1, Der p 2, Der p 5 and Blo t 5 from HDMs; Per a 10 from P. americana; Asp f 1, Asp f 2, Asp f 3, Asp f 4 and Asp f 6 from A. fumigatus; Mala s 8 and Mala s 13 from M. sympodialis; Alt a 1 from A. alternata; Pen c 13 from P. chrysogenum; Fel d 1 from cats; Can f 1, Can f 2, Can f 3, Can f 4 and Can f 5 from dogs; Mus m 1 from mice and Bos d 2 from cows. Defining the allergenic activity of other indoor IgE antibody binding molecules is necessary for a precision-medicine-oriented management of allergic diseases.

Identification of immunodominant IgE epitopes of the major house dust mite allergen Der f 24

Previously, a ubiquinol-cytochrome c reductase binding protein (UQCRB) homolog was identified in the house dust mite (HDM) species Dermatophagoides farinae (Der f) as a major allergen. In the present study, the immunodominant immunoglobulin E (IgE) epitope of the protein Der f 24 was investigated. Analysis of the homologous amino acid (aa) sequences in Der f and human UQCRB was performed. Four different recombinant Der f 24 and hybrid proteins formed by integrating Der f and human UQCRB sequences were expressed in Escherichia coli, purified using Ni-NTA resins, and IgE-binding activity was determined using IgE-western blotting and enzyme-linked immunosorbent assay (ELISA) experiments. IgE epitopes were further identified by IgE-dot blotting and IgE-ELISA with synthetic polypeptides and HDM-allergic sera. Three-dimensional (3D) structural modeling was used to analyze the position of the immuno-dominant IgE epitope. The amino acid sequence homology between Der f 24 and the human UQCRB protein was determined to be 39.34%. IgE-ELISA and western blot analysis showed that all of the Der f-human UQCRB hybrid proteins generated, except for the one lacking 59 residues of the N-terminal region of Der f 24, were bound by allergic serum IgE. A synthetic polypeptide consisting of 32 residues of the N-terminal reacted with IgEs from HDM-allergic sera and could be used to generate high titer specific IgG or specific IgE antibodies in immunized mice. The 32-aa N-terminal region of Der f 24 was localized to a structural protrusion, which may facilitate specific IgE-binding. These results indicate that the immunodominant IgE epitope of Der f 24 is located mainly in a 32-residue region of the N-terminus. These findings may inform the mechanisms of HDM allergy sensitization and allergy immunotherapy development.