A single amino acid substitution on the surface of a natural hevein isoform (Hev b 6.0202), confers different IgE recognition

Hevein-Like Antimicrobial Peptides of Plants

Plant antimicrobial peptides represent one of the evolutionarily oldest innate immunity components providing the first line of host defense to pathogen attacks. This review is dedicated to a small, currently actively studied family of hevein-like peptides that can be found in various monocot and dicot plants. The review thoroughly describes all known peptides belonging to this family including data on their structures, functions, and antimicrobial activity. The main features allowing to assign these peptides to a separate family are given, and the specific characteristics of each peptide are described. Further, the mode of action for hevein-like peptides, their role in plant immune system, and the applications of these molecules in biotechnology and medicine are considered.

Optimization of allergen standardization

Preparation of high quality allergen extracts is essential for the diagnosis and immunotherapy of allergic disorders. Standardization of allergen extracts concerns determination of the allergen unit, development of reference material and measurement of the overall IgE binding capacity of an allergen extract. Recently, quantification of individual allergens has been the main focus of allergen standardization because the allergenicity of most allergen extracts is known to be mainly dependent on the content of a small number of allergen molecules. Therefore, characterization of major allergens will facilitate the standardization of allergens. In this article, we review the current state of allergen standardization. In addition, we briefly summarize the components of allergen extracts that should be under control for the optimization of allergen standardization, since its adjuvant-like activities could play an important role in allergic reactions even though the molecule itself does not bind to the IgE antibodies from subjects.

Latex-allergic patients sensitized to the major allergen hevein and hevein-like domains of class I chitinases show no increased frequency of latex-associated plant food allergy

Allergies to certain fruits such as banana, avocado, chestnut and kiwi are described in 30–70% of latex-allergic patients. This association is attributed to the cross-reactivity between the major latex allergen hevein and hevein-like domains (HLDs) from fruit class I chitinases. We aimed to assess the extent of cross-reactivity between hevein and HLDs using sera from latex-allergic patients with and without plant food allergy. Hevein and HLDs of latex, banana, and avocado chitinases were expressed in Escherichia coli as fusion proteins with the maltose-binding protein and purified by affinity chromatography. IgE binding to these proteins was studied in sera from 59 latex-allergic patients and 20 banana-allergic patients without latex allergy by ELISA and ELISA inhibition. Additionally, 16,408 allergic patients’ sera were tested for IgE binding to hevein, latex chitinase, and wheat germ agglutinin using an allergen microarray. Hevein-specific IgE was detected in 34/59 (58%) latex-allergic patients’ sera. HLDs of latex, banana, and avocado chitinases were recognized by 21 (36%), 20 (34%), and 9 (15%) sera, respectively. In contrast, only one of 20 banana-allergic patients without latex allergy was sensitized to chitinase HLDs. In most tested latex-allergic patients’ sera, IgE binding to hevein was only partially reduced by preincubation with HLDs. Among hevein-sensitized, latex-allergic patients, the percentage of plant food allergy (15/34 = 44%) was equal to latex-allergic patients without hevein sensitization (11/25 = 44%). In the general allergic population, 230 of 16,408 sera (1.4%) reacted to hevein and/or a hevein-like allergen. Of these, 128 sera showed an isolated sensitization to hevein, whereas only 17 bound to latex chitinase or wheat germ agglutinin without hevein sensitization. In conclusion, the IgE response to HLDs is elicited by hevein as sensitizing allergen in most cases. Despite considerable cross-reactivity between these allergens, no correlation between latex-associated plant food allergy and sensitization to hevein or HLDs was found.

Analysis of B-cell epitopes from the allergen Hev b 6.02 revealed by using blocking antibodies

Hev b 6.02 (hevein), identified as a major allergen from natural rubber latex (NRL), is involved in the latex-fruit syndrome and also acts as a pathogenesis defense-related protein. Its 3D structure has been solved at high resolution, and its linear epitopes have already been reported. However, information about conformational epitopes is still controversial, even though it is relevant for an accurate diagnosis and treatment, as well as for the study of allergen-antibody molecular interactions. We sought to analyze the B-cell epitopes of Hev b 6.02 at a molecular and structural level, using specific recombinant antibodies. We obtained a murine monoclonal antibody (mAb 6E7) and three human single chain fragments (scFvs A6, H8, and G7) anti-Hev b 6.02 that were able to compete for hevein binding with serum IgEs from latex allergic patients. In vitro assays showed that the mAb 6E7 and scFv H8 recognized the area of Hev b 6.02 where the aromatic residues are exposed; while the scFv G7 defined the amino and carboxy-terminal regions that lie close to each other, as a different epitope. The structural modeling of the Hev b 6.02-scFv H8 and Hev b 6.02-scFv G7 complexes revealed the putative regions of two conformational epitopes. In one of these, the aromatic residues, as well as polar side chains are important for the interaction, suggesting that they are part of a dominant conformational epitope also presented on the Hev b 6.02-IgE interactions. Antibodies recognizing this important allergen have potential to be used to diagnose and ultimately treat latex allergy.

Sequence polymorphisms of major German cockroach allergens Bla g 1, Bla g 2, Bla g 4, and Bla g 5

BACKGROUND

The allergenicity of allergens could be influenced by amino acid substitutions in B- or T-cell epitope regions. The German cockroach is known to produce potent allergens inducing strong IgE-mediated allergic reactions. This study was performed to investigate sequence variations in major allergens of the German cockroach.

METHODS

Reverse transcriptase PCR was used to amplify the cDNA sequences encoding major allergens of the German cockroach (Bla g 1, Bla g 2, Bla g 4, and Bla g 5).

RESULTS

The deduced amino acid sequences revealed 38 Bla g 1 variants with 1-7 amino acid substitutions (98.6-99.8% identity), 28 Bla g 2 variants with 1-3 substitutions (99.1-99.7%), 27 Bla g 4 variants with 0-32 substitutions (82.4-100%), and 8 Bla g 5 variants with 1-2 substitutions (99.0-99.5%), respectively. Bla g 1 and Bla g 2 showed sporadic amino acid substitutions despite the divergence in their sequences. Bla g 4 exhibited frequent variations, with clusters of substitutions in residues 29-38, 52-80, and 132-155. Sequence variations in Bla g 4 imply the presence of multiple isoforms and isoallergens, which may in turn have various effects on the IgE-binding capacity and T-cell responsiveness. Only 8 variants were found in Bla g 5, with infrequent amino acid changes of one or two residues.

CONCLUSIONS

Analyses of T-cell and IgE-binding epitope regions would clarify the effect of sequence polymorphisms on allergenicity, which in turn will aid in the design of allergen formulations for diagnosis and immunotherapy for cockroach allergies.