Detection of novel latex allergens associated with clinically relevant allergy to plant-derived foods

Contact Allergy Induced by Mango (Mangifera indica): A Relevant Topic?

Introduction: The most common clinical manifestation of mango allergy is contact dermatitis, which can be localized or systemic. The sensitising substances that have long been suspected are alk(en)yl catechols and/or alk(en)yl resorcinols. Methods: We reviewed the original articles published on Pubmed, Embase and Cochrane Library before 15 September 2021, on the topic of contact allergy induced by mango and we synthesized the key data. Results: We found 12 case reports and four case series, with a total of 37 patients. Only seven of these cases were reported in patients from mango-cultivating countries, the other 30 were from countries where mango cultivation does not occur, and 26 were also from countries where poison ivy/oak are commonly found. We found that contact dermatitis may occur on the first exposure to mango due to previous sensitisation to urushiol-containing plants. The diagnosis was confirmed by patch testing in some of the cases. There was great heterogeneity between the reagents used. Conclusion: Mango fruit is frequently consumed, but mango induced contact dermatitis, the main hypersensitivity reaction induced by mango, is rare. Further data is necessary for a better understanding of sensitising substances and, consecutively, standardization of patch test reagents.

ENEA, a peach and apricot IgE-binding protein cross-reacting with the latex major allergen Hev b 5

Peach and apricot can cause allergic reactions with symptoms ranging from mild to very severe, including anaphylaxis. Sometimes subjects allergic to fruits of the Prunus genus have been reported to be also allergic to rubber latex products. The objective of this study is the characterization of a newly identified peach and apricot protein showing similarities with the allergens Hev b 5 from rubber latex and Man e 5 from manioc. This protein has been named ENEA on the basis of the single letter amino acid code of the first four N-terminal residues of the isolated molecule. It has been found in very variable amounts in different peach cultivars and batches. ENEA was isolated from peach pulp extracts by chromatographic separations and identified by direct protein sequencing. At that time, the full length sequence was available only for the homologous protein of the taxonomically closely related apricot, which was produced as a recombinant molecule in Escherichia coli. The following availability of the full length sequence of peach ENEA revealed a very high identity (97%) with the apricot homolog. Similarly to Hev b 5 and to Man e 5, the structural characterization indicated that ENEA is an intrinsically disordered protein. The immunological properties, investigated by dot blotting, the ABA system and the FABER test, showed that ENEA is recognized by specific IgE of allergic patients. In a selected population of 31 patients reporting allergic reactions to peach fruit and/or IgE positive to Hev b 5, 28 and 27 subjects resulted co-sensitized to rENEA and Hev b 5 in the ABA and ISAC test, respectively. In a random population of 3305 suspected allergic patients, analyzed with the FABER test, 17 of them were sensitized to rENEA and 10 of them were also positive to Hev b 5. In addition, both the natural molecule from peach and the recombinant protein of apricot partially inhibited the IgE binding to Hev b 5. In conclusion, a new peach and apricot IgE-binding protein, cross-reacting with the major latex allergen Hev b 5, has been identified. Its variable concentration in the fruit might explain some occasionally occurring allergic reactions. The apricot molecule has recently been registered by the WHO/IUIS Allergen Nomenclature Sub-Committee with the allergen name Pru ar 5. The recombinant form of apricot ENEA, now available, will contribute to allergy diagnosis.

Crystallization and identification of the glycosylated moieties of two isoforms of the main allergen Hev b 2 and preliminary X-ray analysis of two polymorphs of isoform II

Latex from Hevea brasiliensis contains several allergenic proteins that are involved in type I allergy. One of them is Hev b 2, which is a beta-1,3-glucanase enzyme that exists in different isoforms with variable glycosylation content. Two glucanase isoforms were isolated from trees of the GV-42 clone by gel filtration, affinity and ion-exchange chromatography. Isoform I had a carbohydrate content of about 20%, with N-linked N-acetyl-glucosamine, N-acetyl-galactosamine, fucose and galactose residues as the main sugars, while isoform II showed 6% carbohydrate content consisting of N-acetyl-glucosamine, fucose, mannose and xylose. Both isoforms were crystallized by the hanging-drop vapour-diffusion method. Isoform I crystals were grown using 0.2 M trisodium citrate dihydrate, 0.1 M Na HEPES pH 7.5 and 20%(v/v) 2-propanol, but these crystals were not appropriate for data collection. Isoform II crystals were obtained under two conditions and X-ray diffraction data were collected from both. In the first condition (0.2 M trisodium citrate, 0.1 M sodium cacodylate pH 6.5, 30% 2-propanol), crystals belonging to the tetragonal space group P4(1) with unit-cell parameters a = b = 150.17, c = 77.41 A were obtained. In the second condition [0.2 M ammonium acetate, 0.1 M trisodium citrate dihydrate pH 5.6, 30%(w/v) polyethylene glycol 4000] the isoform II crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a = 85.08, b = 89.67, c = 101.80 A, beta = 113.6 degrees. Preliminary analysis suggests that there are four molecules of isoform II in both asymmetric units.

Component-resolved diagnostics in food allergy

PURPOSE OF REVIEW

The purpose of this paper is to review and discuss recent studies on component-resolved diagnostics in food allergy, involving panels of pure allergen molecules or arrays of peptides derived from allergen sequences, and to summarize the reporting of new food allergens during the past 2 years.

RECENT FINDINGS

Several component-resolved diagnostic studies in food allergy suggest that the use of panels of allergen molecules may allow refined clinical information to be obtained on the likelihood or severity of an allergic food reaction and regarding diagnostic specificity. Further, in some studies the use of pure allergen molecules has led to a clearly higher sensitivity of the immunoglobulin E immunoassay compared with conventional allergen extracts.

SUMMARY

While common diagnostic methods in allergy assess the presence or absence of allergen-specific sensitization, to date, no in-vitro or in-vivo test exists which exhibits full correlation with clinical food allergy. A multitude of recently reported findings and observations indicate that molecular analysis of allergen sensitization pattern may serve to enhance the clinical utility of immunoglobulin E antibody-based allergy diagnostics. Pure natural and recombinant allergen molecules as well as panels of synthetic peptides have been used for this purpose.