2S protein Ara h 7.0201 has unique epitopes compared to other Ara h 7 isoforms and is comparable to 2S proteins Ara h 2 and 6 in basophil degranulation capacity

Abstract

Summary Background Screening for specific IgE against 2S albumin proteins Ara h 2 and 6 has good positive predictive value in diagnosing peanut allergy. From the third 2S member Ara h 7, 3 isoforms have been identified. Their allergenicity has not been elucidated. Objective This study investigated the allergenicity of Ara h 7 isoforms compared to Ara h 2 and 6. Methods Sensitization of 15 DBPCFC‐confirmed peanut‐allergic patients to recombinant Ara h 2.0201, Ara h 6.01 and isoforms of recombinant Ara h 7 was determined by IgE immunoblotting strips. A basophil activation test (BAT) was performed in 9 patients to determine IgE‐cross‐linking capacities of the allergens. Sensitivity to the allergens was tested in 5 patients who were sensitized to at least 1 Ara h 7 isoform, by a concentration range in the BAT. 3D prediction models and sequence alignments were used to visualize differences between isoforms and to predict allergenic epitope regions. Results Sensitization to Ara h 7.0201 was most frequent (80%) and showed to be equally potent as Ara h 2.0201 and 6.01 in inducing basophil degranulation. Sensitization to Ara h 7.0201 together with Ara h 2.0201 and/or 6.01 was observed, indicating the presence of unique epitopes compared to the other 2 isoforms. Differences between the 3 Ara h 7 isoforms were observed in C‐terminal cysteine residues, pepsin and trypsin cleavage sites and 3 single amino acid substitutions. Conclusion & clinical relevance The majority of peanut‐allergic patients are sensitized to isoform Ara h 7.0201, which is functionally as active as Ara h 2.0201 and 6.01. Unique epitopes are most likely located in the C‐terminus or an allergenic loop region which is a known allergenic epitope region for Ara h 2.0201 and 6.01. Due to its unique epitopes and allergenicity, it is an interesting candidate to improve the diagnostic accuracy for peanut allergy.

Ara h 7 isoforms share many linear epitopes: Are 3D epitopes crucial to elucidate divergent abilities?

“…Divergent abilities of Ara h 7 isoforms in inducing basophil degranulation suggested the presence of unique epitopes for Ara h 7.0201 as compared to the other isoforms. This hypothesis was supported by inhibition assays showing complete inhibition of IgE‐binding to Ara h 7.0101 by Ara h 7.0201, although IgE‐binding to Ara h 7.0201 was not fully inhibited by Ara h 7.0101 . These observations can partially be elucidated by the newly mapped linear epitopes in this study.…”

“…In a previous study, the ability to induce basophil degranulation was studied for all Ara h 7 isoforms . Patients D‐23, V‐01, and D‐13 correspond to the patients N07, N12, and N14, respectively, in that study.…”

“…For diagnosing peanut allergy, IgE antibodies against Ara h 2 and Ara h 6 are known to have a very high positive predictive value . Recently, IgE‐binding to Ara h 7 showed a discriminative ability comparable to Ara h 2 and Ara h 6 and this 2S albumin was as potent as Ara h 2 and h 6 in inducing basophil degranulation . For Ara h 7, three different isoforms—Ara h 7.0101, Ara h 7.0201, Ara h 7.0301—have been described whilst Ara h 7.0101 has only be detected on cDNA but not on protein level .…”

“…This data suggest the presence of unique epitopes on Ara h 7.0201 . By amino acid sequence comparisons, these unique epitopes might be located on the distinctive C‐terminus or created by amino acid substitutions within the flexible loops that are sensitive to pepsin or trypsin . The aim of the study was to define linear epitopes of Ara h 7 isoforms.…”

A new approach to oral allergen immunotherapy for food allergy?

“…Also in this issue of the Journal, Hayen et al have looked at the allergenicity of the new 2S Ara h 7 isoforms compared to the Ara h 2 and 6 2S allergens. They utilised serum from 15 individuals with double‐blind, placebo‐controlled food challenge defined peanut allergy.…”