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

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, three 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, 6.01 and isoforms of recombinant Ara h 7 was determined by IgE immunoblotting strips. A basophil activation test (BAT) was performed in nine patients to determine IgE-crosslinking capacities of the allergens. Sensitivity to the allergens was tested in five patients that were sensitized to at least one 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 two isoforms. Differences between the three Ara h 7 isoforms were observed in C-terminal cysteine residues, pepsin and trypsin cleavage sites and three 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.

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