Seed storage 2S albumins are predictive indicators of exclusive Anacardiaceae cross‐reactivity

Abstract

wileyonlinelibrary.com/journal/cea | 545 © 2019 John Wiley & Sons Ltd Pistachio (Pistachio vera) and cashew nut (Anacardium occidentale), members of the Anacardiaceae family, account for a significant percentage of food allergies worldwide.1 Nuts are one of the main causes of food anaphylaxis, eliciting a significant number of lifethreatening reactions, which are aggravated by the fact that these allergens are often hidden in processed foods. Variability of allergic phenotypes to nut allergens with complex crossreactivity profiles complicates clinical management of the patient.2 In this sense, several allergenic patterns have been defined according to different factors such as geographical area, age, eating habits, pollinosis, and so on. Most nut allergens belong to a small number of protein families, which homologous members share threedimensional structure, biologic function and sequence identity, exhibiting inter and intraspecies crossreactivity. In a clinic context, it is important to establish correlations within each food allergen family based on their crossreactivity and their ability to trigger systemic reactions or anaphylaxis. Nowadays, the availability of few purified and wellcharacterized allergens makes difficult to predict which of them are included in these particular associations. Different nuts clusters, grouped around one allergen, make it possible to optimize the management of nut allergy. Previous studies have shown that pistachio and cashew nut presented a high degree of crossreactivity at the specific IgE (sIgE) level, owing to their botanic proximity.3 Furthermore, at least 86% of patients allergic to nuts are also allergic to multiple species4 and for cashew or pistachio allergic subjects a significant proportion are polysensitized to different nuts. Several major allergens have been identified in cashew Ana o 1 (7S vicilin), Ana o 2 (11S globulin), Ana o 3 (2S albumin),5 and in pistachio Pis v 1 (2S albumin), Pis v 2 and 5 (11S globulin), Pis v 3 (7S globulin) and Pis v 4.6 Except Pis v 4, a manganese superoxide dismutase, all others are seed storage proteins. Prior studies showed that 7S vicilins and 11S globulins from different tree nuts exhibit moderate crossreactivity at IgE level.7 However, crossreactivity mediated by 2S albumins has not been well explored and appears to be infrequent and, as in Brassicaceae seeds, nearly restricted to members of phylogenetically related families.8 The aim of the present study was to evaluate a selected group of six patients with allergy to pistachio and/or cashew nut exclusively sensitized to 2S albumins. Results of this study proved that there is IgE crossreactivity between these two Anacardiaceae 2S albumins but they were not crossreactive to 2S albumins from other sources, which will provide significant data on the clinical management of this subgroup of patients. These patients displayed clinical features described in Table 1. All the patients reported systemic symptoms when eating pistachio and/or cashew nut and showed positive skin test to these nut extracts and sIgE to their 2S albumins, Pis v 1 and Ana o 3, respectively. None of them was sensitized to other nuts or purified 2S albumins (skin test or specific IgE), or allergic to other nuts, which was confirmed by oral challenge test. ImmunoCAP revealed that all patients, with the exception of one patient who have sIgE < 0.1 kU/L against pistachio, were positive to both nuts, pistachio and cashew. Sensitization to pistachio in this patient was confirmed by ELISA and immunoblotting. Controls did not show any positive result. IgEbinding assays showed similar protein pattern recognition to cashew nut and pistachio extracts (Figure 1A). Five out of the six patients (83%) with systemic reactions recognized bands around 14kDa in both pistachio and cashew nut extracts. IgEreactive proteins were separated by using a combination of size exclusion chromatography Received: 2 October 2018 | Revised: 19 December 2018 | Accepted: 9 January 2019 DOI: 10.1111/cea.13357