IgE-binding to vicilin-like antimicrobial peptides is associated with systemic reactions to macadamia nut

Thuy-My Le,Henny G Otten,Waltraud Suer,Stefanie Rohwer,André C Knulst,Anna M Ehlers,Bettina Brix

doi:10.1186/s13601-020-00364-5

Abstract

BackgroundMacadamia nut can induce fatal allergic reactions and changes in dietary habits will raise their consumption in industrialised countries. Until now diagnosis of macadamia nut allergy by sIgE solely relies on the macadamia nut extract, but single components are lacking.MethodsMacadamia nut proteins recognised by IgE from 2 macadamia nut extract positive sera were identified by mass spectrometry (vicilin-like antimicrobial peptides: VLAP). Sensitisation to macadamia nut extract and heterologously expressed isoform VLAP-2–3 was evaluated in 82 nut allergic (NA) and 27 tolerant (NT) patients (no tree nut allergy reported) comprehending 10 macadamia nut allergic (MA) and 18 explicitly reported macadamia nut tolerant patients (MT), using line blots. Co-sensitisation to additional VLAP isoforms and other vicilins was evaluated in 8 MA, 12 MT and 14 NA patients sensitised to VLAP-2–3. Functional properties were determined by indirect basophil activation.ResultsEven though proteins recognised by IgE were identified as VLAP-2–1, 2–2 and 2–3, only peptides specifically belonging to VLAP-2–3 were detected by mass spectrometry. The macadamia nut extract was recognised by 33% of NA patients (27/82) including 3 MA patients and 26% of NT patients (7/27, 3 MT). Similarly, 29% of NA (24/82) patients showed partly strong sIgE-binding to VLAP-2–3 including 3 MA patients with systemic reactions to macadamia nut. Contrary, VLAP-2–3 was recognised by only 2 NT (1 MT) patients (7%) with very low sIgE titres. Simultaneous recognition of the isoforms VLAP-2–1 and 2–2 was observed in all patients positive for VLAP-2–3 with partly reduced sIgE titres in 59% of these patients. Additionally, all three VLAP isoforms were able to repeatedly induce BAT reactivity upon sensitisation with a MA serum.ConclusionVLAP proteins are the first described macadamia nut components with serological and functional allergenic properties and they are associated with systemic reactions to macadamia nut.

Highlights

Macadamia nut can induce fatal allergic reactions and changes in dietary habits will raise their con‐ sumption in industrialised countries
Even though macadamia nut is currently responsible for a small number of tree nut allergic reactions [3], it is hypothesized that the number will raise due to changes in dietary habits and increasing use in pastry and confectionery [4]
We identified vicilinlike antimicrobial peptides (VLAP) 2–1, 2–2 and 2–3 as novel allergens

Summary

Introduction

Macadamia nut can induce fatal allergic reactions and changes in dietary habits will raise their con‐ sumption in industrialised countries. Binding to vicilins from other tree nuts, legumes and seeds was analysed in a subgroup of 8 MA, 12 macadamia nut tolerant (MT) and 14 NA patients sensitised to VLAP-2–3. Proteins with a molecular mass between 53 and 67 kDa and an isoelectric point (pI) between 6.3 and 8.7 were strongly bound by sIgE from 2 macadamia nut sensitised sera (Additional file 3: Figure S1; Serum 1: 18 RU VLAP-2–3 [a], Serum 2: 114 RU VLAP-2–3 [b]).

Results

Conclusion