Peanut and tree nut allergies
After this module, participants will be able to:
- Identify and describe which components can be used in component-resolved diagnostics (CRD) to aid the diagnosis and management of peanut and tree nut allergies.
- Explain the different cross-reactions that can occur between peanuts, tree nuts and other allergen sources.
- Nuts are a major food in all diets worldwide. In Europe, they are primarily consumed in a roasted form, eaten whole, as nut butters or as ingredients in food products.1
- Peanuts are classified as legumes (as opposed to nuts) and respective allergies have been shown to affect 2% of children in the UK.2
- Allergies can also be induced by tree nuts, such as hazelnuts, cashew nuts and walnuts.3
- Generally, there are two types of nut allergy: 4
- Primary nut allergy – a systemic, often severe reaction to nuts in patients sensitised to major storage proteins
- Pollen food syndrome – a distinct disorder with generally mild oral/pharyngeal symptoms due to a pollen sensitisation, which can be triggered by nuts
- In northern and central European countries, reactions to hazelnut are often driven by birch pollen.5
- The allergenicity of nuts can be altered through processing. For example, roasting at high temperatures has been shown to increase the allergenicity of Ara h 1 (peanut) by inducing the formation of globular protein aggregates.6
Allergens in peanut, hazelnut and cashew nut1
PR, pathogenesis-related; nsLTP, non-specific lipid transfer protein
Allergenicity of nut allergens
Cross-reactivities of nut allergens
The following cross-reactions have been identified for peanuts, hazelnuts and cashew nuts:
Component-resolved diagnostics in nut allergy
The potential of component-resolved diagnostics (CRD) in routine diagnostics for peanut and tree nut allergies has been extensively studied.5,28,29
Generally, CRD may offer:
- Detection of species-specific marker allergens which can indicate primary sensitisation, e.g. Cor a 14 (hazelnut) and Ara h 2 (peanut)20
- Discrimination between cross-reactivities which may be causing clinical symptoms, e.g. Bet v 1 (birch) and Cor a 1 (hazelnut) cross-reactivity (very common in birch pollen allergic subjects). This can differentiate pollen-food syndrome from true nut allergy20
- Reduce the number of oral food challenges.28,29
All results must be interpreted with the patient’s medical history and symptoms.30
CRD in peanut and tree nut allergies
Peanuts (Arachis hypogaea)
- Ara h 1, Ara h 2 and Ara h 3 can be used as primary, species-specific sensitisation markers as long as specific IgE to storage proteins from other legumes are negative or significantly lower20. However, in some Mediterranean populations, sensitisation to Ara h 9 may be more prevalent.10
- For example, a cross-sectional study performed in children and adolescents showed that Ara h 9 sensitisation was more frequent in older children (age 6–10) and adolescents (age 11–20) and less frequent in younger children (age 1–5). The opposite trend was observed with Ara h 2.11
- IgE sensitisation to Ara h 5 and Ara h 8 is associated with profilin and PR-10 Bet v 1 cross-reactions, respectively.20
Hazelnuts (Corylus avellane)20
- IgE sensitisation to Cor a 9 and Cor a 14 in hazelnut allergy can be used as primary species-specific allergen markers if specific IgE to storage proteins (2S albumins, 7S and 11S globulins) in other tree nuts, legumes or seeds are significantly lower.
- IgE to sensitisation to Cor a 8 in a food allergic patient (from southern Europe) with systemic reactions can be associated with primary Cor a 8-associated sensitisation or an nsLTP-cross reaction.
- In birch pollen allergic patients (e.g. from central or northern Europe) with mostly mild oral symptoms, cross-reactivity to Cor a 1 is common.
Cashew nuts (Anacardium occidentale)
- Specific IgE to Ana o 3 can be used to predict clinically relevant allergy to cashew nuts.18
Are there scenarios in which CRD results provide clues for predicting the severity of nut allergy response?
- Sensitisation to Ara h 2 is considered to be the best predictor for peanut allergy; however, Ara h 9 may be a better predictive marker in southern European populations
- Sensitisation to peanut allergens Ara h 8 and Ara h 5 can be indicators of cross-reactivity
- Cor a 9 and Cor a 14 are primary species-specific allergen markers for hazelnut; however, sensitisation to Cor a 8 may also be of relevance to southern European patients
- Sensitisation to hazelnut allergen Cor a 1 can be an indicator of cross-reactivity
- Sensitisation to Ana o 3 is considered the best predictor for cashew nut allergy
- CRD can be used to detect sensitisation to species-specific allergen markers for each nut and can be used to distinguish primary nut allergy from pollen-food syndrome.
- CRD may also help reduce the number of oral food challenges carried out.