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Severe walnut allergies in children caused by storage proteins

Published online: January 29, 2019
Walnut is thought to be a main trigger of food allergy to tree nuts causing a high rate of anaphylactic reactions. Systematic studies evaluating the clinical relevance of individual walnut allergens have not been performed, and immunotherapy of walnut allergy has not been established in clinical practice.  
In a recent clinical study published in The Journal of Allergy and Clinical Immunology: In Practice, Ballmer-Weber and collaborators recruited adults and children with walnut allergy from Switzerland, Spain, and Germany. Walnut allergy was confirmed by food challenge tests provided that the severity of the allergy allowed for the testing. The presence of IgE antibodies specific for a comprehensive panel of ten walnut protein components or protein fractions was tested in blood samples, both from allergic and control subjects. Furthermore, skin tests (prick tests) with various allergen extracts were performed. In total, 91 walnut allergic subjects and 24 controls were included.
The researchers found that sensitization to walnut storage proteins as a rule occurs in childhood and is associated with severe allergy symptoms. Apart from one allergen (rJug r 5), levels of the specific IgE against walnut extracts and walnut components were higher in study participants younger than 14 years of age than in older participants. Furthermore, all participants younger than 14 years of age developed severe allergy symptoms whereas 38 percent of the study participants aged 14 and above showed only mild reactions. Those with severe allergy symptoms showed higher specific IgE levels against walnut extract and against some of the walnut components studied. In particular, high IgE levels to the 2S albumin Jug r 1 and to high and low molecular weight vicilin fractions (Jug r 2 and Jug r 6), but not to non specific lipid transfer protein (Jug r 3) and the pathogenesis-related protein 10 (Jug r 5) correlated with systemic reactions to walnuts.  
Walnut allergy is an important and prevalent tree nut allergy associated with severe allergic symptoms. The study provides information on the relative importance of all known walnut allergens across Europe and evidence suggesting that vicilins may be as important as 2S albumin in walnut allergy. Patients with early onset walnut allergy have an elevated risk of severe reactions and should be given particular attention by clinicians. Vicilins and 2S albumin may serve as risk marker and targets for developing immunotherapy of food allergy to walnuts

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.