Abstract
English walnut (Juglans regia) belongs to the most important allergenic tree nuts. Co-sensitization with birch (Betula verrucosa) pollen has been reported. We aimed to identify a walnut allergen homologous to the major birch pollen allergen Betv1. A cDNA encoding a Betv1-homologous allergen (Jugr5) in walnut kernels was cloned by RT-PCR. Jugr5 was expressed in Escherichia coli, purified by column chromatography and characterized by circular dichroism spectroscopy. Specific IgE levels to walnut, Betv1, and Jugr5 in birch pollen allergics (n = 16) with concomitant walnut allergy were measured by ImmunoCAP: 44% of the patients were tested positive to walnut while 94% were reactive to Jugr5, and 100% to Betv1. Jugr5 and Betv1 allergens showed bidirectional IgE cross-reactivity by competitive ELISA and were capable of inducing histamine release from effector cells. Immunoblot competition experiments demonstrated the presence of IgE-reactive Jugr5 in walnut extract, but at low levels. A Betv1-like allergen was identified in walnut. Diagnostic use of Jugr5 will compensate for the low sensitivity of walnut extract for patients with birch pollen associated walnut allergy.
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