Background Actinidin has previously been reported as the major allergen in kiwifruit.
Objectives To investigate the relevance of actinidin in a well-characterized population of UK patients with kiwifruit allergy.
Methods To identify the allergens in kiwifruit, using Western blots, we examined the IgE-binding patterns of 76 patients with a history of kiwifruit allergy, 23 of who had had a positive double-blind, placebo-controlled food challenge. In addition, IgE binding to purified native actinidin was studied in 30 patients, and to acidic and basic isoforms of recombinant actinidin in five patients. Inhibition of IgE binding to kiwifruit protein extract by purified native actinidin was investigated by both inhibition immunoblots and inhibition ELISAs using pooled sera.
Results Twelve protein bands in kiwifruit protein extract were bound by IgE. A protein band with a molecular weight of 38 kDa was the major allergen recognized by 59% of the population. IgE did not bind to actinidin in the kiwifruit protein extract, or to purified native or recombinant forms of actinidin during Western blotting. Pooled sera bound to kiwifruit protein extract but not purified actinidin on ELISA, and pre-incubating sera with actinidin did not inhibit IgE binding to kiwifruit protein extract on immunoblot or ELISA.
Conclusion A novel 38 kDa protein, not actinidin, is the major allergen in this large study population. Identification of major allergens in one patient group is therefore not necessarily reproducible in another; therefore, major allergens should not be defined until there is a sufficient body of data from diverse geographical and cultural populations.