Background: Cashew nut allergy is the second most commonly reported tree nut allergy in the United States. We have previously cloned and characterized major cashew allergens belonging to the vicilin and legumin families of seed storage proteins.
Objective: Here we set out to describe a third major cashew allergen, a 2S albumin.
Methods: The recombinant cashew 2S albumin was amplified from a cDNA library by means of PCR, sequenced, and expressed in Escherichia coli. Immunoblotting was used to screen for reactivity with patients' sera, and inhibition immunoblotting was used to identify the corresponding native cashew nut proteins. The mass of affinity-purified native allergen was determined by means of matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectroscopy. Patients' sera were used to probe solid-phase 2S albumin peptides to identify linear epitopes.
Results: The cloned allergen, designated Ana o 3, was identified as 2S albumin. MALDI-TOF mass spectroscopy of native Ana o 3 yielded a molecular mass of 12,598 d. Immunoblot analysis showed 21 (81%) of 26 sera from patients with cashew allergy were reactive. Three native Ana o 3 large-subunit isoforms with molecular weights ranging from approximately 6 to 10 kd were identified. Probing of overlapping synthetic Ana o 3 peptides with patients' sera identified 16 reactive peptides, 4 of which gave strong signals and one of which positionally overlaps linear epitopes in mustard and walnut allergenic 2S albumins. The overlapping cashew and walnut epitopes also share considerable homology.
Conclusions: We conclude that this 2S albumin protein is a major allergen in cashew nut and demonstrates a possible basis for cross-reactivity with walnut 2S albumin.