Background: Allergy to fig fruit (Ficus carica) has been described in patients allergic to Ficus benjamina or rubber latex but may occur also in pollen-allergic patients.
Objective: To study the potential cross-reactivity between fig and taxonomically related fruits with the major birch pollen allergen Bet v 1.
Methods: One hundred and eighty-eight patients with or without birch pollen allergy were prick-to-prick tested with fig (F. carica), mulberry (Morus alba), jackfruit (Artocarpus heterophyllus; all family Moraceae) and other pollen-associated foods. Moraceae fruit extracts were separated by SDS-PAGE and tested with patient sera and polyclonal antisera against Mal d 1. Western blot inhibition was performed with Moraceae fruit extracts, birch pollen and recombinant Bet v 1. Putative Bet v 1 homologs in Moraceae fruits were analysed by liquid chromatography-ion trap mass spectrometry.
Results: Among 85 patients with isolated birch pollen allergy, 78% had a positive skin test to fresh fig, 10% to dried fig, 91% to mulberry, 91% to jackfruit, 77% to Rosaceae fruits and 83% to hazelnut. Sixty-six per cent of birch pollen-allergic patients positive for fig, reported symptoms after consumption of fresh figs, whereas dried figs were mostly well tolerated. In 60 patients with isolated Ficus benjamina sensitization, the reactivity rates to the same foods were 83-40-0-0-0-0%. None of 32 mugwort pollen-allergic patients reacted to Moraceae fruits. Rabbit anti-Mal d 1 and patient sera reacted to a 17 kDa band in all Moraceae extracts. IgE binding to these proteins was completely inhibited by birch pollen and rBet v 1. Mass spectrometry identified several peptides from the 17 kDa fig, mulberry and jackfruit allergen with respectively 60%, 56% and 76% homology to Bet v 1.
Conclusion: Fig and other Moraceae fruits contain allergens homologous to Bet v 1 and represent clinically relevant birch pollen-associated foods.