Germin-like protein Cit s 1 and profilin Cit s 2 are major allergens in orange (Citrus sinensis) fruits.

Background: Oranges are clinically relevant allergenic foods. Well-documented studies in IgE-mediated orange allergy and characterization of allergens are still lacking. Objective: To analyze the sensitization profile in orange sensitized subjects with and without clinical allergy, and to identify relevant orange allergens. Methods: 56/82 of sensitized subjects with self-reported reactions to orange were grouped into reactors (anaphylaxis or multiple episodes of immediate reactions and/or OFC+) and non-reactors (OFC-). Allergens were identified by IgE-immunoblotting, N-terminal sequencing and IgE-inhibition assays. Mediator release assays were performed to determine the allergenic potency of orange profilin. Results: 8/24 tested subjects were OFC+. 23/56 subjects were classified as orange allergic showing mainly OAS. 22/23 orange allergic patients were sensitized to profilin, Cit s 2. In patients with mono-sensitization to Cit s 2 in vitro histamine releases up to 75% from basophils was induced using orange extract and recombinant plant profilins. 78% of allergic patients were sensitized to a newly identified allergen of 25 kDa, Cit s 1 a germin-like protein. Both allergens showed retained IgE-reactivity in a heat-processed orange juice. More than 70% of orange allergic patients were sensitized to CCDs. No difference in the allergogram was observed between orange sensitized subjects with and without clinical allergy. Conclusions: Cit s 1 and Cit s 2 are major orange allergens. The potential clinical relevance of orange profilin was indicated by its strong capacity to release histamine from basophils. However, a predominant sensitization to both allergens in subjects without symptoms also indicates a high frequency of clinically insignificant sensitization.