000187 - Identification of a 25 kDa allergen in Orange

The orange (Citrus sinensis) is a widely consumed fruit. There are few reported cases of orange allergy, most of which occur alongside cofactors such as exercise. The main allergens found in oranges are Cit s 1 (germin) and Cit s 2 (profilin). Here, we present a paediatric case of anaphylaxis to orange, in which molecular analysis identified an alternative major allergen: a 25kDa germin-like protein.

We present the case of an 11-year-old boy who has experienced urticaria after eating certain fruits, especially oranges and mandarins, and after handling plants and fruit in the school garden. He currently avoids oranges and other citrus fruits. Orange peel, pulp and juice protein extracts were prepared, followed by SDS-PAGE and IgE-Western blot analysis under reducing and non-reducing conditions. Molecular analysis also included a skin prick test, specific IgE results and an oral provocation test with orange.

The prick test results were positive for orange peel and pulp, and LTP. However, sIgE was only positive for Pru p 1 (PR-10), Act d 2 (TLP), and orange extract (specific IgE) y negative Prup3 (LTP) y Prup7 (GRP). The oral provocation test also yielded a positive result for orange (anaphylaxis). Western blot analysis revealed consistent IgE binding to a 25kDa protein in all orange extracts, particularly in the peel, under both reducing and non-reducing conditions. The molecular weight suggest the presence of Cis s 1, a germin-like glycoprotein recognised as the major allergen of Citrus sinensis in European populations. No IgE binding was observed at molecular weights corresponding to typical panallergens which confirms their lack of involvement in this patient.

We identified a 25 kDa protein, likely to be a germin-like protein (Cis s 1), as the allergen responsible for anaphylaxis to orange in a child with negative results for LTP, profilin, and GRP. Molecular allergen profiling was essential in reconciling the clinical history with the results of the diagnostic tests, highlighting the molecular characterisation of citrus allergies.