A case of systemic peach allergy without sensitization to gibberellin-regulated protein and lipid-transfer protein: identification of FKBP20-1 as a potential allergen

Peach allergy is a common plant food allergy; specifically, sensitization to gibberellin-regulated protein (GRP; Pru p 7) and lipid-transfer protein (LTP; Pru p 3) is considered a predictor of severe allergic reactions in patients with peach allergy. However, the allergenic mechanisms in patients who are negative for these components remain unclear. Herein, we report the case of a 26-year-old Japanese man with a history of atopic dermatitis and pollinosis. The patient developed systemic allergic symptoms, including oral pruritus, pharyngeal swelling, respiratory discomfort, palpitations, and pallor, after ingesting a whole raw peach. Specific immunoglobulin E (IgE) to peach extract and Pru p 1 was positive, whereas specific IgE to Pru p 3, Pru p 4, and Pru p 7 was negative. Skin prick testing was positive for raw peach but negative for purified peach GRP. A proteomic approach was used to identify causative allergens. Two-dimensional electrophoresis and immunoblotting revealed an IgE-binding protein spot at approximately 25 kDa. Mass spectrometry identified the protein as peptidyl-prolyl cis-trans isomerase FKBP20-1 (FKBP20-1). Recombinant FKBP20-1 showed strong IgE reactivity with the patient’s serum but not with sera from nonallergic controls. Therefore, FKBP20-1 may represent a potential IgE-binding allergen involved in systemic reactions to peaches in patients who are not sensitized to GRP or LTP. Further studies are needed to clarify the clinical relevance of these findings.