Detection and clinical characterization of patients with oral allergy syndrome caused by stable allergens in Rosaceae and nuts

Background: A minority of patients with oral allergy syndrome (OAS) induced by Rosaceae or nuts are positive on skin prick tests with commercial food extracts. This suggests reactivity against distinct stable allergens. Objectives: (1) To define the prevalence of subjects positive on skin prick tests with commercial extracts among patients with OAS caused by Rosaceae and/or nuts and (2) To investigate whether commercial extracts-positive subjects show some peculiar clinical feature and may represent a specific subset with food allergy. Methods: Skin prick tests were carried out with a large panel of commercial extracts of airborne allergens (Allergopharma) and of vegetable foods (Dome/ Hollister-Stier) in 298 adults with OAS caused by Rosaceae (n = 237) and or nuts (n = 161), positive on skin prick tests with fresh offending foods. Results: 25/237 (11%)patients were positive on prick tests with commercial plum extract. This subgroup showed a higher incidence of systemic symptoms (64% versus 6%; P <.001) and a lower incidence of birch pollen allergy (12% versus 99%; P <.001) than commercial extract-negative patients; moreover, 36% versus 0%, respectively, did not have respiratory allergy (P <.001). Apple and peach were the main offending foods among commercial extract-negative and commercial extract-positive patients, respectively (87% versus 44% for apple, P <.001; and 52% versus 88% for peach, P <.005). Eight of one hundred sixty-one (5%) nuts-sensitive patients were positive on prick test with commercial walnut extract. This subgroup showed a higher proportion of patients who experienced systemic symptoms ((63% versus 6%, P <.001), a lower prevalence of birch pollen allergy (13% versus 97%, P <.001), and a higher prevalence of grass pollen allergy (88% versus 41%, P <.05) than commercial extract-negative subjects. Further, reactivity against commercial walnut extract was associated with skin reactivity against commercial extracts of peanut (88% versus 37%, P <.005), tomato (75% versus 5%, P <.001), and plum (63% versus 8%, P <.001), and inversely related with skin reactivity against fresh apple (P <.001). In most cases, high levels of IgE specific for peach, apple, and hazelnut were associated with peanut reactivity rather than with clinical sensitivity to specific foods. In a preliminary investigation, most commercial extract-positive patients reacted against a 10-kDa protein characterized as a lipid transfer protein (LTP). Conclusions: Skin prick tests with commercial extracts of plum and walnut may be usefully employed to detect patients with OAS reacting against stable allergens. The high prevalence of systemic symptoms in these patients suggests that allergens' stability is associated with a higher resistance to the gastrointestinal environment and strongly influences the clinical expression of vegetable food allergy. At least some stable allergens, namely lipid transfer protein might be shared by botanically unrelated fruits such as nuts, peanuts, legumes, tomato, and Prunoideae.