Anaphylaxis caused by the ingestion of cultivated mushroom (Agaricus bisporus): Identification of allergen as mannitol

Background: The role of mushroom spores as inhalants in causing respiratory allergy has been well established. Although mushrooms are commonly used as food throughout the world, food allergy to mushrooms is not very common. A severe case of anaphylaxis in a 32-year-old woman who experienced facial edema and generalized urticaria minutes after eating mushroom curry is presented herein. The purpose of the present study was to identify the putative allergen in the cultivated mushroom Agaricus bisporus. Methods: A combination of biochemical fractionation/analytical techniques (gel filtration, ultrafiltration, ion-moderated cation-exchange chromatography, high-pressure liquid chromatography and gas chromatography-mass spectrometry (GC-MS)) and allergy diagnostic tests (skin prick test (SPT), allergen-specific IgE) were used. Results: The SPT with mushroom extract was strongly positive; however, allergen-specific IgE could not be detected by enzyme-linked immunosorbent assay. The SPT was also positive with cooked, steamed or dried mushroom extracts, suggesting the presence of a heatstable allergen. Gel filtration of mushroom extract on Sephadex G-25, as analyzed by SPT, indicated the presence of a low molecular weight (< 1 kDa) allergen. Using ion-moderated cation-exchange chromatography, the allergen was isolated and identified as mannitol based on skin reactivity. Mannitol was confirmed by GC-MS analysis. Conclusions: This is the first report of food allergy to cultivated mushroom A. bisporus and also the first report describing a low molecular weight allergen (mannitol) in mushroom.