Background Food-dependent exercise-induced anaphylaxis (FDEIA) due to soybeans is a rare disorder. The allergen responsible for FDEIA due to soybeans has not yet been determined.
Objective We characterized the clinical features of a patient with FDEIA due to tofu, who was well tolerant to drinking soy milk. We then sought to identify the responsible soybean allergen(s) in that patient. We further studied whether different stabilities of the allergen(s) to pepsin digestion between two soybean products are related to their clinical allergenicity.
Methods Skin prick tests and provocation tests using soybean products were performed to detect the responsible food and other factors that induced the allergic symptoms. Specific IgE to various soybean allergens were examined by ImmunoCAP®, ELISA and protein microarray assays. Immunoblotting for soybeans and soybean products using the patient's serum was also performed. Soybean products were serially digested by pepsin to disclose the stability of the allergens.
Results Provocation with ingestion of tofu and exercise induced the allergic symptoms, while ingestion of soy milk and exercise did not. Immunoblot analysis, ELISA and protein microarray assay revealed that β-conglycinin mainly reacts with IgE antibodies in the patient's serum. By immunoblot analysis, β-conglycinin in soy milk completely disappeared after pepsin digestion within 20 min, whereas β-conglycinin in tofu was almost intact after more than 120 min of pepsin digestion.
Conclusion We identified β-conglycinin as the causative allergen in a patient with FDEIA induced by tofu. The difference in resistance to pepsin digestion between tofu and soy milk suggests that the presence of undigested allergens in the digestive tract is a prerequisite for the development of FDEIA.