Soybean beta-conglycinin as the main allergen in a patient with food-dependent exercise-induced anaphylaxis by tofu: food processing alters pepsin resistance

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 beta-conglycinin mainly reacts with IgE antibodies in the patient's serum. By immunoblot analysis, beta-conglycinin in soy milk completely disappeared after pepsin digestion within 20 min, whereas beta-conglycinin in tofu was almost intact after more than 120 min of pepsin digestion.

CONCLUSION

We identified beta-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.

Two cases of pollen-food allergy syndrome to soy milk diagnosed by skin prick test, specific serum immunoglobulin E and microarray analysis

Oral allergy syndrome to soy milk is classified as a phenotype of pollen-food allergy syndrome (PFAS). As causative antigens, Gly m 4 (Bet v 1 homolog, 17 kD) and oleosin (23 kD), have been reported. In this study, we report two cases of PFAS to soy milk. Both cases showed positive reactions to soy milk in skin prick tests (SPT) and to Gly m 4 in specific serum immunoglobulin (Ig)E antibody. When we measured specific serum IgE antibody of soy-related proteins using a new laboratory testing method, microarray analysis, both cases showed a positive reaction for Bet v 1. One case was weakly positive for a soybean protein, beta-conglycinin. Other results for reactivity to soy, peanut, cross-reactive carbohydrate determinants and profilin were negative. Based on these results, we diagnosed the two cases as PFAS to Gly m 4. We also performed protein microarray analysis and found it useful as a screening test for immediate allergy, such as PFAS.