Comparison of IgE Binding Capacity and Expression Analysis of Strawberry Allergen Fra a 1

Oral allergy syndrome (OAS) is usually caused by an allergy to fresh fruits. It is an immunoglobulin E (IgE)-mediated immediate allergy localized in the oral mucosa, and the characteristics depend on the lability of the antigen (Kondo and Urisu, 2009). Consumption of strawberries (Fragaria × ananassa) can cause OAS, primarily because of the presence of proteins, such as Fra a 1–4, which cross-react to the birch pollen allergen Bet v 1. To produce strawberries with low allergen content, the expression patterns of proteins with high IgE binding activity should be demonstrated. In this study, we compared the allergenicity of Fra a proteins, estimated their stress inducibility, and investigated their expression during fruit (receptacles and achenes) ripening. His-tagged proteins were purified and their reactivity to IgE from six birch pollen-allergic patients was analyzed by western blotting. Homology searches were carried out on EST libraries of Fragaria vesca produced under several stress conditions. Fruits of F. × ananassa were harvested at seven different ripening stages. For salt-stress treatments, fruits were soaked in 150 mM NaCl for 1–24 h. Real-time PCR was carried out using primers to detect Fra a 1. The IgE binding capacity of Fra a 1 was higher than those of the other Fra a isoforms. In F. vesca, the expression of Fra v 1, which has the same sequence as Fra a 1, seemed to be higher than the other paralogs and was especially induced by salt stress. In F. × ananassa, Fra a 1 expression in fruits was highest at the early stage of ripening and decreased to 1/70^th this level as maturation progressed to the red-colored stage, but increased beginning 5 hours after salt-stress treatment, suggesting that fruit allergenicity can be increased by environmental stimuli. These results indicated that Fra a 1 plays an important role in determining the allergenicity of strawberry fruit, and its expression is affected by environmental conditions such as salt stress. This work was supported by the Hyogo Alliance of Universities and Colleges for Innovation and by JSPS KAKENHI Grant Number 24658030.