In vitro evaluation of allergenicity of dried food powders manufactured for food provocation test]

Food provocation test (FPT) is one of important diagnostic methods for food allergy, but no standard antigens for FPT have yet been developed. In this study, dried powders were manufactured from five kinds of foods (cow's milk, hen egg, chicken, soybean and wheat) by spray-drying or freeze-drying and examined in vitro for their usefulness as antigens for FPT. In SDS-PAGE, the migration pattern of the extract from each powder was the same as or closely similar to that of the extract from its material. When analyzed by ELISA, a good correlation (r=0.853-0.978) in the reactivity with sera from food-allergic patients was observed between the extracts from each powder and its material. Moreover, in cow's milk, hen egg and soybean, almost the same ELISA inhibition curves were drawn, regardless of whether the extracts from each powder and its material were used as immobilized antigens or inhibitors. These results demonstrated that each powder contains the same allergens as its material at almost the same levels, being useful as an antigen for FPT. Favorably, the powders were found to be stored without significant changes in IgE reactivity at -20 degrees C or 5 degrees C for more than 18 months, although their storage at room temperature was suggested to be avoided.