NEOALLERGENS IN HEATED SOYBEAN HULL

Background: During the process of harvest, transport and storage, micr obial and mold contamination can raise the temperature of soybeans to 75 degrees C or higher. The purposes of this study were (1) to evaluat e the allergenicity of fresh and stored soybean hulls and (2) to ascer tain whether heat alters the allergenicity of stored soybean hulls. Me thods: Allergen extracts were prepared from (1) stored soybean hulls, (2) fresh soybean hulls and (3) stored soybean hulls heated to 37 degr ees C (El), 55 degrees C (E2) and 80 degrees C (E3) or kept at room te mperature (E4) for 16 h. Individual serum from 68 soybean asthmatic (S A) subjects, 30 nonallergic subjects and two serum pools made from 4 S A sera and 4 sera from asthmatics not sensitive to soybean were studie d. All sera and serum pools were assayed for content of specific IgE ( radioallergosorbent test) and IgG4 (ELISA). The following additional s tudies were done for extracts E1-E4: (1) SDS-PAGE, (2) SDS-PAGE/Wester n blot for specific IgE and IgG4 using both serum pools, and (3) study of the effects of heat on inhibiting activity of the extracts prepare d from stored soybean hulls using the pool of SA sera. Results: Test r esults demonstrated a reduced binding of specific IgE and IgG4 to fres h soybean hull extract compared to stored soybean hull extract, and an increased binding for heated extracts (E1-E3) compared to unheated on es (E4), Moreover, there was an increase in potency for IgE and IgG4 b indings for the heated (E1-E3) compared to unheated (E4) extract, as m easured by the amount of protein to produce 50% inhibition. Several pr otein bands with a molecular weight (MW) higher than 20 kD were absent from the SDS-PAGE for E3 but were present in El, E2 and E4, and a new protein band (MW 15.3 kD) appeared for E3 only. Two new protein bands , with MWs of 15.3 and 10 kD, which bind specific IgE, were present on Western blot and one of the 3 main soybean hull allergens, probably G ly m 2, disappeared in E3. IgG4 Western blot showed similar results, b ut only the 10 kD protein band was present. Conclusion: The results de monstrate that soybean hull allergenicity is affected by heat, and sug gest that the heat generated during storage and transport of soybeans could generate 2 new allergen determinants or increases in epitope exp osure as a result of conformational changes. The significance of these new IgE and IgG4 binding proteins has yet to be determined.