Identification of the soybean hull allergens responsible for the Barcelona asthma outbreaks

Background: Soybean hulls were identified as the etiologic agent responsible for the asthma outbreaks that occurred in Barcelona and Cartagena, Spain. Objective: To identify the main soybean hull allergens using the sera of 18 asthmatic epidemic patients from Barcelona and to compare the results to those previously reported. Methods: Specific IgE to a soybean hull allergen extract was determined by radioimmunoassay and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in a 10-20% Tris-tricine gradient gel followed by Western blot. Results: Specific IgE, which was detected in 15 of the 18 (83.3%) sera, indicated two nonoverlapping band patterns on the SDS-PAGE/Western blot: (1) pattern 1, present in 11 sera, consisted of three bands with estimated molecular weights (MWs) of 8, 7.5 and 7 kD, which are the MWs described for the allergens Gly m 2, Gly m 1A and Gly m 1B, respectively, and (2) pattern 2, present in 3 sera, consisted of a band with an estimated MW of 8.2-8.3 kD and four additional bands in a MW range of 25-36 kD, The remaining positive sera indicated very faint bands. Conclusions: This study confirms that soybean hulls contain three main allergens with MWs of 8, 7.5 and 7 kD, and indicates additional higher MW allergens, which selectively bind specific IgE of the sera that do not react with the three low MW components. This dichotomous and nonoverlapping pattern of allergen recognition has not been previously described.