Soybean flour asthma: detection of allergens by immunoblotting

A 43-year-old woman developed asthma 6 years after beginning work in a food-processing plant in which soybean flour was used as a protein extender. Symptoms of sneezing, coughing, and wheezing would begin within minutes of exposure to soybean flour and resolve 2 hours after exposure ceased. Skin tests were positive to a soy extract prepared from the flour. Airway hyperreactivity was confirmed by a positive bronchial challenge to methacholine. Bronchial challenge with soybean flour produced an immediate increase in specific airway resistance from 5.0 to 22.7 L. cm of H2O/L/sec. There was no response to challenge with lactose. The patient's allergic response to soy-flour extract was further characterized by several immunologic methods. IgE binding to soy-flour protein by direct RAST was 5.98 times that of a normal control serum. The soy-flour extract was separated by dodecyl sulfate-polyacrylamide gel electrophoresis. Twenty-four protein bands were detected in the crude soy-flour extract. After immunoblotting and subsequent autoradiography, nine proteins with molecular weights ranging from 54,500 to 14,875 were found. Cross-reactivity studies with other legumes demonstrated apparent immunologic identity between a component in green pea extract and a soybean protein with a molecular weight of 17,000. The clinical significance of this cross-reactivity is not known. We conclude that in this case of occupational asthma to soybean flour, multiple allergens were involved. Immunoblotting may be useful in identifying the allergens involved in occupational asthma.