Background Sensitization to soybean hull (SH) allergens occurs in subjects from Argentina, a soybean producer country. However, the causative allergens have not been identified. The purposes of this study are to: (i) identify the SH allergens using sera of 29 subjects with asthma and/or allergic rhinitis from Argentina exposed to soybean dust who have a positive (weal with SH/weal with histamine ≥ 0.5) skin prick test to SH; and (ii) determine the N-terminal amino acid sequence of a major 50 K SH allergen that sensitizes this population.
Methods All sera were assayed for specific IgE (RIA), IgG4 (ELISA), and IgE and IgG4-Western blots. A sera pool from 10 healthy subjects was a negative control. N-terminal amino acid sequencing was performed by the Edman degradation method.
Results Positive specific IgE only was found in 12/29 (41.4%), IgG4 in 3/29 (10.3%), and both IgE and IgG4 in 14/29 (48.3%) sera. IgE-Western blot demonstrates: (i) an allergen, MW 50 K (51.7% binding); (ii) one or two distinct allergens, MW < 20.2 K (72.4% binding), depending on the sera; and (iii) 1–5 additional IgE binding proteins, MW > 20.2 to < 46.9 K (41.4% binding), depending on the sera. IgG4-Western blot demonstrates: (i) a band, MW 70K (31% binding); (ii) a band, MW 50 K (17.2% binding); (iii) one or two additional bands, MW < 20.2 K (51.7% binding), depending on the sera; and (iv) a band, MW > 20.2 to < 28.5 K (20.7% binding). The 50 K allergen N-terminal amino acid sequence of the first 17 amino acids indicates a significant homology with chlorophyll A-B binding protein precursors from tomato, spinach, and petunia.
Conclusions Specific IgE and IgG4 to SH are common in sera from allergic individuals living in rural areas in Argentina. SH contain an IgE binding protein, MW about 50 K, not previously described. Sensitization to this allergen is common in subjects who are repeatedly exposed to soybean dust inhalation.