Occupational asthma caused by soybean flour in bakers - differences with soybean-induced epidemic asthma

Background Soybean dust has been identified as the causative agent of occup ational asthma and asthma epidemics. Two main soybean hull allergens respon sible for asthma outbreaks, Gly m 1 and Gly m 2, have been identified and p urified. Objective The soybean allergens causing occupational asthma in exposed bake rs were investigated and compared with those involved in epidemic asthma. Methods We report four bakers or confectioners with work-related respirator y symptoms who were exposed to soybean flour used as a baking additive. The causative role of soybean flour was investigated by immunological tests an d specific inhalation challenge tests. Soybean flour allergens causing occu pational asthma were characterized by immunoblotting. Immunoglobulin (Ig) E -reactivity to Gly m 1 and Gly m 2 was assessed using enzyme-linked immunos orbent assay. Results Sensitization to soybean flour was demonstrated by skin and serolog ical tests and was confirmed by positive inhalation tests. Bronchial challe nge test to soybean flour extract elicited immediate or dual asthmatic resp onses. Immunoblotting with soybean flour and soybean hull extracts showed I gE-binding mainly to high molecular weight (MW) allergens. There was an imp ortant individually different allergic response to inhalant soybean compone nts. None of the patients showed IgE-reactivity against Gly m 1 and only on e patient showed IgE-reactivity to the soybean hull allergen Gly m 2. Conclusion These bakery workers had developed IgE-mediated occupational ast hma to soybean flour. The allergens involved in occupational asthma caused by soybean flour are predominantly high MW proteins that are present both i n soybean hull and flour, and they are different from the allergens causing asthma outbreaks, which are mainly low MW proteins concentrated in the hul l.