Molecular and immunological characterization of a wheat serine proteinase-inhibitor as a novel allergen in baker's asthma

Background:

Immunoglobulin E-mediated sensitization to wheat flour belongs to the most frequent causes of occupational asthma.

Methods:

In order to identify allergens involved in baker's asthma we have constructed a cDNA library from wheat seeds and screened the library with serum IgE from patients with baker's asthma. The recombinant allergen was expressed in Escherichia coli and purified to homogeneity.

Results:

One phage clone specifically recognized by baker's asthma patients contained a full length cDNA coding for an allergen with a molecular weight of 9.9 kDa and a pI of 6 which according to sequence analysis could be identified as a member of the potato inhibitor I family, a group of serine proteinase inhibitors conserved throughout the plant and animal kingdom. According to circular dichroism analysis it represented a soluble and folded protein containing mainly β-sheets, random coils and an alpha helical element and high thermal stability. The recombinant allergen showed allergenic activity and reacted specifically with IgE from bakers' asthma patients but not with IgE from grass pollen allergic patients or patients suffering from food allergy to wheat. Using allergen-specific rabbit antibodies it is demonstrated that the protein is mainly expressed in mature wheat seeds and, despite an overall degree of approximately 50% sequence identity, showed no relevant cross-reactivity with plant food sources such as maize, rice, bean or potato.

Conclusion:

Recombinant wheat serine proteinase inhibitor may be useful for the diagnosis and therapy of IgE-mediated baker's asthma.