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* Division of Immunopathology, Department of Pathophysiology, Center of Physiology, Pathophysiology, and Immunology, Medical University of Vienna, Vienna;
Max F. Perutz Laboratories, University of Vienna, Vienna;
Department of Molecular Biology, Division of Allergy and Immunology, University of Salzburg, Salzburg, Austria;
Allergy Department Fundación Jiménez Díaz, Universidad Autónoma de Madrid, Madrid, Spain;
¶ Institute of Medical Physics and Biophysics, University of Münster, Münster, Germany; and
|| Center for Clinical and Experimental Allergology, Istituto Dermopatico dell'Immacolata-Istituto di Ricovero e Cura a Carattere Scientifico, Rome, Italy
IgE-mediated sensitization to wheat flour belongs to the most frequent causes of occupational asthma. A cDNA library from wheat seeds was constructed and screened with serum IgE from baker's asthma patients. One IgE-reactive phage clone contained a full-length cDNA coding for an allergen with a molecular mass of 9.9 kDa and an isoelectric point of 6. According to sequence analysis it represents a member of the potato inhibitor I family, a group of serine proteinase inhibitors, and thus is the first allergen belonging to the group 6 pathogenesis-related proteins. The recombinant wheat seed proteinase inhibitor was expressed in Escherichia coli and purified to homogeneity. According to circular dichroism analysis, it represented a soluble and folded protein with high thermal stability containing mainly β-sheets, random coils, and an 
-helical element. The recombinant allergen showed allergenic activity in basophil histamine release assays and reacted specifically with IgE from 3 of 22 baker's asthma patients, but not with IgE from grass pollen allergic patients or patients suffering from food allergy to wheat. Allergen-specific Abs were raised to localize the allergen by immunogold electron microscopy in the starchy endosperm and the aleuron layer. The allergen is mainly expressed in mature wheat seeds and, despite an 
50% sequence identity, showed no relevant cross-reactivity with allergens from other plant-derived food sources such as maize, rice, beans, or potatoes. Recombinant wheat serine proteinase inhibitor, when used in combination with other specific allergens, may be useful for the diagnosis and therapy of IgE-mediated baker's asthma.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by a research grant from Phadia, Uppsala, Sweden, and by Grant F1815 of the Austrian Science Fund, Fonds zur Förderung der Wissenschaftlichen Forschung.
2 Address correspondence and reprint requests to Dr. Rudolf Valenta, Christian Doppler Laboratory for Allergy Research, Division of Immunopathology, Department of Pathophysiology, Center of Physiology, Pathophysiology and Immunology, Medical University of Vienna, Vienna General Hospital, Waehringer Guertel 18-20, 1090 Vienna, Austria. E-mail address: rudolf.valenta{at}meduniwien.ac.at
3 Abbreviations used in this paper: RAST, radioallergosorbent test; CD, circular dichroism; PR, pathogenesis related; RBL, rat basophil leukemia.
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