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S1-Casein, a Major Cow’s Milk Allergen1
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* Institute of Medical and Chemical Laboratory Diagnostics,
Department of Pathophysiology, Division of Immunopathology, Center for Physiology and Pathophysiology, and
Christian Doppler Laboratory for Allergy Research, Medical University of Vienna, Austria;
Phadia, Uppsala, Sweden;
¶ Department of Molecular Biology, Division of Allergy and Immunology, University of Salzburg, Austria;
|| Institute for Chemistry, Structural Biology, Karl-Franzens-University, Graz, Austria;
# Department of Pediatric Allergology and Pneumology, Hedwig-von-Rittberg-Zentrum, German Red Cross Hospital Westend, Berlin, Germany;
** Hospital La Paz, Allergy Department, Madrid, Spain;
Allergy Clinic Reumannplatz, Vienna, Austria;
* Division of Immunopathology, Department of Pathophysiology, Center for Clinical and Experimental Allergy, Istituto Dermopatico dell’Immacolata-Istituto di Ricovero e Cura a Carattere Scientifico, Rome, Italy;
* Service de Pneumologie, Hôpitaux Universitaires, Strasbourg, France; and
* Mead Johnson Nutritionals, Evansville, IN 47712
Milk is one of the first components introduced into human diet. It also represents one of the first allergen sources, which induces IgE-mediated allergies in childhood ranging from gastrointestinal, skin, and respiratory manifestations to severe life-threatening manifestations, such as anaphylaxis. Here we isolated a cDNA coding for a major cow’s milk allergen, 
S1-casein, from a bovine mammary gland cDNA library with allergic patients’ IgE Abs. Recombinant S1-casein was expressed in Escherichia coli, purified, and characterized by circular dichroism as a folded protein. IgE epitopes of S1-casein were determined with recombinant fragments and synthetic peptides spanning the S1-casein sequence using microarrayed components and sera from 66 cow’s milk-sensitized patients. The allergenic activity of rS1-casein and the S1-casein-derived peptides was determined using rat basophil leukemia cells transfected with human Fc
RI, which had been loaded with the patients’ serum IgE. Our results demonstrate that rS1-casein as well as S1-casein-derived peptides exhibit IgE reactivity, but mainly the intact rS1-casein induced strong basophil degranulation. These results suggest that primarily intact S1-casein or larger IgE-reactive portions thereof are responsible for IgE-mediated symptoms of food allergy. Recombinant S1-casein as well as S1-casein-derived peptides may be used in clinical studies to further explore pathomechanisms of food allergy as well as for the development of new diagnostic and therapeutic strategies for milk allergy.
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 Grants F01804, F0105, and F01815 from the Austrian Science Foundation and by a research grant from Biomay, Vienna, Austria.
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, Waehringer Guertel 18-20, 1090 Vienna, Austria. E-mail address: rudolf.valenta{at}meduniwien.ac.at
3 Abbreviations used in this paper: CD, circular dichroism; kUA/L, kilounits allergen-specific IgE per liter; RBL, rat basophil leukemia.
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