Cloning, Expression, and Mapping of Allergenic Determinants of αS1-Casein, a Major Cow’s Milk Allergen

Abstract

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, αS1-casein, from a bovine mammary gland cDNA library with allergic patients’ IgE Abs. Recombinant αS1-casein was expressed in Escherichia coli, purified, and characterized by circular dichroism as a folded protein. IgE epitopes of αS1-casein were determined with recombinant fragments and synthetic peptides spanning the αS1-casein sequence using microarrayed components and sera from 66 cow’s milk-sensitized patients. The allergenic activity of rαS1-casein and the αS1-casein-derived peptides was determined using rat basophil leukemia cells transfected with human FcεRI, which had been loaded with the patients’ serum IgE. Our results demonstrate that rαS1-casein as well as αS1-casein-derived peptides exhibit IgE reactivity, but mainly the intact rαS1-casein induced strong basophil degranulation. These results suggest that primarily intact αS1-casein or larger IgE-reactive portions thereof are responsible for IgE-mediated symptoms of food allergy. Recombinant αS1-casein as well as αS1-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.

Molecular and Immunological Characterization of Tri a 36, a Low Molecular Weight Glutenin, as a Novel Major Wheat Food Allergen

“…Rat basophil leukemia (RBL) assays were performed as described (27). RBL cells (clone RBL-703/21) transfected with the human FcεRI (28) were incubated with sera (diluted 1:20) from two wheat food-allergic patients (nos.…”

Expression of a Biologically Active GFP-αS1-Casein Fusion Protein in Lactococcus lactis

“…It also represents one of the first allergen sources, which induces immunoglobulin E (IgE)-mediated allergies in childhood ranging from gastrointestinal, skin, and respiratory manifestations to severe life-threatening manifestations, such as anaphylaxis [18]. Cow's milk allergy is the most common food allergy in young children, affecting 1-2% of all infants [18].…”

“…It also represents one of the first allergen sources, which induces immunoglobulin E (IgE)-mediated allergies in childhood ranging from gastrointestinal, skin, and respiratory manifestations to severe life-threatening manifestations, such as anaphylaxis [18]. Cow's milk allergy is the most common food allergy in young children, affecting 1-2% of all infants [18]. Casein represents a major allergen in cow's milk [3] and consists of four proteins: α S1 -casein, α S2 -casein, β-casein and κ-casein, representing 32%, 10%, 28%, and 10%, respectively, of the total milk protein [17].…”

Allergenicity of Milk Proteins

“…These results suggest that primarily intact αs1-CN or larger IgE-reactive portions thereof are responsible for IgE-mediated symptoms of FA [49]. …”