Clin Exp Immunol. 2002 Oct;130(1):49-58.
Detection and identification of a soy protein component that cross-reacts with caseins from cow's milk.
Rozenfeld P, Docena GH, Añón MC, Fossati CA.
Cátedra de Inmunología, Facultad de Ciencias Exactas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina.
[ Free full text ]

Soy-based formulas are the most employed cow's milk substitutes in the treatment of cow's milk allergy in our country. Since adverse reactions have been reported in allergic patients as a consequence of exposure to soy proteins, we have investigated the possible cross-reactivity between components from soybean and cow's milk. A cow's milk specific polyclonal antiserum and casein specific monoclonal antibodies were used in immunoblotting and competitive ELISA studies to identify a 30-kD component from soybean that cross-reacts with cow's milk caseins. Its IgE binding capacity was tested by EAST, employing sera from cow's milk allergic patients, not previously exposed to soy proteins. The 30 kD protein was isolated and partially sequenced. It is constituted by two polypeptides (A5 and B3) linked by a disulphide bond. The protein's capacity to bind to the different antibodies relies on the B3 poly-peptide. These results indicate that soy-based formula, which contains the A5-B3 glycinin molecule, could be involved in allergic reactions observed in cow's milk allergic patients exposed to soy-containing foods.

From the full text article:

Food allergy is becoming a medical, economical and social problem. Soybean, together with milk, peanuts and eggs, are the major allergenic foods. This pathology affects the infant population, when the gut barrier is immature and the immune system is still refining its ability to tolerate food proteins. In our country, cow's milk allergy (CMA) constitutes the main food allergy in infancy, but soy allergy has become exacerbated because of the increased utilization of soy-based formulas as cow's milk (CM) substitutes and the inclusion of soy-proteins in many processed foods. Once a food allergy is diagnosed, the only proven therapy is the strict elimination of the offending allergens from the diet. Available substitutes for CM include milks from different mammalian animals, soy-based formulas, hydrolysed cow's milk proteins (CMP) and amino acid-based formulas. Furthermore, there is evidence that soy proteins may trigger allergic reactions in CMA patients, as assessed by a double-blind placebo controlled food challenge (DBPCFC) [1].

Milk contains more than 50 proteins and the major ones are implicated in a number of immunologically mediated reactions [2]. Caseins and β-lactoglobulin (β-Lg) have been described as the main antigenic and allergenic components for human beings [3,4], although immunoglobulins, α-lactalbumin (α-La), and bovine serum albumin (BSA) were also found to be reactive with different isotypes of human antibodies [5,6]. Several immunoreactive epitopes have been identified in caseins [7,8] and β-Lg [9]. Most of the epitopes present in the casein molecules are sequential since the high number of proline and hydrophobic residues (45%) in these proteins determine an undefined secondary and tertiary structure [10]. Besides, caseins tend to aggregate as a result of hydrophobic interactions to give quaternary structures [11], and this may create conformational epitopes buried in the hydrophobic interior of the micelle [7]. These epitopes are only exposed and accessible to the immune system after denaturation of the complex by digestion.

Catefories: 2002, Soy, Dairy, Allergy, Nutrition and diet