Animal models which reflect the induction and development of food-allergic reactions are important in the identification of allergenic potential of food proteins and peptides. A number of rat strains, including PVG, Hooded Lister and Brown Norway have been shown to produce immunoglobulin (Ig) E antibodies to food proteins as well as to inhaled allergens. Previous work in our laboratory using the Brown Norway (BN) rat has shown that specific IgE is produced following administration of ovalbumin and milk products via both enteral and parenteral route; this has allowed us to rank ovalbumin, lactoferrin and bovine serum albumin in terms of their inherent allergenic potential and has enabled us to demonstrate that milk protein allergens recognized by the systemically-sensitized animal are consistent with those recognized by sera from cow's milk-allergic patients (the most common allergens recognized were β-lactoglobulin and the α, β and κ-caseins).
To demonstrate that the BN rat model can be used to identify the major IgE-binding peptides from β-lactoglobulin, a known human food allergen, and that those IgE-binding peptides are similar to those recently identified using sera from cow's milk-allergic patients.
BN rats were exposed to β-lactoglobulin or to semiskimmed milk via the intraperitoneal route in the presence of the adjuvant carrageenan. Specific IgE raised against β-lactoglobulin was determined by a direct enzyme immunoassay using acetyl-cholinesterase substrate; specific IgG responses were also monitored. Overlapping synthetic peptides and tryptic peptides were used within the ELISA to identify the major and minor IgE-binding immunoreactive sequences.
In terms of comparative immunogenicity, there appeared to be sequences that were predominantly IgE- or IgG-reactive. IgE-dominant regions were amino acid sequences 21–40, 41–60, 107–117 and 148–168 whereas sequences 1–24, 67–77, 82–92, 85–95 and 117–127 appeared more selective for IgG antibody recognition. An increased capacity to induce specific IgE was observed when the allergen was present in the context of whole food.
These studies provide evidence that the immune system of the BN rat and humans — at least in the case of milk allergens — is recognizing similar protein allergens and indeed, at the molecular level, similar peptide epitopes.