Failure to Induce Oral Tolerance in Mice Is Predictive of Dietary Allergenic Potency among Foods with Sensitizing Capacity

Abstract

Animal models are needed to assess novel proteins produced through biotechnology for potential dietary allergenicity. Currently proposed rodent models evaluate sensitizing potential of food extracts or proteins following parenteral administration or oral administration with adjuvant. However, food allergy requires not only the potential to induce immunoglobulin (Ig) E but also the capacity to avoid induction of oral tolerance (specific inhibition of IgE production). Here we describe a mouse model that assesses the potential of food extracts to induce oral tolerance. Adult C3H/HeJ mice were exposed orally to food extracts (without adjuvant) and subsequently challenged with the extract ip. Reduction of antigen-specific serum IgE relative to appropriate controls was used to indicate tolerance. Foods associated with persistent, severe allergy (peanut, Brazil nut), and nonallergens (turkey, spinach) were less tolerizing than foods associated with frequently resolving allergy (egg white). Digestibility was assessed in vitro, and pH alterations or encapsulation were used to modify solubility or digestibility. Egg white, peanut, and Brazil nut proteins were resistant to gastric enzyme (pepsin) degradation; turkey and spinach were not. Among pepsin-resistant proteins, peanut and Brazil nut appeared more sensitive to intestinal enzyme than egg white. For the extracts tested, full gastric digestion appeared to prevent induction of tolerance. Once through the stomach, only proteins resistant to intestinal enzymes induced tolerance. Limiting gastric digestion with sodium bicarbonate enhanced tolerance to peanut and Brazil nut. This model represents a complementary method of assessing potential allergenicity. Also, the conditions under which the test protein is encountered may impact experimental outcome.