Heat Denaturation of Egg-White Proteins Abrogates the Induction of Oral Tolerance of Specific Th2 Immune Responses in Mice

Human foods are usually prepared by cooking. Boiling of chicken egg-white (EW) led to decreased allergenicity, and abrogated intestinal uptake of immunoreactive ovalbumin (OVA) when fed to mice. Therefore, the effects of oral administration of boiled EW were examined further in BALB/c mice. Specific IgE, IgG₁ and IgG antibody responses were suppressed by raw EW, but not by EW boiled for 5 or 60 min, fed prior to sensitization with 10  μ g OVA or 1  μ g DNP–OVA in alum. Similar results were obtained when mice were sensitized with 10  μ g conalbumin, ovomucoid or lysozyme in alum. BALB/c spleen cell proliferation and secretion of Th2 cytokines IL-4 and IL-5 during in vitro stimulation with OVA were also suppressed by feeding raw EW, but not by boiled EW. Although heat denaturation of proteins can minimize allergenicity, the present results suggest that over-cooking of proteins may affect their intestinal antigen processing and thus prevent the induction of oral tolerance.