Nutritional Status Enhancing Oral Tolerance against Dietary Antigens and its Physiological Mechanisms

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Using animal model for oral tolerance against ovlbumin(OA), we investigated the effects of dietary proteins on the oral tolerance system. Female BALB/c mice were fed either 20% or 5% protein diet with oral administration of OA before intraperitoneal immunization of this protein(tolerated group), Sensitized mice were prepared by the same manner as above except for orally administration of distilled water(sensitized group). Sensitization of OA elevated total IgE and induced the production of OA specificantibodies(IgE,IgG,IgG1 and IgG2a) in serum in both mice fed 20% and 5% protein diet. Total IgE and OA specific IgE in the sensitized group were higher in mice fed 20% protein diet than in those fed 5% protein diet. When mice were immunized with OA after oral administration of this protein, total IgE and OA specific antibodies including IgE,IgG,IgG1 and IgG2a were significantly reduced in mice fed 5% protein diet but almost not effected in mice fed 20% protein diet. IL-4 was produced in spleen cell culture supernatants in the sensitized and tolerated groups in mice fed 20% and 5% protein diet. The amount of the production of the cytokine in the tolerated group of mice fed 5% protein diet was significantly lower than in the sensitized and tolerated group of mice fed 20% protein diet. The constant production of IFN-γ from spleen cells was almost disappeared in the sensitized and tolerated group in mice fed both 20% and 5% protein diet. These findings suggested that low protein diet prefer to introduce oral tolerance against dietary antigens, which might be attributed by down-regulation of Th2 cytokines in low protein diet.