RESUMO
BACKGROUND: Oral administration of allergens can induce immune tolerance to specific allergens in rodents and hence might be a possibility to prevent and treat allergic diseases in human subjects. However, the gastrointestinal tract of mice is different from that of human subjects. The absorption of specific antigens and subsequent antigen presentation to intestinal T cells is different in both species, making it difficult to extrapolate results. OBJECTIVE: We investigated primary oral tolerance to ovalbumin (OVA) in an IgE high-responder dog model, which is more predictive for human allergic diseases than corresponding rodent models. METHODS: Oral tolerance was induced by means of a 28-day treatment with OVA dissolved in cow's milk. RESULTS: We observed reduced OVA-specific IgE and IgG production in response to ensuing subcutaneous challenges. Allergic conjunctivitis induced by means of ocular and airway provocation was significantly reduced in tolerized animals compared with that seen in nontolerized control animals. In addition, eosinophilia and neutrophilia in bronchoalveolar lavage fluid and bronchoconstriction after airway allergen challenge were significantly suppressed in tolerized animals. Cytokine analysis by means of real-time PCR on bronchoalveloar fluid cells after allergen challenge revealed a high-level expression of IL-10 and transforming growth factor beta, predominantly in the CD14(+) population. CONCLUSION: Feeding infant beagles with OVA for 4 weeks is sufficient to prevent hallmark manifestations of asthma and allergy in adult life. The mechanism of oral tolerance involved an increased expression of IL-10 and transforming growth factor beta cytokines.