Splenic dendritic cells induced by oral antigen administration are important for the transfer of oral tolerance in an experimental model of asthma.

Peripheral tolerance can be induced after the feeding of Ag, which is referred to as oral tolerance. We demonstrated in this study that the oral administration of OVA induced tolerance in an experimental model of asthma in mice, and investigated which cells function as the regulatory cells in the transfer of this oral tolerance. In OVA-fed mice, the percentage of eosinophils in bronchoalveolar lavage fluid, serum IgE levels, airway hyperresponsiveness, and mRNA levels of IL-13 and eotaxin were significantly lower than found in nonfed mice. Histological examination of lung tissue showed a suppression of the accumulation of inflammatory cells in the peribronchial area of OVA-fed mice. Feeding after the first immunization or between the first and the second immunization suppressed these findings, whereas feeding just before the airway Ag challenge did not. The suppression of disease in OVA-fed mice was successfully transferred by injection of whole spleen cells of OVA-fed mice. When CD11c+ dendritic cells (DCs) were removed from splenocytes, this transfer of suppression was completely abolished. The injection of splenic DCs purified from OVA-fed mice alone transferred the suppression, whereas the injection of splenic DCs from naive mice that were cocultured with OVA in vitro did not. These data suggest that not only CD4+ T cells, but also CD11c+ DCs induced by Ag feeding are important for the active transfer of oral tolerance in this murine experimental model of asthma.