Immunohistochemical detection of protein adducts of 2,4-dinitrochlorobenzene in antigen presenting cells and lymphocytes after oral administration to mice: lack of a role of Kupffer cells in oral tolerance.

Although current studies suggest that most drug-induced allergic reactions (DIARS) are caused by immunogenic conjugates formed from the reaction of a reactive metabolite of a drug with cellular proteins, it is not clear why these reactions are relatively rare. One possible pathway that may explain the low incidence of DIARS in many cases is oral tolerance, an antigen-specific immunological hyporesponsiveness induced by oral administration of antigens. The mechanism of oral tolerance, however, is not clearly understood and is difficult to study directly with drugs, because animal models of DIARS have been elusive. We chose 2,4-dinitrochlorobenzene (DNCB) as a model compound to circumvent this problem because animal models of allergic reactions have been established for this compound. DNCB forms immunogenic 2,4-dinitrophenylated (DNP) protein conjugates that can induce immune reactions and it causes oral tolerance when it is fed to animals prior to sensitization. We hypothesized that DNP-protein conjugates may have a role in oral tolerance. To test this idea, we have begun to identify cells bearing these conjugates after the oral administration of DNCB. Female C57BL/6J mice were fed DNCB and tissues were examined after 6 and 24 h. Immunohistochemical analysis indicated the presence of DNP-protein conjugates in enterocytes of the small intestine, in macrophages and lymphocytes of the mesenteric lymph nodes, in dendritic cells and lymphocytes of the spleen, and in Kupffer cells and other sinusoidal cells of the liver. It was found that Kupffer cell depletion did not affect oral tolerance to DNCB. The findings suggest that the cells bearing DNP-protein conjugates, other than Kupffer cells, in the liver and other tissues may be important in the induction of oral tolerance against DNCB. Protein adducts of drugs administered orally may also be present in these cells, and they may have a role in the downregulation of DIARS in many individuals.