Enhanced Immunological Tolerance against Allograft Rejection by Oral Administration of Allogeneic Antigen Linked to Cholera Toxin B Subunit

A single oral intragastric administration of cholera toxin B subunit (CTB) conjugated to allogeneic thymocytes (ATC, 4 × 107 cells) under conditions allowing the CTB to bind the complex to GM1 ganglioside receptors was shown to be efficacious in inducing peripheral T cell tolerance associated with significant suppression of both primary and secondary accelerated rejection of heart allografts when tested in mice. Allogeneic in vivo delayed-type hypersensitivity (DTH), in vitro cytotoxicity responses, and mixed lymphocyte reactions (MLR) by T cells from mesenteric lymph nodes (MLN), popliteal lymph nodes (PLN), and spleen were significantly reduced in mice treated with the CTB–ATC conjugate, as were also the numbers of cells in these organs producing IL-2, IFN-γ, or IL-4. In contrast, a marked increase in the production of IL-4 in Peyerʹs patches (PP) and of TGF-β1 in PLN was observed. The suppressive potential of T cells from PP and/or MLN after oral treatment with CTB–ATC was further evident by intraperitoneal transfer of such cells from CTB–ATC-treated animals to primed recipients, which led to marked suppression of both allogen-specific DTH and MLR responses. A critical role for PP in inducing peripheral tolerance after oral CTB–ATC treatment was indicated by the absence of tolerance induction in animals whose PP had been destroyed before treatment with CTB–ATC. The results indicate that the protection against allograft rejection by oral treatment with CTB–ATC is mediated by T cells and associated with a strong induction of IL-4 production at mucosal sites and TGF-β1 at the effector sites.