We immunized AKR/n (H-2k) spleen cells in BALB/c (H-2d) mice via the portal vein (pv) and investigated the role of hepatic mononuclear cells (MNC) in the induction of alloantigen-specific immune tolerance. MNC in the liver and spleen of pv-administered mice were demonstrated to abrogate the responses to AKR/n alloantigens in allogeneic MLR. On the contrary, MNC in the liver and spleen of mice administered subcutaneously with the same antigens showed greater responses than those of control mice. The tolerance induced by pv administration was alloantigen-specific and appeared earlier in hepatic MNC than in splenic MNC. Furthermore, hepatic MNC of pv-administered mice had a suppressive effect when these cells were added to allogeneic MLR, in which mitomycin C (MMC)-treated AKR/n splenic MNC were used as stimulator and control BALB/c splenic MNC were used as responder. Splenic MNC of pv-administered mice and hepatic MNC of control mice did not show such suppressive effects. Such suppression was alloantigen-specific, since no suppression was induced when hepatic MNC of pv-administered mice were added to a system using MMC-treated C57BL/6 (H-2b) splenic MNC. The alloantigen-specific suppression induced by hepatic MNC was abrogated by a depletion of TcR-αβ+ cells but not of CD4+, CD8+, nor B220+ cells from hepatic MNC. These results suggested that alloantigen-specific suppressor cells appeared predominantly in the hepatic MNC of pv-administered mice and displayed the phenotype of TcR-αβ+CD4-8- double-negative T cells, although alloantigen-specific tolerance was induced in both hepatic and splenic MNC.
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