Antigen-specific immunosuppression requires an understanding of the parameters that control peripheral T cell tolerance. A liver-specific inducible promoter was used to drive the expression of the major histocompatibility complex antigen Kb in transgenic mice. Minute amounts of Kb, expressed exclusively on hepatocytes, induced tolerance by partial down-regulation of the T cell receptor (TCR) on the self-reactive CD8+ cells. Contact of these tolerant T cells with high concentrations of Kb after induction led to complete down-regulation of TCR. Thus, tolerant T cells are susceptible to further tolerogenic signals and reach different levels of tolerance depending on antigen dose.