Normal Regulatory α/β T Cells Effectively Eliminate Abnormally Activated T Cells Lacking the Interleukin 2 Receptor β in Vivo

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Abstract
Although interleukin 2 (IL-2) has been thought to be the most important cytokine for T cell growth, animals lacking IL-2 or a component of its receptor molecules have more expanded T cells with activated memory phenotype, indicating an indispensable role for the IL-2/IL-2 receptor system in regulating the size and activity of the T cell population. In this study, we investigated the possible mechanism of abnormal expansion of activated T cells in IL-2 receptor β chain (IL-2Rβ)−/− mice using the systems of bone marrow transplantation and T cell transfer. Here, we show that IL-2Rβ2/− T cells in mice reconstituted with a mixture of IL-2Rβ2/− and IL-2Rβ1/+ bone marrow cells did not develop into an abnormally activated stage, and that already activated IL-2Rβ2/− T cells were effectively eliminated by IL-2Rβ1/+ T cells when both cells were cotransferred to T cell–deficient host mice. This regulation and/or elimination was dependent on T cells bearing α/β type T cell receptor, especially on CD8+ T cells and independent of the Fas–Fas ligand (FasL) system. IL-2Rβ1/+ T cells that eliminated activated IL-2Rβ2/− T cells expressed FasL, perforin, granzyme B, and tumor necrosis factor α/β. These results indicate a novel function of IL-2Rβ that is necessary for the induction of regulatory T cells acting to eliminate activated T cells.