DN T cells are anergic upon restimulation by mDCs and are potent in suppressing same-alloantigen–triggered naive CD4⁺CD25⁻ T-cell proliferation. (A) DN T cells and CD4⁺ T cells isolated from primary MLRs stimulated by DBA/2 mDCs plus IL-15 were restimulated by mature DBA/2 DCs plus the indicated cytokines for 4 days. Proliferation was determined by [³H] TdR incorporation and shown as means of 3 independent experiments. Error bars represent standard deviation. (B) DN T cells retain the DN phenotype 4 days after restimulation with mDCs with or without IL-2 or IL-15. (C) C57BL/6 DN T cells induced by mature DBA/2 DCs potently suppress CFSE-labeled C57BL/6 (CD45.1) CD4⁺CD25⁻ T-cell proliferation triggered by the same alloantigens (mature DBA/2 DCs). The horizontal bars gate the nondividing cells, and the numbers refer to the percentages of these cells. (D) C57BL/6 DN T cells induced by mature DBA/2 DCs suppress CFSE-labeled C57BL/6 (CD45.1) CD4⁺CD25⁻ T-cell proliferation triggered by third party alloantigens (mature C3H DCs) at lower efficacy.