CD8⁺ DCs suppress the MLR, increase IDO production, and retain the capacity to stimulate NKT-cell cytokine secretion. (A) To analyze the in vitro suppression of the proliferation of BALB/c splenic responder CD4⁺ or CD8⁺ T cells in the MLR, responder cells were labeled with CFSE (2.5 × 10⁴ per well), and stimulated with irradiated (3000 rad) C57BL/6 splenic cells (5.0 × 10⁴ per well). Sorted CD8⁺ DCs (2.5 × 10⁴ per well) were or were not added to 5-day cultures. The sorted splenic CD8⁺ DCs were obtained from untreated (n = 9) or TLI-conditioned wild-type mice (n = 8). Representative plots of CFSE staining with percentages of CFSE^lo cells are shown. (B) Mean percentages of CD8⁺ DC suppression of proliferation of CD4⁺ and CD8⁺ T cells are shown. (C) Representative 1-color analyses of intensity of staining for IDO among gated CD8⁺ CD11c⁺ cells are shown. (D) (MFI) of IDO staining of gated CD8⁺ DCs from untreated (n = 9) or Jα18^−/− (n = 5) or TLI-conditioned wild-type (n = 8) or Jα18^−/− (n = 6) mice at day 5 after completion of TLI conditioning is shown. (E) Mean concentrations of IL-4 in supernatants of untreated or TLI-treated splenic CD8⁺ DCs, and untreated NKT cells that were cultured alone or together for 5 days with or without addition of α-GalCer.