Naturally existing tolerogenic DCs suppressed LPS-induced inflammatory responses. (A) The expression of the indicated cell-surface molecules on DCs was analyzed by flow cytometry. Data are represented by a histogram in which cells were stained with the indicated mAb (thick lines) or isotype-matched control Ig (thin lines). The results are representative of 4 experiments with similar results. (B) DCs (5 × 10⁶) were stimulated or not stimulated with LPS (1 μg/mL) for 24 hours, and the culture supernatants were analyzed for production of TNF-α (left panel) and IL-10 (right panel). ^*P < .01 compared with splenic CD11c^lowCD45RB^high DCs; †, compared with in vitro-generated CD11c^lowCD45RB^high DCs by Student paired t test. (C, D) D-GalN-sensitized mice (5 animals/group) were given intraperitoneal injections of LPS (1 μg/mouse) 2 hours after the intraperitoneal injection of splenic CD11c^lowCD45RB^high DCs, in vitro-generated CD11c^lowCD45RB^high DCs, pDC_regs, or DC_regs (10⁶/mouse). (C) Sera were collected 2 hours after LPS challenge and were analyzed for cytokine production. Data were expressed as mean ± SD of duplicate samples, and the results are representative of 2 experiments with similar results. ^*P < .01 compared with untreated control; †, compared with splenic CD11c^lowCD45RB^high DCs; ‡, compared with in vitro-generated CD11c^lowCD45RB^high DCs, by Student paired t test. (D) Survival was monitored at the indicated times, and the results are representative of 2 experiments with similar results. ^*P < .01 compared with untreated mice; †, compared with mice given injections of splenic CD11c^lowCD45RB^high DCs; ‡, compared with mice given injections of in vitro-generated CD11c^lowCD45RB^high DCs; §, compared with mice given injections of pDC_regs, by the log-rank test.