Mediators involved in the inhibitory function of CD11b^hiIa^lo DCs. (A-B) CD11b^hiIa^lo did not induce T-cell anergy (A) and the generation of Treg cells (B). GFP⁺ OVA_323-339 peptide–specific CD4 T cells from (DO11.10 × GFP) F1 GFP⁺mice, stimulated by CD11b^hiIa^lo for 7 days in the presence of OVA_323-339 peptide (GFP⁺CD4), and naive GFP^– OVA_323-339 peptide–specific TCR CD4 T cells from (DO11.10 × GFP) F1 GFP^– mice (GFP^–CD4) were primed with mDCs in the presence of OVA_323-339 peptide. On day 5, the proliferation of GFP^–CD4 T cells and GFP⁺CD4 T cells (A) and the effect of GFP⁺CD4 T cells pretreated by CD11b^hiIa^lo DCs on mDC-induced GFP^–CD4 T-cell proliferation (B) were assayed by FACS. *P > .05. (C) CD4/mDC system was cocultured either with paraformaldehyde-fixed CD11b^hiIa^lo DCs (CD11b^hiIa^lo-fixed) or with 50% CD11b^hiIa^lo DCs culture supernatant (CD11b^hiIa^lo-SN). On day 5, viable peptide-specific CD4 T cells were tested by FACS. *P < .01, **P > .005. (D-E) Anti–IL-10 (5 μg/mL), and anti–TGF-β (5 μg/mL) neutralizing mAbs (D) and 1-methyltryptophan (1 mM), IDO inhibitor, and indomethacin (40 μM), PGE₂ inhibitor (E) were added at the beginning of CD11b^hiIa^lo/mDC/CD4 coculture. On day 5, viable peptide-specific CD4 T cells were tested by FACS. *P > .05. (F-G) The inhibitory function of CD11b^hiIa^lo DCs was NO involved. Serious concentrations of NO donor NOC-18 (F) or serious concentrations of NOS inhibitor PBIT (G) were added into coculture system as indicated. On day 5, viable peptide-specific CD4 T cells were assayed by FACS. *P < .01. Data in panels represent mean ± SD of triplicate samples.