LRDCs inhibit antigen-specific CD4 T-cell proliferation both in vitro and in vivo. (A,C) CD4 T cells from DO11.10 × C57BL/6 F1 hybrid mice were cocultured with cDCs and/or LRDCs in the presence of OVA_323-339 peptide, or CD4 T cells were cocultured with OVA_323-339 peptide–loaded cDCs (OVA-cDC) in the presence or absence of OVA_323-339 peptide–loaded LRDCs (OVA-LRDC) or control peptide LCMV-NP_309-328–loaded LRDCs (LCMV-LRDC). After 5 days, the total number of live CD4 T cells was counted by FACS (A), and the cytokine release was detected by ELISA (C). *P < .001; ***P > .05. (B) CD4 T cells labeled with 5 μM CFSE were cocultured with cDCs and/or LRDCs in the presence of OVA_323–339 peptide; the dilution of CFSE was then assayed by FACS. (D) CD4 T cells from DO11.10 × C57BL/6 F1 hybrid mice were labeled with 5 μM CFSE and then transferred intraperitoneally into BALB/c × C57BL/6 F1 hybrid mice; 24 hours later, antigen-loaded cDCs and/or LRDCs were also transferred into abdominal cavity. After 4 days, mononuclear suspensions from spleen, lymph nodes, and the liver were assayed for CFSE dilutions by flow cytometry. Numbers in bottom right indicate the percentages of proliferated CD4 T cells. Data are presented as mean plus or minus SD of triplicate samples. Data in panels A and C were pooled from 4 experiments. Data in panels B and D are representative of 3 independent experiments.