FLT3L-differentiated BMDCs induce proliferation of Tregs. (A) PKH26-labeled lymph node cell suspension from Foxp3EGFP reporter mice was incubated with sorted syngeneic B-cell or syngeneic in vitro FLT3L-differentiated BMDCs for 5 days with or without antagonistic anti-IL-2. Dot plots show PKH26 level on CD4 T cells. (B) PKH26-labeled CD4⁺Foxp3⁺ cells sorted from Foxp3EGFP reporter mice were incubated with or without extra IL-2 and with or without BMDCs. Histograms show PHK26 level on CD4⁺Foxp3⁺ cells after 5 days of incubation. (C) PKH26-labeled CD4⁺Foxp3⁺ cells sorted from Foxp3EGFP reporter mice were incubated with extra IL-2 only (empty histogram) or with BMDCs without (left panel) or with (right panel) cell contact. Histograms show PHK26 level on CD4⁺Foxp3⁺ cells after 5 days of incubation. (D) PKH26-labeled CD4⁺Foxp3⁺ cells sorted from Foxp3EGFP reporter mice were incubated with BMDCs and sorted CD4⁺Foxp3⁻ (CD4:Tregs ratio, 4:1) or CD8⁺ (CD8:Tregs ratio, 2:1) T cells. Cocultures were done in presence or absence of antagonistic anti–IL-2. Histograms show PHK26 level on CD4⁺Foxp3⁺ cells after 5 days of incubation. (E) PKH26-labeled CD4⁺Foxp3⁺ cells sorted from Foxp3EGFP reporter mice were incubated with extra IL-2 only (empty histogram) or with control BMDCs (left panel) or LPS-activated BMDCs (right panel). Histograms show PHK26 level on CD4⁺Foxp3⁺ cells after 5 days of incubation.