pDCs promote the selective expansion of natural T reg cells. (A and B) BM pDCs (CD11c^intB220⁺PDCA-1⁺) or BM cDCs (CD11c^hiB220⁻PDCA-1⁻) were isolated from WT mice, loaded with MOG_35–55 and activated with CpG-A plus CpG-B or LPS, respectively. The DCs were then used to stimulate CD4⁺ T cells isolated from 2D2 × Foxp3-GFP mice. (A) The frequencies of GFP⁺ T reg cells were analyzed in the CD4⁺ T cell population after 96 h of stimulation. Representative flow cytometry profiles are shown, with percentages of GFP⁺ T reg cells indicated. The histogram shows the percentages of GFP⁺ T reg cells in the CD4⁺ 2D2 T cell population. The means and SEM were derived from three experiments. ***, P < 0.001. (B) Concentrations of IFN-γ and IL-17 were measured in the culture supernatants. The histogram shows the means and SEM derived from three experiments. *, P < 0.05. (C) Total or GFP⁻ CD4⁺ T cells were purified from 2D2 × Foxp3-GFP CD45.2⁺ donors (left profiles) and transferred into CD45.1 hosts. The recipient mice were immunized 1 d after the transfer with MOG_35–55+CFA. dLN cells isolated 6 d after the transfer were analyzed by flow cytometry for the frequency of CD45.2⁺ 2D2 cells in the total CD4⁺ T cell population (middle profiles) and for GFP expression in CD4⁺CD45.2⁺ 2D2 T cells (right profiles). Zoomed views are shown in the right profiles to facilitate visualization of the minor GFP⁺ T reg cell populations. The results are representative of two experiments. The means and SEM were derived from three mice per group. *, P < 0.05. (D) Total or GFP⁻ CD4⁺ T cells were purified from Foxp3-GFP CD45.2⁺ donors (left profiles) and transferred into CD45.1 hosts. The recipient mice were immunized 1 d after the transfer with MOG_35–55+CFA. dLN cells isolated 6 d after the transfer were analyzed by flow cytometry for the frequency of CD45.2⁺ donor cells in the total CD4⁺ T cell population (middle profiles) and for GFP expression in the donor CD4⁺CD45.2⁺ T cells (right profiles). Zoomed views are shown in the right profiles to facilitate visualization of the minor GFP⁺ T reg cell populations. The results are representative of two experiments. The means and SEM were derived from three mice per group. ***, P < 0.001.