Defective T reg cell proliferation in mice lacking MHCII expression pDCs. (A–C) WT:WT and pIII+IV^−/−:WT chimeras were immunized with MOG_35–55+CFA. Nonimmunized (naive) chimeras were used as controls. dLNs were harvested 14 d later and analyzed by flow cytometry. (A) CD25 and Foxp3 expression by CD4⁺ T cells was analyzed. Representative flow cytometry profiles are shown, with percentages of Foxp3⁺ T reg cells indicated. The histogram shows the means and SEM derived from three experiments, each with three mice per group. ns, not significant. (B) Frequencies of proliferating Ki67⁺ cells were determined in the Foxp3⁺ CD4⁺ T reg cell population. Representative flow cytometry profiles are shown, with percentages of Ki67⁺ T reg cells indicated. The Ki67⁺ gate was defined relative to staining with an isotype control. The histogram shows the means and SEM derived from three experiments, each with three mice per group. **, P < 0.01. (C) Frequencies of proliferating Ki67⁺ cells were determined in the CD25⁻Foxp3⁻ (non–T reg cell) CD4⁺ T cell population. Representative flow cytometry profiles are shown, with percentages of Ki67⁺ cells indicated. The Ki67⁺ gate was defined relative to staining with an isotype control. The histogram shows the means and SEM derived from three experiments, each with three mice per group. ns, not significant. (D) IL-10 and TGF-β1 mRNA levels were quantified by quantitative RT-PCR in CD4⁺ T cells purified from the dLNs of WT:WT and pIII+IV^−/−:WT chimeras 14 d after immunization with MOG_35–55+CFA. CD4⁺ T cells purified from LNs of nonimmunized (naive) WT:WT chimeras were used as a reference. The means and SEM were derived from three to four measurements, each made with three mice per group. *, P < 0.05.