T_reg cells expanded in RelB^−/− BMCs are not responsible for the reduced effector T-cell expansion. Cohorts of irradiated WT and RelB^−/− BMCs were transplanted with BM from PC61-treated Balb/c donors in combination with LN T cells from control or PC61-treated Balb/c donors. (A) Efficacy of donor T_reg depletion was examined in LN cells from control mAb or PC61-treated Balb/c donors using 3-color flow cytometry with CD25-FITC, CD4-PE, and FoxpP3-Alexa647 mAbs (numbers represent proportion of LN cells in that quadrant). (B) Donor splenic CD4⁺ T_reg (CD3⁺H2D^d-posCD4⁺FoxP3⁺) numbers and proportions within CD4⁺ compartment, and (C) effector CD4⁺ T cells (CD3⁺H2D^d-posCD4⁺FoxP3⁻) were quantitated, and (D) serum IFNγ and IL-5 levels were determined in allogeneic BMC transplant recipients 10 days after BMT. *P = .016, BMC transplant recipients: WT (■, n = 5) or RelB^−/− (□, n = 4). Results represent mean ± SEM of individual animals.