IFN-β is required for efficient adaptive immunity against VV in vivo. (A) Maturation of splenic CD11c⁺ DCs. Wild-type 129/Sv (WT) or IFN-αβR^−/− mice were administered 1 × 10⁷ pfu VV intravenously, and splenocytes were harvested 24 hours later, stained with anti-CD11c and anti-CD86 or an isotype control antibody (isotype), and analyzed for CD86 expression by FACS based on isotype control antibody staining on respective CD11c⁺ cells. The percentages of CD11c⁺ DCs expressing CD86 are indicated. (B) VV-specific T-cell activation. Seven days after VV infection, CD5⁺ T cells purified from splenocytes were restimulated with VV at an MOI of 0.5, 0.1, or 0.02 in the presence of corresponding naive irradiated splenocytes. Proliferation of virus-specific T cells was analyzed by ³H-thymidine incorporation. Data reflect the mean plus or minus SD of the stimulation index, calculated by dividing ³H counts in cpm in the presence of viral stimulation by those in the absence of stimulation, as a function of different virus doses. T cells from uninfected 129/Sv mice were used as control (control). (C) Activation of VV-specific effector CD8 T cells. Seven days after infection, splenocytes were stimulated with anti-CD3 and anti-CD28 for 4 hours and assayed for intracellular IFN-γ secretion by CD8 T cells. Events were gated on total lymphocytes. The percentages of IFN-γ–producing CD8 T cells among total lymphocytes are indicated.