Expression of Blimp-1 and IL-2. (A) Production of IL-2 by naive CD4⁺ OT2 Blimp-1–sufficient (Ctrl) and –deficient (CKO) cells stimulated with 0.1 μM OVA and APC (determined as described in Materials and methods). Data shown is the percentage of IL-2–producing cells in the live, CD4⁺ cell gate. (B) Steady-state Blimp-1 and IL-2 mRNA (determined by quantitative real-time PCR) in naive WT CD4⁺ T cells stimulated as described in Materials and methods. (C) Few, if any, Blimp-1–expressing cells produce IL-2. Lymph node and spleen cells from Blimp-1-GFP reporter mice were stimulated (top) or restimulated (bottom) and stained for IL-2 and GFP. Plots show GFP and IL-2 in the CD4⁺ cells. Specificity of GFP staining is shown on the top left.