Blimp1 expression in NK cells is independent of IRF4 and Bcl6. (A) DX5⁺ NK cells were expanded in IL-15 for 5 days and then transferred into cytokines for 2 days as indicated. Protein extracts were subjected to Western blotting with antibodies to the indicated proteins. (B) Blimp1^gfp/+ mice were bred on Irf4^−/− or Bcl6^−/− backgrounds and TCRβ⁻NK1.1⁺CD49b⁺ NK cells were analyzed for Blimp1/GFP expression (empty histogram, wild-type control; filled black histogram, Blimp1^gfp/+; filled gray histogram, Blimp1^gfp/+ and deficient for the indicated transcription factor). (C) Flow cytometric analysis of splenocytes isolated from Irf4^−/−, Bcl6^−/−, or control mice (top panel). Gated TCRβ⁻NK1.1⁺CD49b⁺ NK cells are shown in the lower panel. Numbers indicate the proportion of cells of the indicated phenotype. The results shown are representative of 3-6 independent experiments.