Loss of Blimp1 alters NK-cell maturation and homeostasis. (A) Rag1^−/−Ly5.1 mice were lethally irradiated and reconstituted with E14.5 fetal liver cells of the indicated genotypes. Donor derived (Ly5.2⁺) cells from the spleen and bone marrow of these mice were analyzed 6-8 weeks after reconstitution for the indicated markers. Numbers are the mean ± SEM for 4-6 mice. (B-C) Lethally irradiated Rag2^−/−γc^−/− mice were reconstituted with E14.5 Rag2^−/−Blimp1^+/+ or Rag2^−/−Blimp1^gfp/gfp fetal liver cells. After reconstitution, NK cells (NK1.1⁺CD49b⁺) in the spleen or bone-marrow cells were analyzed for the markers as indicated. Open histograms, Rag2^−/−Blimp1^+/+; filled histograms, Rag2^−/−Blimp1^gfp/gfp. Numbers in the plots show the proportion of NK cells in each quadrant. Results are representative of at least 3 experiments each containing 3-4 mice. (D) Bone marrow chimeras were generated by reconstitution of lethally irradiated C57BL/6 Ly5.1⁺ mice with a 1:1 mixture of Ly5.1⁺ and Blimp1^gfp/gfp (Ly5.2⁺) bone marrow and analyzed after 10-12 weeks. The ratio of Ly5.1⁺ NK cells and Ly5.2⁺Blimp1^gfp/gfp NK cells in different organs is shown as the mean ± SEM (n = 6-9). P value compares the indicated values to zero: *P = .03; **P = .007; ***P < .00001 (E) Marker expression on Ly5.2⁺Blimp1^gfp/gfp (filled histogram) or Ly5.1⁺ wild-type NK cells (open histogram) in mixed bone-marrow chimeras.