Reduced proliferation in

PU.1^−/− NK cells. (A) Blood cells were isolated from chimeras 4 weeks after the transfer of FL-HSCs. The figure indicates the mean and standard deviation of cycling NK cells in 6 WT and 6 PU.1^−/− chimeras; *P = .008. (B) Freshly sorted NK cells from spleen of chimeras were plated at 2 × 10⁴ cells/well and expanded in IL-2 for 7 days, and thereafter counted. (C) The same cells were replated at 10⁵ cells/well and further stimulated with IL-12 overnight. For detection of apoptotic and proliferating NK cells, cells were stained with mAbs specific for NK1.1-PE and further stained with 7-AAD to reveal the DNA content. Proliferating cells (in G2/M) contain more DNA, whereas cells dying by apoptosis are hypodiploid.