DN and CD11b^low NK cells display a high rate of proliferation. NDE mice were injected with phosphate-buffered saline (A) or DT (B) and injected with BrdU 7 days later. Six hours after BrdU injection, BrdU incorporation was measured in bone marrow NK-cell subsets by flow cytometry, as described in “Measurement of BrdU incorporation.” Results show the mean ± SD BrdU incorporation in each NK-cell subset; n = 3 experiments. Statistical comparisons between groups were performed using Mann-Whitney tests: *P < .05, ***P < .001.