Increased proliferation of DN3 thymocytes in DKO mice. (A-B) DN thymocytes from wt and CCR7^−/−CCR9^−/− (DKO) mice were stained with antibodies against lineage markers, CD25, CD44, CD117, as well as Ki-67 (A) or DAPI (B). Histograms are electronically gated on DN3 cells (lin⁻CD44⁻CD117⁻CD25⁺). Numbers in histograms indicate frequencies of cells within gates. Graphs indicate percentage of Ki-67⁺ DN3 cells (A) or percentage of cells with DNA content more than 2N (B). Data are from 7 mice per group and represent mean ± SEM. (C) wt and DKO mice were subjected to a 4-hour BrdU pulse. DN thymocytes were stained with antibodies against lineage markers, CD25, CD44, CD117, and BrdU. Plots are electronically gated on DN3 cells. Numbers indicate frequencies of cells within gates. The graph indicates percentage of BrdU⁺ DN3 cells. Data are from 3 mice per group and represent mean ± SEM. *P < .05. ***P < .001.