Analysis of proliferation and survival of Tregs during recovery from lymphopenia. (A) Irradiated or nonirradiated mice were injected intraperitoneally with 1 mg of BrdU for consecutive 3 days before sacrifice. Seven days after irradiation, single-cell suspensions were prepared from LNs and were analyzed using FACS. The percentages of BrdU⁺, Ki-67⁺, annexin V⁺, and 7-AAD⁺ cells on gated CD4⁺Foxp3⁺ and CD4⁺Foxp3⁻ subsets are indicated. (B) Forty million of Ly5.1⁺ spleen cells were transferred into irradiated mice. LN cells from day 7 were analyzed by FACS. Histograms show the percentages of BrdU⁺, Ki-67⁺, annexin V⁺, and 7-AAD⁺ cells among Foxp3⁺Ly5.1⁻ recipient cells.