Effect of CY on in vivo proliferation of CD4⁺25⁺ and CD4⁺25^- cells. Mice were injected intraperitoneally with 2 mg CY. Control mice received no CY. Treated and control mice were given BrdU water beginning at the time of injection. Mice were killed at either 24 or 48 hours, cell surface marker staining was performed on spleen and LN cells, and cells were stained for BrdU incorporation. (A-H) BrdU incorporation by CD4⁺25⁺ cells. (A) Spleen cells from control mice at 24 hours after CY administration. (B) LN cells from control mice at 24 hours after CY administration. (C) Spleen cells from control mice at 48 hours after CY administration. (D) LN cells from control mice at 48 hours after CY administration. (E) Spleen cells from CY-treated mice at 24 hours after CY administration. (F) LN cells from CY-treated mice at 24 hours after CY administration. (G) Spleen cells from CY-treated mice at 48 hours after CY administration. (H) LN cells from CY-treated mice at 48 hours after CY administration. (I-J) BrdU incorporation by CD4⁺25^- cells. (I) LN cells from control mice after 48 hours. (J) Spleen cells from control mice after 48 hours. Percentages indicate the percent of BrdU⁺ cells. Horizontal bars are gates indicating what percent of cells are positive for BrdU⁺ cells.