IL-15 and IL-7 up-regulate Bcl-xL expression selectively in SOCS1-deficient CD8⁺ SP thymocytes. Total thymocytes from SOCS1^-/-IFNγ^-/- and control mice were stimulated with 40 ng mL^-1 IL-15 or a 1:20 dilution of IL-7-containing CS. After 36 hours, the cells were stained for CD4 and CD8, fixed, and stained for intracellular Bcl-2 or Bcl-xL. Expression of Bcl-2 or Bcl-xL in gated CD8⁺ and CD4⁺ SP thymocytes from a representative of several experiments is shown. Histograms of the stimulated cells are shaded gray, and unfilled line histograms represent the unstimulated cells.