IL-15 up-regulates CD44 expression 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 48 hours, the cells were stained for CD4, CD8, and CD44. Expression of CD44 in gated CD8⁺ and CD4⁺ SP thymocytes from 1 of 4 representative animals per group is shown. Histograms of the stimulated cells are shaded gray, and unfilled line histograms represent the unstimulated cells. The bar graph shows the proportion of CD8⁺ cells showing high, intermediate, or low levels of CD44 expression, based on the marker boundaries shown in the histograms.