Defective repopulation of total T cells as well as CD4 and CD8 subpopulations in irradiated Rsk2 KO mice and activation of Rsk2 by anti-CD3 plus anti-CD28 and IL-15 in mouse T cells but not by IL-7. WT and Rsk2 KO mice were sublethally irradiated and the cellularities of total splenocytes (A) and indicated subpopulation of cells (B-I) from these mice were determined 16 days after irradiation. A nonirradiated WT mouse was used as the control. Shown are means plus or minus SEM (n = 5).