In vivo administration of IL-2 or IL-15 could not rescue defective homeostatic proliferation in Rsk2 KO mice, and Rsk2 mice had normal expression of IL-2, IL-7, and IL-15 in spleen and bone marrow cells. (A-C) Sublethally irradiated WT and Rsk2 KO (KO) mice were intraperitoneally injected daily for 15 days with either 10 μg of IL-2 or IL-15 in 0.2 mL PBS, or 0.2 mL PBS as control, and the cellularities of total T cells (A) and the CD4⁺ (B) and CD8⁺ (C) subpopulations from these mice were determined. (D-F) Ex vivo mRNA expression of IL-2 (D), IL-15 (E), and IL-7 (F) in splenocytes (Sp) and bone marrow (BM) from WT and Rsk2 KO (KO) mice was determined by RT-PCR, and the expression levels were shown as relative to the levels from splenocytes of WT mice.