IL-15 administration increases homeostatic proliferation of CD8⁺ T-cells in syngeneic and allogeneic recipients of CFSE labeled T-cell infusion. (A) Sublethally irradiated B6 (Ly5.1⁺) (SYN) or (B6xC3H)F1 (ALLO) recipients were infused with CFSE-labeled B6-purified T-cells (2 × 10⁷). The recipients received 2.5 μg/d IL-15 or PBS (control) on days 0 to 3. On day 3, splenocytes were harvested and stained with anti-CD8 antibodies for flow cytometric analysis. A representative experiment of 3 is shown. (B) Sublethally irradiated B6 (Ly5.1⁺) or IL-15^-/- recipients were infused with CFSE-labeled B6 (SYN) or B10.BR (ALLO) purified CD8⁺ T-cells (5 × 10⁶). Harvesting, staining, and flow cytometric analysis of splenocytes were as in panel A. The corresponding percentages of the marked regions are shown in each plot.