IL-15Rα expression by BM-derived cells mediates memory CD8 T-cell proliferation. Spleen cells from VSV-infected B6 mice were enriched for CD8 T cells, labeled with CFSE, and transferred to various BM chimeras (10 × 10⁶ CD8 T cells/mouse). Forty days after transfer, lymphocytes from spleen (SP) and lung (LG) were analyzed for CFSE intensity, N-tetramer reactivity, and CD8 and CD44 expression. (A) Histograms showing intensity of CFSE on N-tetramer-positive CD8⁺ T cells and CD44^hiCD8⁺ T cells. R indicates the percent of cells that responded. (B) Comparison of the amount of tetramer-positive CD8⁺ T cells recovered from the spleen and the lung from each group of BM chimeras. Control chimeras are represented by the Wt → Wt. Error bars indicate SD (P < .05).