IL-15Rα expression by memory CD8 T cells is not required for their proliferation. A mixture of BM from IL-15Rα^-/- (Ly5.1) and wild-type mice (Ly5.1/5.2) was injected into lethally irradiated wild-type mice (Ly5.2). After reconstitution, chimeras were infected with VSV to analyze a viral CD8 T-cell response. (A) The percentage of N-tetramer-positive cells present in the peripheral blood was measured at various times after VSV infection. Wild-type and IL-15Rα^-/- cells were distinguished by the gating on Ly5.1/5.2⁺ and Ly5.1⁺ cells, respectively. Error bars indicate SD. (B) Sixty days after VSV infection, BrdU was added to drinking water for 4 weeks. Lymphocytes from spleens and lungs were isolated and stained with anti-BrdU, N-tetramer, anti-CD8, and anti-Ly5.2. Histograms show BrdU incorporation of N-tetramer-positive CD8⁺ T cells from either Ly5.2+ (wild-type) or Ly5.2^- (IL-15Rα^-/-) cells. Horizontal lines demarcate BrdU-positive cells and the numbers indicate the percentage of BrdU-positive cells.