Detection of transferred NK cells in IL-15^−/− and control mice.

CFSE⁺ NK cells were assessed by flow cytometry 1.5 and 5 days after transfer into IL-15^−/− and control (IL-15^+/−) mice. (A) The spleen (SP), blood (BL), and liver (LV) were analyzed for the presence of CFSE⁺DX5⁺ NK cells. Cells were gated on viable lymphocytes. Transferred cells are highlighted in boxes, and the percentages for each organ are shown. At day 1.5, transferred cells were detectable in both IL-15^−/− and control mice, with significantly higher numbers of NK cells recovered from the controls (7.4 ± 0.7 fold; P < .003; total NK cells). At day 5, transferred NK cells were undetectable in IL-15^−/− mice but still present in control mice. Results are representative of 4 independent experiments at 1.5 days and 4 independent experiments at 5 days. (B) For 3 of the 1.5-day and 5-day adoptive transfer experiments, NK cells were isolated from Ly5.1⁺ mice, labeled with CFSE, and transferred into IL-15^−/− and control mice (both of which are Ly5.2⁺). Consistent with the results shown in panel A, transferred cells could be detected as CFSE⁺Ly5.1-PE⁺ in the spleens of IL-15^−/− and control mice killed at day 1.5 but were undetectable in IL-15^−/− mice at day 5.