Maintenance of Bcl-2 protein and survival of NK cells cultured with IL-15.

(A) Freshly isolated murine NK cells were stained for baseline (0 hour) expression of Bcl-2 protein by using intracellular flow cytometry and again after culture for 12 and 24 hours with 10 ng/mL IL-15 (shaded area) or medium alone (dark line). NK cells cultured in IL-15 maintained significantly higher mean fluorescence intensity (MFI) of Bcl-2 staining than those cultured in medium alone (158.9 ± 80.4 versus 58.1 ± 17.6; P = .05; n = 4 at 12 hours and 152.4 ± 58.3 versus 28.9 ± 21.0; P = .03; n = 3 at 24 hours). Results are representative of four 12-hour and three 24-hour experiments. (B) Viability of enriched NK cells cultured in the presence of IL-15 (10 ng/mL) for 24 hours was assessed with PI staining. NK cells cultured with IL-15 had 50% less cell death than cells cultured in medium alone (n = 3). Results from one representative experiment are shown.