Cytokine-induced apoptosis of a human LGL leukemia cell line. NK-92 cells were plated at a concentration of 5 × 105/mL in culture medium containing either (A) 15 ng/mL IL-2 alone or (B) IL-2 and 3 ng/mL IL-12 for 24 hours, after which cells underwent cytocentrifuge preparation and Wright-Giemsa staining. Original magnification × 330. (C) NK-92 cells were first cultured at a concentration of 1 × 105 cells/mL for 2 hours in medium containing: 15 ng/mL IL-2; IL-2 and 600 ng/mL doxorubicin; IL-2 and 3 ng/mL IL-12; IL-2, IL-12, and doxorubicin. Cells were next washed three times with RPMI 1640 and plated in a 96-well plate at 10 cells/well in the presence of IL-2 alone or IL-2 and IL-12, as indicated. After 2 days, each well was washed three times with RPMI 1640, and cultures were then continued in medium containing IL-2 for 6 more days. Wells were then visually scored for the presence of a viable colony. Similar results were obtained when IL-15 was substituted for IL-2 in these experiments (data not shown).
