Effects of IFN-γ, IL-2, and IL-12 on viability of EBV-infected NK leukemia cells. Cells (106/mL) were cultured in the presence or absence of either IFN-γ (10 and 100 U/mL), IL-2 (10 U/mL), or IL-12 (10 ng/mL), and viability of cells was determined on MTT assay 48 hours after the initiation of cultures. Data are shown as percentages of viability determined by OD after the culture/OD before the culture. Numbers in open circles correspond to case numbers in Table 1. (A) The addition of IFN-γ to the culture significantly increased viablity of NK leukemia cells in a dose-dependent manner. The antiapoptotic effects of 1,000 U/mL of IFN-γ did not significantly differ from those of 100 U/mL of IFN-γ (data not shown). Percentages of viability reached more than 100% in some cases cultured with IL-2, which was due to the cell proliferation during the culture with IL-2, whereas IFN-γ did not stimulate proliferation of NK leukemia cells (see text). *A significant difference between the groups (P < .05) determined on Wilcoxon signed-rank tests. (B) The addition of IL-12 inhibited spontaneous apoptosis of NK leukemia cells in only 1 of 4 cases studied. *A significant difference (P < .05) determined on Student’s t-tests.
