IL-15 promotes growth of SD-1 cells under low-serum conditions, which is independent of apoptosis. (A) SD-1 cells were grown in RPMI media without addition of fetal calf serum, with (dashed line) or without (solid line) 25 ng/mL IL-15. The growth curve from 1 representative experiment of 3 is shown. (B) SD-1 cells were grown in RPMI supplemented with increasing concentrations of fetal calf serum with (black bars) or without (white bars) 25 ng/mL of IL-15. The total number of viable cells in each group at 72 hours is shown. Data represent mean ± standard error of the mean from 3 independent experiments. Data were analyzed by a Mann-Whitney U test. *P < .05, **P < .01, ***P < .001. (C) Percentage increase in cell counts of IL-15–treated SD-1 (dark bars) and Sup-B15 (light bars) compared with media control. Data represent mean ± standard error of the mean from 3 independent experiments. SD-1 data are from the same experiments as in panel B above, represented in a different format. (D) PARP cleavage analysis of SD-1 cells exposed to increasing concentrations of serum ±25 ng/mL IL-15 for 96 hours. The positive-control lane represents SD-1 cells exposed to the apoptosis-inducing agent AA2 (50 μM) for 1 hour. Histone H3 was used as a loading control. FCS, fetal calf serum.