IL-15 rescues PBLs from apoptosis. (A) Altered pool sizes of nonblastic, blastic, and apoptotic cells in lymphocytes populations. PBLs triggered or not with anti-CD3 mAbs were incubated for 10 to 15 days in the absence or presence of increasing concentrations of IL-15 or 100 IU/mL of IL-2. Shown are typical forward-scatter (size) versus side-scatter (granularity) profiles of cells gated on the indicated populations. Apoptotic cells (Ap) are defined by their small size and high granularity. Viable cells in cultures included nonblastic cells (NB) and distinctly larger blastic cells (Bl), the latter being absent in cultures incubated without exogenous cytokines. (B) Bars represent the percentage of nonapoptotic cells, defined by the ratio between Ap pool and NB + Bl pools. Each bar represents mean of 3 different donors (IM06, IM07, and IM01 vs HS03, HS06, and HS11) in the different culture conditions. P values (< .005) between different conditions culture were calculated with Student t test.