(g) Survival determined by annexin V/7-AAD co-staining (unstained cells were considered as viable) of human immune cells (PBMC) cultured for 6 and 12 days in the absence (black bar) or presence (white bars) of various spermidine concentrations (as indicated). Data represent means ± s.e.m. of 3 independent experiments (each performed on PBMC from different donors). *P 0.05 and **P 0.01. 