Changes in the percentages and mean content of perforin (MFI) in subpopulations of perforin positive PBL (CD8⁺P⁺ and CD56⁺P⁺) cultured for 6 or 24 hours in high IL-2 medium. Results are expressed as mean values, and each point is the average value of five to six samples. Perforin positive cells: adults, ○; elderly persons, □. MFI: adults, •; elderly persons, ▪.