Proliferation pattern of cytokine-stimulated lymphocytes. (a) Resting peripheral blood lymphocytes (PBLs) undergo cell divisions when they are stimulated with cytokines over 8 days. Freshly elutriated lymphocytes were labeled with 5 μmol/l carboxyfluoroscein succinimidyl ester (CFSE) and stimulated with IL-2, IL-6 and tumour necrosis factor-α for 8 days. The number of cell divisions was analysed on day 8 using CellQuest software. Markers (M1 to M7) indicate sequential cell divisions. (b-e) Proliferation of subpopulations of PBLs stimulated with cytokines. CFSE-labelled PBLs were counterstained with antibodies to CD3 (panel b), CD4 (panel c), CD8 (panel d) and CD56 (panel e). On day 8 the number of cell divisions for each subpopulation of PBLs was acquired and analyzed using CellQuest software. Results for all figures are shown from one donor representative of seven different experiments.