CD8+ CD45RA+CD28+ T-cells from 5 young (<35 years of age) and 5 elderly (>65 years of age) donors. A) Expression of CD surface markers by fluorescent-activated cell sorting (FACS) analysis . Numbers in the graph indicate the percentage of cells in the respective quadrant. Ten identical experiments were performed. B) Flow fluorescent in situ hybridisation (FISH) analysis of the relative telomere length . Filled black peak represents the tetraploid human T-cell leukemia cell line 1301 with a known telomere length of 25 kbp (internal standard). The figure shows one of ten identical experiments.