Lansdorp Figure 4 (in Verfaillie et al). Telomere length analysis in subpopulation of human nucleated blood cells using flow fluorescence in situ hybridization (FISH; Baerlocher and Lansdorp, unpublished).

For this type of analysis, nucleated blood cells following red cell lysis are hybridized with fluorescently labeled telomere probe together with fixed cow thymocytes (with long telomeres: vertical bars, left panels) as internal controls. Following wash steps to remove unlabeled probe and incubation with labeled antibodies (e.g., phycoerythrin-labeled anti-CD20, right panels) the cells are analyzed by flow cytometry. Note the decline in telomere fluorescence (on a linear scale) with age in both granulocytes (with high side scatter, left panels) and lymphocytes (low side scatter, increased heterogeneity with age, left panels) and the presence of some CD20⁺ B cells with very long telomeres in the 90-year-old normal donor.