Figure 5. The impact of age on stem cell numbers. S/P cells were assessed in HMEC strains based on flow cytometry assessment of ALDH+ signal. The fraction of ALDH+ cells relative to the unexposed control was plotted against age of the individual the strain was derived. Data are based on two independent experiments for high and low dose. Roughly equitoxic doses of Cs and Ti were used for exposures (LD-CS = 0.12 Gy; HD-CS = 0.8 Gy; LD-Ti = 0.05 Gy; HD-Ti = 0.5 Gy). Blue and red symbols represent strains exposed to Cs and Ti ion respectively. Empty circles represent low dose and solid circles high dose exposures. Dotted and solid lines represent the regression lines and note the relationship of stem cell numbers with age for each radiation type.