Induction of the senescence-like phenotype in APDCs and PSFCs after irradiation. (a) A typical example of senescence-like cells. (b) Quantitative analysis of the induction of the senescence-like phenotype in APDCs and PSFCs after irradiation. For quantitative analysis, senescence-associated -β-galactosidase-positive and enlarged cells were considered to be senescent cells. The percentages of senescent cells three days after 4 Gy of irradiation were determined in APDCs and PSFCs. At least 200 cells were counted in each group. Results are expressed as means ± SE of three independent samples. *, P < 0.05. Scale: 100 μm.