Figure 5: Detection of apoptosis in fibroblasts by flow cytometry. (a) Most of the fibroblasts in the SIG were alive, with only 2.8% of apoptotic cells. (b) The high-dose UVA irradiation (86.4 J/cm2) strongly induced cellular apoptosis in cultured fibroblasts, with 61.6% apoptotic cells. (c and d) Preirradiation of low-dose UVA reduced cellular apoptosis induced by the subsequent lethal dose of UVA irradiation. Irradiation with 86.4 J/cm2 UVA 6 h and 72 h after preirradiation with a cumulative dose of 28.8 J/cm2, reduced the proportion of apoptotic cells to 39.6% (c), and 47.9% (d), respectively.