Research Paper Volume 3, Issue 4 pp 407—416

Figure 1. Senescent human fibroblasts contain markers of DNA damage response in vitro. (A) Low passage neonatal normal human fibroblasts (PD-5), stress-induced senescent fibroblasts (PD-5, H₂O₂), and replicatively senescent fibroblasts (PD-40) were stained for the presence of senescence-associated β-galactosidase activity (blue), with α-53BP1 antibodies (multiple punctate nuclear staining), or α--p21 antibodies (bar = 20 µm). (B) The percentage of senescent cells were determined for senescence-associated β-galactosidase and 53BP1 staining. 53BP1-positive cells contained at least four individual fluorescent pin-point spots per nucleus (asterisks indicate significant difference from PD-5 cells, p <0.001, two-tailed t-test).