Fig. 2. Aging is associated with increased ROS, inflammation factors and decreased proliferation. (A) Proliferation curve of WI-38 fibroblasts. (B) Early-passage cells (<25 PD) were defined as young because only 10% were positive for SA-β-Gal staining. Late-passage cells (>40 PD) were defined as senescent cells because more than 90% of the cells were positive for SA-β-Gal staining. (C) The ROS levels at early and late passages. (D) The TNF-α levels at early and late passages. (E) The IL-6 levels at early and late passages. (F) Cell proliferation shows the characteristic EdU staining. Data are presented as means ± SD (n = 3). *P < 0.05 compared with young.