Figure 2. The time-dependent effects of subtoxic levels of hydrogen peroxide on release of interleukin-6 by retinal pigment epithelium cells. Retinal pigment epithelium (RPE) cells (ARPE-19) were plated into 24-well plates. After 24 h incubation, 100 µM hydrogen peroxide (H₂O₂) was added to the culture and incubated for 2, 6, 12, and 24 h. Conditioned culture medium was collected and the amount of interleukin-6 (IL-6) protein in the conditioned medium was determined by using the human IL-6 Quantikine enzyme-linked immunosorbent assay (ELISA) kit. IL-6 levels in conditioned culture medium were expressed as pg/ml (mean±standard deviation in triplicate tests). *0.01< p<0.05, **p<0.01, compared with the controls (cells cultured without H₂O₂).