Confocal images to show the phagocytosis of ROS by polarized hES-RPE (passage 3) derived from hES-3 stem cell line compared to nonpolarized hES-RPE. The polarized and nonpolarized hES-RPE cells were challenged with FITC-labeled ROS (green) at different time points. Lysosomes were labeled with fluorescent dye (red), and nuclei were labeled with DAPI (blue). The phagocytosis assay revealed that there were no FITC-ROS containing phagosomes in either polarized or nonpolarized hES-RPE cells after a 1-hour challenge (A, D). FITC-ROS containing phagosomes appeared in polarized hES-RPE cells as early as 6 hours after ROS challenge (B), whereas they did not appear in nonpolarized hES-RPE at the same time period after ROS challenge (E). After 20 hours of FITC-ROS treatment, the labeled phagosomes reached the highest numbers inside polarized hES-RPE cells and many of them fused with red lysosomes (yellow; C), whereas few FITC-ROS containing phagosomes were found inside nonpolarized hES-RPE cells (F). Images are representative of experiments performed in triplicate.