Figure 2. Effect of phagocytosed particles on the sensitivity of ARPE-19 cell populations to H₂O₂-induced toxicity. Dynamic changes in propidium iodide (PI) fluorescence (in arbitrary units [AU]) are shown in ARPE-19 cells containing no particles (X's) or pre-loaded by phagocytosis with latex beads (triangles) during treatment with 500 μM H₂O₂. For no particle versus bead containing cells, respectively, time of onset of cell death (3.8±0.5 versus 4.2±0.2 h) did not differ, but mean slopes (1630 versus 1013) and peak fluorescence intensities (2430± 394 versus 3422±420) differed significantly (unpaired t tests with equal variances, p<0.02).