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Figure 4: Confocal analysis of LysoTracker-treated THP-1 cells infected with P. acnes. To visualize acidified cellular compartments the acidotropic dye LysoTracker Red DND-99 was used (red). Intracellular P. acnes were stained in green. Colocalization of P. acnes and LysoTracker, indicative of an acidified P. acnes-containing phagosome, was apparent at 6 h p.i. (yellow/orange) but not at 2 h and 24 h p.i. Shown are representative images from two independent infection experiments.