Contrasting phagosome pH regulation and maturation in human M1 and M2 macrophages.
Bottom Line: The paucity of V-ATPases in M1 phagosomes was associated with, and likely caused by, delayed fusion with late endosomes and lysosomes.The delayed kinetics of maturation was, in turn, promoted by the failure of M1 phagosomes to acidify.By contrast, M2 phagosomes proceed to acidify immediately in order to clear apoptotic bodies rapidly and effectively.
Affiliation: Program in Cell Biology, Hospital for Sick Children, Toronto, ON M5G 0A4, Canada.Show MeSH
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Mentions: The net generation of ROS is much greater in M1 than in M2 macrophages not only because of their higher NOX2 content, but also because the oxidase remains active longer. This became apparent when monitoring the rate of superoxide generation over time in single phagosomes, incubating the cells in the presence of subsaturating concentrations of NBT (1 μg/ml for M1 and 10 μg/ml for M2 macrophages). Using bright-field microscopy, we could estimate the rate of formazan deposition by acquiring images at regular intervals and quantifying the progressive decrease in pixel intensity. As illustrated in Figure 3A and summarized in Figure 3, B and C, whereas M1 phagosomes generate ROS continuously for at least 30 min, the oxidase activity of M2 phagosomes becomes undetectable after 5–10 min.
Affiliation: Program in Cell Biology, Hospital for Sick Children, Toronto, ON M5G 0A4, Canada.