Endocytosis is required for exocytosis and priming of respiratory burst activity in human neutrophils.

OBJECTIVE AND DESIGN

Neutrophil generation of reactive oxygen species (ROS) is enhanced by exposure to pro-inflammatory agents in a process termed priming. Priming is depending on exocytosis of neutrophil granules and p47 phosphorylation-dependent translocation of cytosolic NADPH oxidase components. Clathrin-mediated endocytosis was recently reported to be necessary for priming, but the mechanism linking endocytosis to priming was not identified. The present study examined the hypothesis that endocytosis regulates neutrophil priming by controlling granule exocytosis.

MATERIALS AND METHODS

Clathrin-mediated endocytosis by isolated human neutrophils was inhibited by chlorpromazine, monodansylcadaverine, and sucrose. Exocytosis of granule subsets was measured as release of granule components by ELISA or chemiluminescence. ROS generation was measured as extracellular release of superoxide as reduction of ferrocytochrome c. p38 MAPK activation and p47 phosphorylation were measured by immunoblot analysis. Statistical analysis was performed using a one-way ANOVA with the Tukey-Kramer multiple-comparison test.

RESULTS

Inhibition of endocytosis prevented priming of superoxide release by TNFα and inhibited TNFα stimulation and priming of exocytosis of all four granule subsets. Inhibition of endocytosis did not reduce TNFα-stimulated p38 MAPK activation or p47 phosphorylation. Inhibition of NADPH oxidase activity blocked TNFα stimulation of secretory vesicle and gelatinase granule exocytosis.

CONCLUSIONS

Endocytosis is linked to priming of respiratory burst activity through ROS-mediated control of granule exocytosis.