Priming of the Neutrophil Respiratory Burst Involves p38 Mitogen-activated Protein Kinase-dependent Exocytosis of Flavocytochrome b ₅₅₈-containing Granules*

The respiratory burst of human neutrophils is primed by a number of pro-inflammatory stimuli, including tumor necrosis factor-α (TNFα) and lipopolysaccharide (LPS); however, the mechanism of priming remains unknown. LPS has been shown previously to increase membrane expression of flavocytochromeb ₅₅₈, a component of the NADPH oxidase. This study shows that TNFα also increases membrane expression of flavocytochrome b ₅₅₈. Mitogen-activated protein kinase (MAPK) modules have been implicated in the action of priming agents. Pharmacologic inhibitors of MAPKs, SB203580 and PD098059, revealed that priming of the respiratory burst and up-regulation of flavocytochrome b ₅₅₈ are dependent on p38 MAPK but not on extracellular-signal regulated kinase (ERK). TNFα and LPS primed respiratory burst activity and increased membrane expression of CD35 and CD66b, specific markers of secretory vesicles and specific granules that contain flavocytochrome b ₅₅₈, with similar time courses and concentration dependences. These processes also required p38 MAPK but were independent of ERK. TNFα failed to prime respiratory burst activity or to increase membrane CD35 expression in enucleated neutrophil cytoplasts. These data suggest that one mechanism by which TNFα and LPS prime neutrophil respiratory burst activity is by increasing membrane expression of flavocytochromeb ₅₅₈ through exocytosis of intracellular granules in a process regulated by p38 MAPK.