Phagocytosis of
complement-opsonized targets is a primary function of neutrophils at sites of
inflammation, and the clearance of neutrophils that have phagocytosed microbes is important for the resolution of
inflammation. Our previous work suggests that phagocytosis leads to rapid neutrophil apoptosis that is inhibited by antibody to the
beta2 integrin, Mac-1, and requires
NADPH oxidase-derived
reactive oxygen species (ROS) generated during phagocytosis. Here we report that phagocytosis-induced cell death (PICD) does not occur in Mac-1-deficient murine neutrophils, suggesting that PICD proceeds through a bona fide Mac-1-dependent pathway. A sustained, intracellular oxidative burst is associated with PICD. Furthermore, PICD does not require traditional
death receptors, Fas, or
tumor necrosis factor (
TNF) receptor. TNF but not Fas synergizes with phagocytosis to enhance significantly PICD by increasing the oxidative burst, and this is Mac-1-dependent. Phagocytosis-induced ROS promote cleavage/activation of
caspases 8 and 3, key players in most extrinsic ("
death receptor") mediated pathways of apoptosis, and
caspases 8 and 3 but not
caspase 9/mitochondria, are required for PICD. This suggests that ROS target the extrinsic versus the intrinsic ("stress stimulus") apoptotic pathway. Phagocytosis also triggers a competing MAPK/ERK-dependent survival pathway that provides resistance to PICD likely by down-regulating
caspase 8 activation. The anti-apoptotic factor
granulocyte-macrophage colony-stimulating factor (
GM-CSF) significantly enhances ROS generation associated with phagocytosis. Despite this, it completely suppresses PICD by sustaining ERK activation and inhibiting
caspase 8 activation in phagocytosing neutrophils. Together, these studies suggest that Mac-1-mediated phagocytosis promotes apoptosis through a
caspase 8/3-dependent pathway that is modulated by
NADPH oxidase-generated ROS and MAPK/ERK. Moreover, TNF and
GM-CSF, likely encountered by phagocytosing neutrophils at inflammatory sites, exploit pro-(ROS) and anti-apoptotic (ERK) signals triggered by phagocytosis to promote or suppress PICD, respectively, and thus modulate the fate of phagocytosing neutrophils.