Role of reactive oxygen species in neutrophil apoptosis following ingestion of heat-killed Staphylococcus aureus.

Neutrophils, short-lived leucocytes that die by apoptosis, play an important role in the first stage of defense against bacterial infections. It has been reported that phagocytosis of intact bacteria or Candida albicans can accelerate neutrophil apoptosis. However, the mechanism of phagocytosis-mediated neutrophil apoptosis is not well characterized. In this study, we evaluated whether ingestion of heat-killed Staphylococcus aureus (S. aureus) enhances neutrophil apoptosis and whether this type of apoptosis is mediated by oxidative stress by using antioxidants and polymorphonuclear leucocytes (PMNs) from patients with chronic granulomatous disease (CGD). Co-culture of PMNs with varying doses of S. aureus resulted in accelerated PMN death in a dose- and time-dependent manner. Increased PMN apoptosis was observed by both Annexin V and PI staining. Similar results were observed in PMNs of CGD patients. Dimethyl sulphoxide (DMSO, an OH* scavenger) did not significantly inhibit either S. aureus-ingested PMN apoptosis or spontaneous PMN apoptosis. On the other hand glutathione (GSH, an H2O2 scavenger) significantly inhibited both types of apoptosis. Our findings suggest that oxygen-independent pathways may mainly operate in the process of phagocytosis-induced apoptosis.