Upregulation of Reactive Oxygen Species Generation and Phagocytosis, and Increased Apoptosis in Human Neutrophils During Severe Sepsis and Septic Shock

We evaluated neutrophil activation by measuring its phagocytic ability and oxidative burst activity in 16 patients with sepsis and 16 healthy volunteers. We also focused on neutrophil apoptosis as a regulatory mechanism of the inflammatory response. Neutrophil phagocytosis was evaluated by the detection of propidium iodide (PI)-labeled Staphylococcus aureus added to whole blood. Reactive oxygen species (ROS) formation was quantified by measuring the oxidation of 2',7' dichlorofluorescein diacetate (DCFH-DA) at baseline and after cell stimulation with phorbol myristate acetate (PMA), and bacterial cells (killed S. aureus) or products (lipopolysaccharide [LPS] and N-formyl-methionyl-leucyl-phenylalanine [FMLP]). Apoptosis was assessed in neutrophils stained with annexin V and PI. Neutrophil phagocytic ability was increased in patients with sepsis compared with healthy controls (median geometric mean fluorescence intensity [GMFI] was 101.9 and 54.7, respectively; P = 0.05). ROS formation was enhanced in patients with sepsis compared with healthy volunteers at baseline (median GMFI 275.6 and 52.1, respectively; P < 0.001), and after stimulation with S. aureus (median GMFI 2395.8 and 454.9, respectively; P < 0.001), PMA (median GMFI 1120.6 and 307.5, respectively; P = 0.003), FMLP (median GMFI 792.4 and 123.2, respectively; P < 0.001), and LPS (median GMFI 624.8 and 144.8, respectively; P < 0.001). Early neutrophil apoptosis was increased in patients with sepsis compared with healthy volunteers (median 11.3% and 9.1%, respectively; P = 0.03). These data demonstrate that neutrophil function is enhanced in patients with sepsis. Additionally, circulating neutrophils from patients with sepsis presented with increased early apoptosis, which may be consequence of a regulatory mechanism of the inflammatory response.