Neutrophil apoptosis: a marker of disease severity in sepsis and sepsis-induced acute respiratory distress syndrome

Abstract

Introduction: Apoptosis of neutrophils (polymorphonuclear neutrophils [PMNs]) may limit inflammatory injury in sepsis and acute respiratory distress syndrome (ARDS), but the relationship between the severity of sepsis and extent of PMN apoptosis and the effect of superimposed ARDS is unknown. The objective of this study was to correlate neutrophil apoptosis with the severity of sepsis and sepsis-induced ARDS.

Methods: A prospective cohort study was conducted in intensive care units of three tertiary hospitals in Porto Alegre, southern Brazil. Fifty-seven patients with sepsis (uncomplicated sepsis, septic shock, and sepsis-induced ARDS) and 64 controls were enrolled. Venous peripheral blood was collected from patients with sepsis within 24 hours of diagnosis. All surgical groups, including controls, had their blood drawn 24 hours after surgery. Control patients on mechanical ventilation had blood collected within 24 hours of initiation of mechanical ventilation. Healthy controls were blood donors. Neutrophils were isolated, and incubated ex vivo, and apoptosis was determined by light microscopy on cytospun preparations. The differences among groups were assessed by analysis of variance with Tukeys.

Results: In medical patients, the mean percentage of neutrophil apoptosis (+/- standard error of the mean [SEM]) was lower in sepsis-induced ARDS (28% +/- 3.3%; n = 9) when compared with uncomplicated sepsis (57% +/- 3.2%; n = 8; p < 0.001), mechanical ventilation without infection, sepsis, or ARDS (53% +/- 3.0%; n = 11; p < 0.001) and healthy controls (69% +/- 1.1%; n = 33; p < 0.001) but did not differ from septic shock (38% +/- 3.7%; n = 12; p = 0.13). In surgical patients with sepsis, the percentage of neutrophil apoptosis was lower for all groups when compared with surgical controls (52% +/- 3.6%; n = 11; p < 0.001).

Conclusion: In medical patients with sepsis, neutrophil apoptosis is inversely proportional to the severity of sepsis and thus may be a marker of the severity of sepsis in this population.

Figure 1

Apoptosis of neutrophils in a healthy donor and in a patient with sepsis-induced acute respiratory distress syndrome (ARDS). (a) Apoptosis of neutrophils in a healthy donor. Wright's Giemsa staining of cytocentrifuge smear shows predominance of cells in apoptosis. Inset shows morphological detail of an apoptotic cell, with loss of chromatin fine granularity (condensation) and karyorrhexis. (b) Apoptosis of neutrophils in a patient with sepsis-induced ARDS. Wright's Giemsa staining of cytocentrifuge smear shows predominance of normal-looking cells. Inset shows morphological detail of a normal cell, with fine granularity of chromatin and normal lobulated nucleus. Magnifications ×200 (insets ×500).

Figure 2

Mean percentage of neutrophil apoptosis in medical patients. There was a statistically significant difference among the groups (p < 0.001; analysis of variance). The differences between individual groups as determined by a post hoc Tukey test are illustrated. ARDS, acute respiratory distress syndrome.

Figure 3

Mean percentage of neutrophil apoptosis in surgical patients. There were statistically significant differences among the groups (p < 0.001; analysis of variance). Post hoc Tukey test results are illustrated. ARDS, acute respiratory distress syndrome.