Circulating granulocyte macrophage colony-stimulating factor in plasma of patients with the systemic inflammatory response syndrome delays neutrophilapoptosis through inhibition of spontaneous reactive oxygen species generation

In the normal resolution of an acute inflammatory response apoptosis of neu trophils is essential to maintain immune homeostasis and limit inappropriat e host tissue damage by decreasing neutrophil tissue load, function, and re lease of phlogistic reactive oxygen species and proteases. The systemic inf lammatory response syndrome (SIRS), a massive pro-inflammatory immune state , is associated with delayed neutrophil apoptosis, however, the systemic ci rculating factors and intracellular signal transduction pathways important in regulating neutrophil apoptosis in SIRS are poorly described. Neutrophil s isolated from patients with SIRS on admission to the intensive care unit showed significantly (p < .01) delayed spontaneous neutrophil apoptosis com pared with healthy neutrophils as quantified using annexin V-FITC and termi nal deoxyuridine triphosphate (dUTD) nick end labeling (TUNEL) flow cytomet ry methods. Plasma from SIRS patients markedly (41.5 +/- 7.2%, p < .01) inh ibited apoptosis of healthy neutrophils compared with controls (69.7 +/- 4. 8%) indicating the presence of soluble circulating factors that can modify the expression of neutrophil apoptosis. Various pro-inflammatory (IL-6, gra nulocyte macrophage colony-simulating factor, interleukin (IL)-1 beta, tumo r necrosis factor-a) mediators, known to modulate neutrophil apoptosis in v itro, were elevated in the plasma of our cohort of SIRS patients compared w ith controls. However, the anti-apoptotic effect of SIRS plasma was specifi cally attenuated (75.5%, p < .01) by neutralizing SIRS plasma of granulocyt e macrophage-colony-stimulating factor, but not IL-6, IL-1 beta, tumor necr osis factor-ct. Although the anti-inflammatory cytokine IL-10 was elevated in SIRS plasma (median level 7.2 pg/mL), further boosting SIRS plasma with recombinant human IL-10 (10 ng/mL, levels found in septic shock patients) s ignificantly countered (63.8%, p < .01) the inhibitory effect of SIRS plasm a on neutrophil apoptosis. Suppression of neutrophil apoptosis was concomit ant with delayed spontaneous elevation of reactive oxygen species, quantifi ed as peroxide production, and reversed by addition of neutralizing antibod ies to GM-CSF, and recombinant human IL-10 to SIRS plasma. These results id entify circulating GM-CSF as a significant inhibitor of neutrophil apoptosi s in patients with SIRS, and that this effect can be countered by boosting SIRS plasma with IL-10. GM-CSF and IL-10 appear to modulate neutrophil apop tosis by altering reactive oxygen species generation in neutrophils.