Spontaneous in contrast to CD95-induced neutrophil apoptosis is independent of caspase activity.

Background: The influence of caspase inhibitors on spontaneous and on CD95-triggered apoptosis was investigated in neutrophils from healthy volunteers and compared with neutrophils from patients with severe sepsis.
Methods: To further elucidate the mechanisms of neutrophil apoptosis, isolated neutrophils from healthy volunteers (n = 9) were either stimulated with the agonistic anti-CD95 antibody (100 ng/mL) or left unstimulated in the presence or absence of the caspase inhibitors zIETD-fmk (10 micromol/L), zDEVD-fmk (10 micromol/L), or zVAD-fmk (20 micromol/L). Apoptosis was determined by measuring DNA fragmentation and Annexin-V binding in FACS, and caspase-3-like activity by DEVD-afc cleavage assay. Results were compared with those from patients with severe sepsis (n = 15).
Results: Reduced spontaneous neutrophil apoptosis in patients with sepsis (-48.7%) was completely restored by incubation with agonistic anti-CD95 antibody (p < 0.05). Inhibition of caspases did not influence spontaneous neutrophil apoptosis in both groups. However, zVAD-fmk reduced anti-CD95 antibody-induced apoptosis in neutrophils from controls by -22.6% (p < 0.05) and in patients with sepsis by -43.1% (p < 0.05).
Conclusion: These results indicate that spontaneous in contrast to CD95-induced neutrophil apoptosis is independent of caspase activity.