Neither Fas ligand nor endotoxin is responsible for inducible peritoneal phagocyte apoptosis during sepsis/peritonitis

Regulation of the phagocyte apoptotic response appears to play a significan t role in the pathophysiology of sepsis. In this regard, prior studies have shown that the onset of phagocyte apoptosis, as well as those agents that regulate it at the nidus of infection, differ significantly from those seen in circulation. The aim of this study therefore was to determine if the in crease in inducible phagocyte apoptosis and caspase activities seen in the peritoneum during sepsis is due to endotoxin or Fas ligand. To study this, male C3H/HeN (endotoxin-sensitive), C3H/HeJ (endotoxin-tolerant), and C3H/H eJ-FasL(gld) (endotoxin-tolerant/FasL-deficient)mice were subjected to ceca l ligation and puncture or sham operation. Twenty-four hours later, phagocy tes were collected and cultured with lipopolysaccharide (LPS), then harvest ed for apoptosis (propidium iodide cell cycle or cell death ELISA analysis) , cytokine release (ELISA), and caspase activity (fluorogenic assay) determ ination. The data indicate that there was a marked increase in apoptosis in LPS-stimulated phagocytes which was associated with a significant increase in caspase 3, 8, and 9 activities but a decrease in caspase 1 activity fro m C3H/HeN and C3H/HeJ-FasL(gld) septic mice and an increase in caspase 3 an d 8 activities in phagocytes from C3H/HeJ septic mice. Furthermore, cells f rom septic mice, including all three strains, lost their ability to produce IL-1 beta and IL-6 in response to LPS stimulation. The inability to comple tely suppress these changes suggests that neither endotoxin (via signaling through TLR-4 pathway) nor Fas ligand regulates the peritoneal phagocyte ap optotic responses seen during the late phase of polymicrobial sepsis/perito nitis. (C) 2000 Academic Press.