PARENCHYMAL-CELL APOPTOSIS AS A SIGNAL FOR SINUSOIDAL SEQUESTRATION AND TRANSENDOTHELIAL MIGRATION OF NEUTROPHILS IN MURINE MODELS OF ENDOTOXIN AND FAS-ANTIBODY-INDUCED LIVER-INJURY

Endotoxin (ET) induces neutrophil sequestration in hepatic sinusoids, the activation of proinflammatory transcription factors (nuclear facto r KB [NF-kappa B]) with up-regulation of adhesion molecules on sinusoi dal endothelial cells and hepatocytes, However, if galactosamine (Gal) is co-administered with ET neutrophils transmigrate and attack parenc hymal cells. This suggests that a signal from parenchymal cells trigge rs neutrophil transmigration. In this study, we tested the hypothesis that parenchymal cell apoptosis may induce neutrophil transendothelial migration in the Gal/ET model. Treatment of C3Heb/FeJ mice with 700 m g/kg Gal and 100 mu g/kg ET induced tumor necrosis factor alpha (TNF-a lpha) formation (13.25 +/- 0.75 ng/mL) and hepatic NF-KB activation at 90 minutes; the generation of the C-X-C chemokine KC (2.86 +/- 0.30 n g/mL at 5 hours); sinusoidal neutrophil sequestration (380 +/- 21 poly morphonuclear leukocytes/50 high-power fields) and apoptosis (925% +/- 29% increase of DNA fragmentation; and a 45-fold increase of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)- positive cells) at 6 hours, followed by transmigration of neutrophils and development of substantial necrosis (38% +/- 3% of hepatocytes; al anine transaminase [ALT]: 1,500 +/- 300 U/L) at 7 hours. Administratio n of uridine (1,000 mg/kg) did not reduce plasma levels of TNF-alpha a nd KC, NF-kappa B activation, or polymorphonuclear leukocyte sequestra tion, but attenuated apoptosis by 90% to 94%, In these livers, neutrop hils did not transmigrate and liver injury was prevented (necrosis: < 5%; ALT: 40 +/- 3 U/L). However, massive apoptosis and liver injury in itiated by the anti-Fas antibody, Jo2, did not recruit neutrophils int o the liver. We conclude that excessive parenchymal cell apoptosis rep resents an important signal for transmigration of primed neutrophils s equestered in sinusoids during endotoxemia in vivo. However, apoptosis per se does not cause neutrophil sequestration in the liver vasculatu re.