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Published online before print September 22, 2006

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(Journal of Leukocyte Biology. 2006;80:1575-1583.)
© 2006 by Society for Leukocyte Biology

In vivo regulation of neutrophil apoptosis by C5a during sepsis

University of Michigan Medical School, Department of Pathology, Ann Arbor, Michigan, USA

¹ Correspondence: Department of Pathology, The University of Michigan Medical School, 1301 Catherine Road, Ann Arbor, MI 48109-0602, USA. E-mail: grf{at}med.umich.edu or pward{at}umich.edu

Delayed neutrophil apoptosis is characteristic of sepsis and may accentuate organ injury. It has been shown that PI-3K and MAPK pathways provide survival signaling in neutrophils. In this study, we demonstrate that neutrophils isolated from septic rats are resistant to apoptosis in comparison with the cells from normal animals. In contrast to normal serum, septic sera induced strong phosphorylation of AKT and p44/42 in neutrophils obtained from normal rats, resulting in marked resistance of these cells to apoptosis. Protection from apoptosis by septic sera was abrogated completely by inhibition of PI-3K and partially diminished by MEK inhibition. Increased neutrophil survival in septic rats was associated with increased levels of Bcl-xL in neutrophils and decreased levels of Bim expression. In vivo blockade of C5a in cecal ligation and puncture rats by anti-C5a antibody markedly restored the susceptibility of neutrophils to undergo apoptosis. C5a activated AKT and p44/42 and also enhanced X-linked inhibitor of apoptosis expression in neutrophils. LPS and C5a were able to induce Bcl-xL expression. Thus, neutrophil survival signals derived from effects of septic sera could be linked to activation of ERK1/2 and PI-3K, increased antiapoptotic protein expression, and ultimately, delayed neutrophil apoptosis.

Key Words: cell signaling • survival • phagocyte • inflammation

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