Interleukin 8 (IL-8) and growth-related oncogene alpha (Gro-a) delay neutrophil apoptosis, which is thought to be important for the resolution of inflammation. We hypothesized that (IL-8) and Gro-a interfere with extracellular death receptor signaling or intracellular caspase activation to suppress neutrophil apoptosis. In addition, we sought to determine if prolonged neutrophil half-life was associated with preservation of function. Polymorphonuclear leukocytes (PMN) were cultured with IL-8 or Gro-a (0–100 ng/mL) in normoxia or hypoxia, and the extent of apoptosis was assessed by histology and TdT-mediated dUTP nick end labeling (TUNEL). Subsequently, to determine the role of apoptotic-associated receptors, PMN were cultured with IL-8 and neutralizing monoclonal antibody to Fas (CD95), TNFR55, and TNFR75. To establish the effect of IL-8 or Gro-α on pro-apoptotic caspase activity, the cleavage of specific colorimetric substrates was assessed. Functional changes in PMN included the capacity to produce superoxide anion and phagocytosis of Escherichia coli. At the 100 ng/mL dose, the addition of IL-8 and Gro-α maximally suppressed PMN apoptosis from 54% (untreated) to 5% and 6%, respectively. The addition of neutralizing antibodies to Fas, TNFR55, or R75 caused no change in IL-8 suppression of apoptosis. Caspase 3 activity was markedly suppressed at 24 h by the inclusion of either IL-8 and Gro-a. IL-8 and Gro-a-stimulated PMN released more superoxide anion and had an increased phagocytic index vs. control PMN. IL-8 and Gro-α suppress neutrophil apoptosis to a similar level that is not influenced by oxygen tension at high doses. The effect of IL-8 and Gro-a does not depend on activation of the Fas, TNFR55, or R75 receptor pathways but involves suppression of caspase 3 activity. IL-8 or Gro-α extends the functional half-life of neutrophils and may explain their role in disease states such as acute respiratory distress syndrome.
Received 6 May 1999; first review completed 18 Jun 1999; accepted in final form 20 Aug 1999
Address reprint requests to Annmarie L. Dunican, MD, Department of Surgery, 593 Eddy Street, Providence, RI 02904.
Supported by National Institutes of Health grant GM53114 (H.H.S.).
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