Interleukin-8-induced suppression of polymorphonuclear leukocyte apoptosis is mediated by suppressing CD95 (Fas/Apo-1) Fas-1 interactions.
BACKGROUND
Neutrophil apoptosis is crucial in the resolution of inflammation. The role of interleukin (IL)-8 in neutrophil apoptosis has not been previously studied; we hypothesized that in addition to its role as a chemoattractant, IL-8 would regulate polymorphonuclear leukocyte (PMN) apoptosis.


METHODS
PMNs were adhered to plastic during hypoxia or normoxia and treated with IL-8 dosages of 0 to 1000 ng/mL. Apoptosis was assessed by cellular histology and the TUNEL assay. For receptor inhibition, blocking antibodies to IL-8 receptors in the presence of IL-8 were added. Apoptosis of PMNs treated with anti-Fas antibody +/- IL-8 was also analyzed.


RESULTS
After treatment with 100 ng/mL IL-8 apoptosis was decreased from an average of 39.1% 9.3%. Inhibition of IL-8RA was able to restore apoptosis to 59.4%. Western analysis showed that with IL-8, there was a marginal decrease of total Fas protein, whereas Fas ligand was increased. After incubation with an apoptosis inducing-Fas antibody plus IL-8 reduced apoptosis to 9.5%.


CONCLUSIONS
IL-8 not only promotes the inflammatory response by recruiting PMNs but also acts to suppress apoptosis mainly through the IL-8RA in an oxygen tension independent manner. The reduction in apoptosis is associated with changes in Fas and FasL where the presence of IL-8 suppresses the proapoptotic function of Fas-FasL interactions.
Brown University School of Medicine, Rhode Island Hospital, Department of Surgery, Providence 02903, USA.
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Leuenroth
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Keeping
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Simms
D048868:Adaptor Proteins, Signal Transducing; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002352:Carrier Proteins / Q000032:analysis / Q000378:metabolism; D053143:Caspase 2; D053148:Caspase 3; D020169:Caspases; D015687:Cell Hypoxia / Q000502:physiology; D003546:Cysteine Endopeptidases / Q000032:analysis / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D053222:Fas Ligand Protein; D053200:Fas-Associated Death Domain Protein; D006801:Humans; D016209:Interleukin-8 / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000032:analysis / Q000378:metabolism; D009504:Neutrophils / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology; D011506:Proteins / Q000032:analysis / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D016159:Tumor Suppressor Protein p53 / Q000032:analysis / Q000378:metabolism; D019014:fas Receptor / Q000032:analysis / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C505533:FADD protein, human; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D053200:Fas-Associated Death Domain Protein; D016209:Interleukin-8; D008562:Membrane Glycoproteins; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D019014:fas Receptor; C505407:CASP3 protein, human; D053143:Caspase 2; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases; D010100:Oxygen