PGE2 and dibutyryl cyclic adenosine monophosphate prolong eosinophil survival in vitro.
Peacock, Craig D. PhD; Misso, Neil L. A. PhD; Watkins, D. Neil PhD, FRACP; Thompson, Philip J. FRACP
[Article] Journal of Allergy & Clinical Immunology. 104(1):153-162, July 1999.

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Background: Apoptosis represents a mechanism by which the accumulation and inflammatory potential of eosinophils in asthma might be limited. Mediators derived from the airway epithelium may influence the rate of eosinophil apoptosis.

Objective: We have investigated the effects on eosinophil apoptosis of 3 mediators that are likely to be produced by the airway epithelium, namely PGE2, TNF-[alpha], and nitric oxide.

Methods: Peripheral blood eosinophils from healthy adult volunteers were purified by density gradient centrifugation and negative immunomagnetic selection. Eosinophils were cultured for 16 or 40 hours with PGE2 (10 nmol/L), dibutyryl cyclic adenosine monophosphate (AMP; 100 [mu]mol/L), TNF-[alpha] (500 U/mL), the nitric oxide donors, S-nitroso-N-acetylpenicil-lamine (100 [mu]mol/L), and 2,2'-(hydroxynitrosohydrazono)bisethanamine (1 mmol/L), or dibutyryl cyclic guanosine monophosphate (100 [mu]mol/L). Control cultures consisted of untreated, IL5-treated (100 U/mL), and anti-Fas-treated (400 ng/mL) cells. Eosinophil apoptosis was assessed by flow cytometric analysis of annexin V-FITC binding to externalized phosphatidylserine, by electrophoresis of phosphorus 32 end-labeled DNA fragments, and by flow cytometric assessment of hypodiploid DNA with propidium iodide.

Results: PGE2 and cyclic AMP inhibited spontaneous eosinophil apoptosis at both 16 and 40 hours as did the PGEP2 receptor agonist, 11-deoxy PGE1, at 40 hours, but these effects were not inhibited by a protein kinase A antagonist. TNF-[alpha] delayed apoptosis in eosinophil cultures at 16 hours, whereas S-nitroso- N-acetylpenicillamine, 2,2'-(hydroxynitrosohydrazono)bis-ethanamine, and cyclic guanosine monophosphate had little effect. Anti-Fas had little effect on spontaneous eosinophil apoptosis but significantly reduced the inhibitory effects of PGE2, cyclic AMP, and TNF-[alpha]. Assessments of apoptosis by DNA fragmentation gave similar but quantitatively less sensitive results.

Conclusion: Inhibition of spontaneous eosinophil apoptosis by PGE2 appears to be mediated by EP2 receptors but is not protein kinase A dependent. By enhancing eosinophil survival, PGE2 may increase the proinflammatory potential of these cells in chronic asthma.

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