Hydrogen peroxide reverses IL-5 afforded eosinophil survival and promotes constitutive human eosinophil apoptosis

Background: Eosinophils play a central role in the induction and perpetuation of allergic inflammatory responses. The present study was performed to investigate the effects of reactive oxygen intermediates on constitutive apoptosis as well as on interleukin (IL)-5 afforded human eosinophil survival. Methods: Peripheral blood eosinophils were isolated by CD16-negative selection to >99% purity and were cultured for 48 h. The number of apoptotic eosinophils in the culture was assessed by flow cytometric analysis of relative DNA content in propidium-iodide-stained cells, annexin-V binding or by morphological analysis. Apoptosis was confirmed by the appearance of a typical ladder pattern in the DNA fragmentation assay by agarose gel electrophoresis. Results: Exogenous H₂O₂ reversed IL-5-afforded eosinophil survival by inducing apoptosis. Constitutive eosinophil apoptosis was inhibited by a reduction of intracellular levels of H₂O₂ by catalase. Exogenous H₂O₂ increased the rate of constitutive apoptosis. Conclusions: Our results suggest that H₂O₂ may play a role in the downregulation of eosinophilic inflammation by inducing eosinophil apoptosis.