*From the Thomas Jefferson University Hospital, Philadelphia, PA.
Correspondence to: James Zangrilli, MD, FCCP, Thomas Jefferson University, Rm 805, College Bldg, 1025 Walnut St, Philadelphia, PA 19107; e-mail: email@example.com
Eosinophils undergo spontaneous apoptosis in the absence of specific cytokines, which is further accelerated by Fas engagement and glucocorticoids. We have previously shown that interleukin (IL)-5 profoundly affects the processing of caspase 3 in eosinophils, a downstream executioner of apoptosis, but the level of inhibition is unclear.1 We hypothesized that IL-5 would affect the kinetics of receptor-mediated apoptosis vs non-receptor-mediated apoptosis differently and that this would be reflected by differential activation of elements presumed to be unique to these pathways.
Human peripheral blood eosinophils were cultured in media alone (control), IL-5 (1 ng/mL), dexamethasone (Dex; 1 μmol/L), or agonist anti-Fas antibody (500 ng/mL). Viability by trypan, and the processing of caspases 8, 9, and the apoptosis regulatory protein Bid by immunoblot assay were determined at 8, 24, and 48 h. Bid also was examined in fixed eosinophils by immunochemistry.
Anti-Fas and Dex accelerated cell death compared to media alone. IL-5 blocked Dex-induced cell death and slowed cell death induced by anti-Fas. Caspase 8, 9, and Bid processing occurred during both anti-Fas and Dex treatment. Bid was processed to a similar extent during both anti-Fas and Dex stimulation. Furthermore, Dex treatment caused an early shift in cellular Bid staining from its baseline diffuse cytoplasmic pattern to an increasingly punctate one.
Caspases 8, 9, and Bid were processed efficiently in the absence of obvious activation of the Fas receptor, suggesting alternative mechanisms for caspase 8 activation. IL-5 had the ability to modulate the caspase activation at several levels.
Abbreviations: Dex = dexamethasone; IL = interleukin
This research was supported by National Institutes of Health grants HL03663 and AI24509, and by the Merck Young Investigator Award.
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