IL-5 prevents both cytochrome c release and Bax translocation to the mitochondria during spontaneous eosinophil apoptosis.
Eosinophils were coincubated in the presence or absence of either STS (10−5 M) or IL-5 (10−10 M) and z-VAD.fmk (100 μM) for the indicated times and the cells assessed for evidence of cytochrome c release (A,B) or Bax translocation to the mitochondria (C,D). Cytochrome c and Bax were detected by immunohistochemistry as described in “Materials and methods.” The percentage of eosinophils exhibiting diffuse cytochrome cand aggregated Bax distribution were quantified by fluorescence microscopy. IL-5 inhibited cytochrome c release and Bax translocation observed during spontaneous eosinophil apoptosis after 24 and 48 hours. Quantification of subcellular localization in eosinophils exposed to STS for longer than 6 hours was not possible. STS rapidly induced cytochrome c release and Bax translocation after 2 hours, which was not inhibited by z-VAD.fmk. Results are expressed as the mean ± SE of 3 separate experiments. Asterisk indicates IL-5– or STS-treated eosinophils compared with the relevant untreated or z-VAD.fmk–treated control (P < .05).
