Bax translocates to the mitochondria during spontaneous and STS-induced eosinophil apoptosis.

Immunocytochemistry was performed, as described in “Materials and methods,” on fixed cytospins of freshly isolated eosinophils (A,B) or eosinophils cultured in the absence (C) or presence of IL-5 (10⁻¹⁰ M) for 6 hours (D) or STS (10⁻⁵M) for 2 hours (E). Images were captured by confocal microscopy at × 100 magnification under oil immersion. Eosinophils were stained with monoclonal anti–Bax 6A7 (A,C-E) or isotype-matched control (B), and the mitochondria and nuclei stained with Mitotracker CMXRos and Hoechst 33258, respectively (A-E). Colocalization (yellow) of Bax (green) and mitochondria (red) was observed in single sections. Culturing in the absence of IL-5 for 6 hours and treatment with STS for 2 hours induced Bax translocation to the mitochondria. Bar represents 10 μm. Results are representative of experiments performed on 4 separate donors.