Expression of Bcl-x in CD34⁺ cells undergoing granulocyte or monocyte/macrophage differentiation. Cells were cultured as described in Fig 1, and at the indicated time points, Bcl-x protein was analyzed by an immunocytochemical procedure using a rabbit antibody against human Bcl-x. After incubation with biotinilated goat antirabbit IgG and ExtrAvidin alkaline phosphatase, staining was developed using BCIP/NBT substrate (original magnification × 1,000). No signal was detectable in the negative controls. All stainings are from a representative experiment (n = 3).