Expression of Nix and Bcl-xL protein in the erythroid precursor cells. Immunostaining was performed on cytospin preparations of primary human erythroid precursor cells (“Materials and methods”). (A) May-Grünwald-Giemsa staining of air-dried (unfixed) cytospin preparations to demonstrate erythroid maturity. (B) Cells were fixed and stained in the absence of a primary antibody (negative control). (C) Cells were immunostained with anti–Bcl-xL antibody. (D) Cells were immunostained with anti-Nix antibody. Peroxidase (rust)–tagged secondary antibodies were used for detection in panels B to D. Bar indicates 10 μm.