Expressions of I antigen and CD15 and CD71 markers in K-562 cells expressing wild-type and mutant C/EBPα. Wild-type C/EBPα and C/EBPα mutants with respective substitutions of S21A, S21D, S234A, and S234D were expressed in K-562 cells cultured in noninducing conditions. Expressions of cell-surface I antigen and CD15 and CD71 markers on the K-562 cells were analyzed by the use of flow cytometry and detected with monoclonal anti-I (1:15 dilution), anti-CD15 (1:200 dilution), and anti-CD71 (1:200 dilution) antibodies, respectively, with the bound antibodies on the cell surfaces revealed by 1:200 dilution of FITC-conjugated goat anti–human IgM, anti–mouse IgM, and anti–mouse IgG antibodies, respectively. The open and shaded areas represent results obtained from cells incubated with first antibody and FITC-conjugated secondary antibody, and with FITC-conjugated secondary antibody only, respectively. The geometric MFI detected is shown on the top of each peak.