FL protein is expressed by human leukemia/lymphoma cell lines and primary AML blasts. Cells (1 × 10⁶) were fixed, permeabilized, and stained with either anti-FL or isotype control antibody followed by staining with PE-conjugated secondary antibody. The stained cells were then analyzed by flow cytometry. The open histogram represents staining with isotype control. The shaded histogram represents staining with anti-FL antibody. (A) Left panel shows the expression of FL in the ML-1 cell line. Right panel shows the results of staining the same cells with anti-FL antibody that had been preincubated with FL for 16 hours. (B) FL expression by several leukemia cell lines. (C) FL expression by several primary AML samples.