GST-FasLs fusion protein binding to untreated (A and C) and anti-CD3–treated (B and D) 3DO cells. GST fusion protein was prepared and biotinylated as described in Materials and Methods. Serial dilutions of GST (A and B) or GST-FasLs (C and D) and streptavidin-FICT 1:50 were used to stain 3DO cells. Inhibition of GST-FasLs biotin (25 μg/μL) binding with anti-Fas MoAb (5 μg/μL) (E). The numbers above the marker represent the percentage of FITC⁺ cells of a representative experiment as calculated by Lysis II. The doses of GST and GST-FasLs fusion proteins are shown on the top of the figure.