Binding of B7-1 IgG to the tumor membrane by means of high-affinity FcγRI.

U937 cells were preincubated with B7-1 IgG in the absence or presence of the CD64-blocking mAb 197. After extensive washing of the cells, membrane-bound B7-1 IgG was detected by FACS analysis with mAb 104/CD80. CD8 IgG was used as a negative control. The figure shows a representative FACS histogram of this experiment with a B7-1 IgG–to–197 mAb ratio of 1:10.