Anti-hTfR IgG3-Av down-regulates TfR expression on the surface of ARH-77 cells. Cells treated with buffer (•), 11 nM anti-hTfR IgG3 (▪), or 11 nM anti-hTfR IgG3-Av (▴) were harvested at 4, 12, 24, 48, and 72 hours. Cells were then incubated with Tf-FITC, washed, and analyzed by flow cytometry. This experiment was repeated twice with similar results.