Iron supplement blocks the antiproliferative and proapoptotic effects of anti-hTfR IgG3-Av. (A) ARH-77 and IM-9 cells were treated for 72 hours with 11 nM anti-hTfR IgG3-Av alone or in the presence of 30 μM zinc sulfate (ZnSO₄) or 25 μM ferric ammonium citrate (FAC). The cells were then cultured in the presence of [³H]-thymidine for an additional 24 hours and harvested, and the incorporation of [³H]-thymidine was determined. Each value is the mean of quadruplicate samples expressed as the percentage of the control mean (controls are cells treated with buffer alone, with or without metal salt supplement; data not shown). (B) ARH-77 cells were treated for 96 hours with buffer or 11 nM anti-hTfR IgG3-Av with or without 50 μM FAC. The cells were then washed, stained with annexin V-Alexa Fluor 488 and PI, and analyzed by flow cytometry. The percentage of cells located in each quadrant is shown at the corner.