Effect of IgG on the binding of GM-CSF to GM-CSF-R. Data are expressed as specific ¹²⁵I-GM-CSF bound to cells versus free cytokine—in the absence of IgG (X), or presence of Gammagard (○), Sandoglobulin (▵), or Nordimmun (□). Five different batches of IgG from each manufacturer were tested in parallel. HL-60 cells were incubated with 3,900 cpm/200 μL and 1.25 mg/mL of IgG, or with decreasing concentrations of the tracer alone. PMN were treated as the HL-60 cells, except that they were coincubated with 4 mg/mL of IgG at 2,900 cpm/200 μL. The background binding was assessed with excess Ab to GM-CSF-R. Data are means of duplicates and representatives of two to five experiments.