Sephacryl S-300 HR molecular size elution profile of¹²⁵I-GM-CSF bound at variable IgG concentrations.¹²⁵I-GM-CSF, 0.25 ng/mL, was incubated at 37°C for 18 hours with 10 mg/mL (  ), 5 mg/mL (–––), and 0.5 mg/mL (-------) of the same IgG batch. Similar findings were obtained with IgG from all three manufacturers.