IFN receptor binding affinity between sensitive and resistant Huh-7 cell lines. Equal numbers of cured cells were incubated with different concentrations (3.9 to 125 ng) of 125I-IFN-α2b at 37°C for one hour. Non-specific binding was measured in presence of 100-fold excess of unlabeled IFN-α2b for each dilution. Cells were washed twice in PBS. Radioactivity (cpm) of each cell pellet was measured. The amount of interferon specifically bound was determined by subtracting non-specific binding from total binding. Specific binding of 125I-IFN-α2b to three groups of resistant cell lines and one sensitive cell line are shown (A-D).