IFNγ downregulates ¹²⁵I-rhSCF–specific binding to ECFCs. The effect of rhIFNγ on ¹²⁵I-SCF–specific binding was examined to determine the affinity and number of SCF receptors. Day-5 ECFCs were incubated with 2,500 U/mL of rhIFNγ for 24 hours and then specific binding of ¹²⁵I-rhSCF was measured. The level of ¹²⁵I-rhSCF–specific binding in the rhIFNγ group (•) was significantly lower than in the control group (○). Scatchard analysis shows a single class of SCF receptors in both groups, with reduction of the receptor number after rhIFNγ treatment, but no effect on the kd. A summary of triplicate experiments is shown in Table 1. ECFC purity in this experiment was 53% ± 7% in the control group and 48% ± 1% in the rhIFNγ group.