Characterization of receptors for human recombinant interferon-.GAMMA. in human cells.

Highly purified human recombinant interferon-γ (ReIFN-γ) was radioiodinated with <SUP>125</SUP>I-Bolton-Hunter reagent and used to characterize the receptor for ReIFN-γ. <SUP>125</SUP>I ReIFN-γ specifically and saturably bound four human cells tested, FL, WISH, Daudi, and HL-60, which were reported to have ReIFN-γ binding sites. Scatchard analysis of the binding data of FL cells revealed the presence of 5200 binding sites per cell and a K<SUB>d</SUB> value of 2.1×10<SUP>-10</SUP>M. Although the binding of <SUP>125</SUP>I ReIFN-γ was inhibited by unlabelled natural IFN-γ and ReIFN-γ, it was not inhibited by unlabelled human ReIFN-α and ReIFN-β, suggesting that receptors for (Re) IFN-γ were different from those for IFN-α or IFN-β. However, ReIFN-γ displaced the binding of <SUP>125</SUP>I ReIFNγ 3 to 5 times more effectively than IFN-γ. Internalization of <SUP>125</SUP>I ReIFN-γ bound to the cell surface receptor was observed at 37°C. Pretreatment of FL cells with unlabeled ReIFN-γ caused a concentration-dependent down-regulation in the ReIFN-γ receptor, which was specific for IFN-γ and reversible. From these studies, we concluded that although the ReIFN-γ is not identical to putative IFN-γ, the recombinant form binds to the same binding sites for IFN-γ and does not bind to the binding sites for IFN-α or β.