Characterization of receptors for human recombinant interferon-gamma in human cells

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