Binding of human alpha-interferons to natural killer cells.

It has previously been shown that recombinant DNA-derived human leukocyte interferon IFN-alpha J, which is active on human cells in antiviral and antiproliferative assays, substantially lacks the ability of other purified leukocyte IFN (e.g., IFN-alpha A) to enhance natural killer (NK) activity. IFN-alpha J can, however, block the boosting of NK activity by IFN-alpha A, suggesting that IFN-alpha J can occupy the IFN-alpha receptor on NK cells. We demonstrate here directly that IFN-alpha J can bind to NK cells and can compete with [125I]IFN-alpha A for binding sites. The equilibrium dissociation constant (Kd) for IFN-alpha J is no more than 20-30 times greater than for IFN-alpha A. The relative Kd values for IFN-alpha A and IFN-alpha J are similar when measured with Daudi cells, where both IFN-alphas have potent antiproliferative effects. This suggests that the difference in receptor binding on NK cells in terms of equilibrium binding constants does not explain the inactivity of IFN-alpha J relative to IFN-alpha A on NK cells following a 2-h incubation.