Binding of Human Alpha-Interferons to Natural Killer Cells

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Abstract
It has previously been shown that recombinant DNA-derived human leukocyte interferon IFN-αJ, which is active on human cells in antiviral and antiproliferative assays, substantially lacks the ability of other purified leukocyte IFN (e.g., IFN-αA) to enhance natural killer (NK) activity. IFN-αJ can, however, block the boosting of NK activity by IFN-αA, suggesting that IFN-αJ can occupy the IFN-α receptor on NK cells.(1) We demonstrate here directly that IFN-αJ can bind to NK cells and can compete with [125I]IFN-αA for binding sites. The equilibrium dissociation constant (Kd) for IFN-αJ is no more than 20– 30 times greater than for IFN-αA. The relative Kd values for IFN-αA and IFN-αJ are similar when measured with Daudi cells, where both IFN-αs 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-αJ relative to IFN-αA on NK cells following a 2-h incubation.