Lanthanide ion enhancement of interferon binding to cells

Pretreatment of purified [ 125I]-labeled human and mouse β interferons (IFN) with lanthanum chloride (LaCl 3) enhanced 20–30 fold the binding of the [ 125I]-IFNs to human A549 and mouse L cells at 0°C and also enhanced antiviral activity in homologous cells. Although lanthanides enhanced cross-species binding of both human and mouse [ 125I]-IFNs, there was no increase in cross-species antiviral activity. Unlabeled IFN not treated with LaCl 3 did not compete with [ 125I]-IFN treated with LaCl 3 for cellular receptors. However, unlabeled IFN treated with LaCl 3 did compete with LaCl 3-treated [ 125I]-IFN. These results suggest that lanthanide treated IFNs do not bind to the same receptors as native IFNs.