To determine whether the IFN produced and secreted after a longer period of infection was active, culture supernatants from U373MG-EV cells (SEV) and U373MG-PMLIV cells (SPMLIV) infected with VSV for 20 h were tested, in comparison with IFN-β, for their capacities to induce ISG products and to inhibit viral protein synthesis. This evidence concerns the gene IFNA1 and infection.