Purification and Characterization of Chick Embryo Interferon

Summary Chick embryo interferon was purified from allantoic fluid of embryonated eggs infected with influenza A virus. Purification consisted essentially of acid precipitation to remove virus and extraneous protein, concentration and purification by precipitation with Zn++, column chromatography on CM-cellulose, and zone ionophoresis on pevikon. The interferon was purified 4500 times with respect to initial protein and one unit of interferon activity was 0.0042 μg protein in the chick embryo cell-EEE virus assay system used. Interferon was found to be a slightly basic protein of low molecular weight and free of nucleic acid as well as constituents giving absorption in the visible spectrum. A trace amount of carbohydrate was found. Detailed findings in the analyses are presented. The striking difference in properties of interferon from those described heretofore by other workers appears to lie in previous failure of purification. Both crude and purified chick interferon were active in suppressing Rous sarcoma development and NDV virus infection in susceptible chicks but were without therapeutic effect.