Recombinant chicken interferon: a potent antiviral agent that lacks intrinsic macrophage activating factor activity.

Crude preparations of chicken interferon (ChIFN) from various sources contain both antiviral and macrophage-activating factor (MAF) activity. Previous serological data indicated that unlike mammals, birds might express only a single type of IFN in response to viruses and mitogens that exhibits both activities. We have now expressed a complementary DNA for virus-induced ChIFN in transfected COS cells and in Escherichia coli. Purified recombinant ChIFN is a powerful antiviral agent and has high Mx promoter-inducing activity. However, as the sole agent, recombinant ChIFN lacks MAF activity: it does not induce the secretion of nitric oxide in primary monocyte-derived chicken macrophages. A neutralizing antiserum prepared against cloned ChIFN blocks most of the antiviral and Mx promoter-inducing activity present in preparations of natural ChIFN, but does not inhibit the MAF activity. These results demonstrate that chicken cells can be induced to secrete a novel cytokine which probably represents the avian homolog of mammalian IFN-gamma.