Cloning and expression of the chicken interferon-gamma gene

We have cloned the gene for chicken interferon-gamma (ChIFN-gamma) from a cDNA expression library generated from a T cell line (CC8.1h) that produces high levels of IFN-gamma activity. CC8.1h constitutively produces IFN activity that shares physiochemical properties with mammalian IFN-gamma. ChIFN-gamma, when secreted by CC8.1h or expressed in transfected COS cells, is heat labile, inactivated by exposure to pH 2, and capable of inducing nitrite production by chicken macrophages. These properties clearly distinguish it from chicken and mammalian type I IFN. The ChIFN-gamma gene codes for a predicted mature protein of 145 amino acids with a molecular mass of 16.8 kD. There are two potential N-glycosylation sites located near the N terminus. ChIFN-gamma protein shares significant amino acid homology with mammalian IFN-gamma proteins; in particular it also contains the highly conserved motifs that are present in all mammalian IFN-gamma proteins. ChIFN-gamma is 35 and 32% identical to the equine and human counterparts, respectively, but shares only 15% homology with chicken type I IFN. These findings show that the emergence of the two principal types of IFN predates the divergence of avians and mammals that occurred some 350 million years ago.