Comparison of biological activities of natural and recombinant chicken interferon-gamma

In recent years, chicken interferon-gamma (ChIFN-γ) has been identified and cloned from a chicken T cell line. In this study, recombinant ChIFN-γ produced in the baculovirus and prokaryotic (Escherichia coli) expression systems were characterized and their activity was compared to that of naturally ChIFN-γ produced by mitogen-activated splenic T cells. The baculovirus-derived ChIFN-γ protein (Bac-ChIFN-γ) proved to have physiochemical properties and biological activities similar to those of natural ChIFN-γ. Indeed, Bac-ChIFN-γ was able to inhibit the replication of cytolytic viruses in chicken embryo fibroblasts and to activate macrophages, as was determined by nitric oxide production. Levels ranging between 100 and 300 μg/ml of BacChIFN-γ could be obtained in the supernatants of infected insect cells. On the other hand, yields of the E. coli produced ChIFN-γ rarely exceeded 100 μg/ml after purification steps and although it was also able to activate the HD11 macrophage cell line in a specific manner, no anti-viral activity could be demonstrated. Therefore, the baculovirus expression system is an appropriate system for the high-level expression of biologically active ChIFN-γ and will allow further studies of the immunomodulatory and therapeutic effects of this cytokine in vivo.