Prokaryotic Expression and Anti-IBDV Activity of Chicken Interleukin-18 and Interferon-γ

Interferon-γ (IFN-γ), a cytokine produced by activated natural killer cells and T lymphocytes, is an important regulator of innate and adaptive immunity. Interleukin (IL)-18, also known as IFN-γ-inducing factor, is a cytokine that induces T and natural killer cells to produce IFN-γ. In this study, the chicken IL-18 (ChIL-18) and chicken IFN-γ (ChIFN-γ) genes were inserted into the pET28a prokaryotic expression vector, resulting in pET28a-IL-18 and pET28a-IFN-γ, respectively. These plasmids were transformed into Escherichia coli strain BL21, and the ChIL-18 and ChIFN-γ proteins were expressed and purified. To determine their antiviral activities, 200 ng/mL of ChIL-18 and/or ChIFN-γ were inoculated into chicken embryonic fibroblast cells. After 24 h, one 50% tissue culture infective dose (TCID50) of infectious bursal disease virus (IBDV) was inoculated into the chicken embryonic fibroblast cells. The results showed that the antiviral effect of ChIL-18 and ChIFN-γ in combination was better than that of ChIL-18 or ChIFN-γ alone. Next, 14-day-old chicken were injected with 200 µg of ChIL-18 and/or ChIFN-γ and then were challenged with 103 TCID50 of IBDV via intraperitoneal injection. The results showed that the proliferation of IBDV was inhibited by the injection of the recombinant proteins, especially the combination of ChIL-18 and ChIFN-γ, as evidenced by cytokine detection, quantitative PCR, and pathology analyses. These results indicate that ChIL-18 and ChIFN-γ could inhibit IBDV infection and the combination of ChIL-18 and ChIFN-γ has a better inhibitory effect than either cytokine alone.