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

Interferon-&#x03B3; (IFN-&#x03B3;), 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-&#x03B3;-inducing factor, is a cytokine that induces T and natural killer cells to produce IFN-&#x03B3;. In this study, the chicken IL-18 (ChIL-18) and chicken IFN-&#x03B3; (ChIFN-&#x03B3;) genes were inserted into the pET28a prokaryotic expression vector, resulting in pET28a-IL-18 and pET28a-IFN-&#x03B3;, respectively. These plasmids were transformed into <i>Escherichia coli </i>strain BL21, and the ChIL-18 and ChIFN-&#x03B3; proteins were expressed and purified. To determine their antiviral activities, 200 ng/mL of ChIL-18 and/or ChIFN-&#x03B3; 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-&#x03B3; in combination was better than that of ChIL-18 or ChIFN-&#x03B3; alone. Next, 14-day-old chicken were injected with 200 µg of ChIL-18 and/or ChIFN-&#x03B3; 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-&#x03B3;, as evidenced by cytokine detection, quantitative PCR, and pathology analyses. These results indicate that ChIL-18 and ChIFN-&#x03B3; could inhibit IBDV infection and the combination of ChIL-18 and ChIFN-&#x03B3; has a better inhibitory effect than either cytokine alone.