Expression and biological activity assay of bovine interleukin-18 fusion protein

The cDNA of bovine interleukin-18(BoIL-18)was subcloned into pGEX-6P-1 vector and transformed into Escherichia coli BL21(DE3).The recombinant protein was expressed successfully in Escherichia coli by induced with 0.3 mmol/L IPTG for 8 h.SDS-PAGE results indicated that engineering bacteria could express a 44 kD product.And densitometric scanning showed the expressed fusion protein was about 31.8% of total bacterial protein of BL21.The fusion protein was purified by affinity chromatography.Then the biological activity of purified product was assayed.The PBMC(peripheral blood mononuclear cells)proliferation indicated that the BoIL-18 fusion protein could enhance proliferation of PBMC when it was more than 0.10 mg/L.And the ELISA method showed that the BoIL-18 fusion protein could induce IFN-γ production in spleen lymphocyte when it was more than 0.20 mg/L,and the amount of BoIL-18 fusion protein and its inducing effect on IFN-γ had a direct proportion.It can be concluded that the purified BoIL-18 fusion protein has functional activity and can be applied for further studies.