| IL-18 was lately discovered, involved in induction of production of IFN-γand GM-CSF secreted by T and NK cell and in enforcement of cytotoxic effect of T and NK cell. It has promising prospects application in the fields of anti-tumor, infection of pathogenic microbes as well as hypersensitiveness. In this study, we have obtained the following results:The porcine IL-18 gene was amplified from recombinant plasmid pGEM-IL-18 by PCR, then the fusion expression vector pPIC9K-IL-18 was constructed by inserting IL-18 fragment, and transformed to GS115 by electroporation. Multi-copy recombinant strains were screened by G418. The expression of recombinant fusion protein was induced by methanol, and SDS-PAGE was used to analyze the product. The bioactivity of IL-18 purified by Sephadex G-100, was measured by MTT assay. Experiment results showed the fusion protein of IL-18 secreted by GS115 and reached the expression peak of 160mg/L at 72h. We have expressed and purified successfully the recombinant pIL-18 with obvious biological activity in pichia pastoris.Except the internal characters of heterogenous gene sequence itself, expression conditions also plays important roles in the expression yield. Different culturable time, inducible patterns, pH valves and the amount of inducible reagent were compared on effect of expression in this paper respectively. Experimental results revealed that the fermentation period induced with methanol was 72 h. The optimal concentration of methanol was 20g/L, pH range was 6.0–8.0 and the inoculation amount seed was 1: 1 in shake-flask fermentation. Compared with those induced only with methanol, pattern of inhibition/induction could improve the expression level significantly.This study provides bases on development and application of new type reagent porcine IL-18.
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