Efficient production of biologically active porcine interleukin-18 by coexpression with porcine caspase-1 using a baculovirus expression system.

We previously reported that the precursor form of porcine interleukin-18 (IL-18) expressed by the baculovirus system was able to be secreted efficiently into the supernatant of insect cells, whereas only small amounts of mature IL-18 were secreted from insect cells. As insect cells do not normally have the IL-1beta converting enzyme (caspase-1), which is required for processing of the precursor IL-18 into the mature IL-18, we recently cloned porcine caspase-1 cDNA. In this study, we constructed a recombinant baculovirus containing the cDNA encoding porcine caspase-1 and showed that the coexpression of caspase-1 and the precursor IL-18 enabled insect cells to secrete mature IL-18 into the culture supernatant efficiently. Moreover, inhibition of caspase-1 activity by its specific inhibitor prevented the processing of precursor IL-18 into the mature form. These results indicated that the processing and secretion of precursor IL-18 into the mature form in insect cells were enhanced by the artificial introduction of caspase-1 activity for cleavage.