Screening of high-permissive silkworm strains for efficient recombinant protein production in Autographa californica nuclear polyhedrosis virus (AcNPV)

The baculovirus expression system (BES) using Autographa california nuclear polyhedrosis virus (AcNPV) has been extensively utilized for the high-level expression of sufficient quantities of recombinant proteins in a broad taxonomic range of insect cell lines and insect larvae. In the case of the silkworm, Bombyx mori, however, the BES using AcNPV tends to be much less exploited because AcNPV is believed to be inefficient in the replication of B. mori and cell lines derived from it. In this study, we have searched for high-permissive silkworm strains with higher production levels of a recombinant protein, by screening the susceptibility of 163 silkworm strains to the recombinant AcNPV, which expresses firefly luciferase. Based on their relative luciferase expression levels in larval hemocytes, the silkworm strains tested were divided into 3 groups: 5 high-permissive strains, 74 middle-permissive strains, and 84 low-permissive strains. Among the 5 high-permissive strains (c11, d17, f10, f38, and 1312), d17 was the most productive, showing the luciferase activity of 3.5 × 10⁴ ± 1,764 relative light units (RLU) per microgram of cell proteins. This remarkable susceptibility indicated that the silkworm d17 strain is very useful for large-scale protein production by the BES using AcNPV.