Flow cytometric analysis of the effect of silkworm hemolymph on the baculovirus-induced insect cell apoptosis

The effect of silkworm hemolymph on the inhibition of baculovirus-induced insect cell apoptosis was quantitatively investigated using a flow cytometric analysis. Spodoptera frugiperda (Sf9) cell and Autographa californica nuclear polyhedrous virus (AcNPV) were used as a model for insect cell and baculovirus in this study, respectively. Compared with a mammalian cell cycle, the fraction of G1 cells was relatively small in the Sf9 cell cycle. Silkworm hemolymph did not affect the Sf9 cell-cycle distribution before the baculovirus infection. However, the fraction of cells which are not in the sub-G1 phase remained at a high level for 3 days after the infection in the medium without silkworm hemolymph, while it remained at a high level for 7 days after the infection in the medium supplemented with silkworm hemolymph. The fractions of apoptotic cells in the sub-G1 phase were 4.7%, and 4 days after infection, 22.7%, in the media with and without silkworm hemolymph, respectively.