Establishment and characterization of Japanese B encephalitis virus persistent infection in the Sf9 insect cell line

The Sf9 cell line, commonly used for gene expression by recombinant baculoviruses, can be productively infected by Japanese B encephalitis virus (JEV). Two wild-type JEV strains (P3 and SA14) caused a cytopathic effect (CPE) in the Sf9 cells, while no apparent CPE was caused by an attenuated strain (SA14-14-2). The JEV viral antigens were expressed in the infected Sf9 cells and intracellular virus particles were found by electron microscopy as a result of infection with all three strains. Titres of cell-associated and cell-free supernatant virus remained stable for relatively long periods of cultivation, suggesting that both wild-type and attenuated JEV strains established productive and persistent infections of Sf9 cells. The JEV produced by the Sf9 cells could be neutralized by anti-JEV reference serum, but relatively smaller plaques were formed in BHK21 cells infected with JEV that had been cultivated long term in Sf9 cells. This system for virus propagation has a number of potentially important uses for enhancing progress in JEV study and control.