Short communication Effect of ba®lomycin A1 on the growth of Japanese encephalitis virus in Vero cells

We studied the effect of ba®lomycin A1 (Baf-A1), a novel and highly speci®c inhibitor for vacuolar-type proton (V-H) pump, on the growth of Japanese Encephalitis virus (JEV) in Vero cells. Viral ̄uorescence microscopic study showed that Baf-A1 induced the complete disappearance of acidi®ed compartments such as endosomes and lysosomes in Vero cells by the treatment with 0.1 mM Baf-A1 for 1 h at 378C. In proportion to the disappearance of acidi®ed compartments, virus growth was inhibited when Baf-A1 was present from 1 h before infection to the end of incubation in a dose-dependent manner, or added within as early as 5 min after infection. Conversely, the virus growth was recovered in correlation with the reappearance of acidi®ed compartments after removal of Baf-A1. These results suggest that a low pH condition, which is regulated by Baf-A1-sensitive V-H pumps, is essential for the early stage of JEV growth.