Effect of Lipopolysaccharide Pre-treatment on the Replication of Japanese Encephalitis Virus in Microglia

Abstract

Microglia are resident cells of the central nervous system (CNS) and become
activated to function as brain macrophage in response to infectious pathogens. Our recent
findings further demonstrate that microglia support the replication of Japanese encephalitis
virus (JEV) and remain productively infected for up to 16 weeks. Thus, microglia may serve
as a viral reservoir for JEV infection of neurons in the CNS in addition to provide the first
line of defense against invading pathogens. Interestingly, in the same study, no increase in
nitric oxide levels in the supernatant of microglial cultures was observed following JEV
infection over a 5 day period. This suggests that microglia may not be activated in response
to JEV infection. Therefore, using the same experimental paradigm this study aimed to
determine whether activation of microglia prior to JEV infection would reduce a subsequent
viral production. Briefly, mouse BV-2 microglia were plated at a density of 5×105 cells/well
in 6-well plates. Then, the cultures were treated with lipopolysaccharide (LPS) prior to the
infection with JEV at a MOI of 5 pfu/cell. At 24 h post-infection, the growth media
containing progeny virus were collected for determination of viral titer by standard plaque
assay. Results clearly demonstrated that LPS pre-treatment dramatically reduced viral titer in
the growth media compared with that of infected cultures without LPS pre-treatment. Thus,
cellular activation by LPS prior to the infection appears to reinforce a natural innate immune
mechanism of microglia against JEV infection.