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J. Virol., Jan 1998, 191-200, Vol 72, No. 1
YL Lin, LK Chen, CL Liao, CT Yeh, SH Ma, JL Chen, YL Huang, SS Chen and HY Chiang
Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, is a
zoonotic pathogen that is prevalent in some Southeast Asian countries and
causes acute encephalitis in humans. To evaluate the potential application
of gene immunization to JEV infection, we characterized the immune
responses from mice intramuscularly injected with plasmid DNA encoding JEV
glycoproteins, including the precursor membrane (prM) plus envelope (E)
proteins and the nonstructural protein NS1. When injected with the plasmid
expressing prM plus E, 70% of the immunized mice survived after a lethal
JEV challenge, whereas when immunized with the plasmid expressing NS1, 90%
of the mice survived after a lethal challenge. As a control, the mice
immunized with the DNA vector pcDNA3 showed a low level (40%) of
protection, suggesting a nonspecific adjuvant effect of the plasmid DNA.
Despite having no detectable neutralizing activity, the NS1 immunization
elicited a strong antibody response exhibiting cytolytic activity against
JEV-infected cells in a complement-dependent manner. By contrast,
immunization with a construct expressing a longer NS1 protein (NS1'),
containing an extra 60-amino- acid portion from the N terminus of NS2A,
failed to protect mice against a lethal challenge. Biochemical analyses
revealed that when individually expressed, NS1 but not NS1' could be
readily secreted as a homodimer in large quantity and could also be
efficiently expressed on the cell surface. Interestingly, when NS1 and NS1'
coexisted in cells, the level of NS1 cell surface expression was much lower
than that in cells expressing NS1 alone. These data imply that the presence
of partial NS2A might have a negative influence on an NS1-based DNA
vaccine. The results herein clearly illustrate that immunization with DNA
expressing NS1 alone is sufficient to protect mice against a lethal JEV
challenge.
Copyright © 1998, American Society for Microbiology
DNA immunization with Japanese encephalitis virus nonstructural protein NS1 elicits protective immunity in mice
Institute of Preventive Medicine, National Defense Medical Center, Taipei, Taiwan, Republic of China. yll@ms11.hinet.net
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