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Open Access Research

Protective immunity to Japanese encephalitis virus associated with anti-NS1 antibodies in a mouse model

Yize Li1, Dorian Counor1, Peng Lu1, Veasna Duong2, Yongxin Yu3 and Vincent Deubel14*

Author Affiliations

1 Key Laboratory of Molecular Virology and Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, 20025, China

2 Unit of Virology, Institut Pasteur in Cambodia, Phnom Penh, Cambodia

3 National Institute for the Control of Pharmaceutical and Biological Products, Tiantan Xili Chongwen Qu, Beijing, 100050, China

4 Present address: Institut Pasteur in Cambodia, Phnom Penh, Cambodia

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Virology Journal 2012, 9:135  doi:10.1186/1743-422X-9-135

Published: 24 July 2012

Abstract

Background

Japanese encephalitis virus (JEV) is a major mosquito-borne pathogen that causes viral encephalitis throughout Asia. Vaccination with an inactive JEV particle or attenuated virus is an efficient preventative measure for controlling infection. Flavivirus NS1 protein is a glycoprotein secreted during viral replication that plays multiple roles in the viral life cycle and pathogenesis. Utilizing JEV NS1 as an antigen in viral vectors induces a limited protective immune response against infection. Previous studies using E. coli-expressed JEV NS1 to immunize mice induced protection against lethal challenge; however, the protection mechanism through cellular and humoral immune responses was not described.

Results

JEV NS1 was expressed in and purified from Drosophila S2 cells in a native glycosylated multimeric form, which induced T-cell and antibody responses in immunized C3H/HeN mice. Mice vaccinated with 1 μg NS1 with or without water-in-oil adjuvant were partially protected against viral challenge and higher protection was observed in mice with higher antibody titers. IgG1 was preferentially elicited by an adjuvanted NS1 protein, whereas a larger load of IFN-γ was produced in splenocytes from mice immunized with aqueous NS1. Mice that passively received anti-NS1 mouse polyclonal immune sera were protected, and this phenomenon was dose-dependent, whereas protection was low or delayed after the passive transfer of anti-NS1 MAbs.

Conclusion

The purified NS1 subunit induced protective immunity in relation with anti-NS1 IgG1 antibodies. NS1 protein efficiently stimulated Th1-cell proliferation and IFN-γ production. Protection against lethal challenge was elicited by passive transfer of anti-NS1 antisera, suggesting that anti-NS1 antibodies play a substantial role in anti-viral immunity

Keywords:
Japanese encephalitis virus; T-cell response, Antibodies; Monoclonal antibodies; NS1 protein; Mouse model