Screening of protective antigens of Japanese encephalitis virus by DNA immunization: a comparative study with conventional viral vaccines

In this study, we evaluated the relative role of the structural and nonstru ctural proteins of the Japanese encephalitis virus (JEV) in inducing protec tive immunities and compared the results with those induced by the inactiva ted JEV vaccine. Several inbred and outbred mouse strains immunized with a plasmid (pE) encoding the JEV envelope protein elicited a high level of pro tection against a lethal JEV challenge similar to that achieved by the inac tivated vaccine, whereas all the other genes tested, including those encodi ng the capsid protein and the nonstructural proteins NS1-2A, NS3, and NS5, were ineffective. Moreover, plasmid pE delivered by intramuscular or gene g un injections produced much stronger and longer-lasting JEV envelope-specif ic antibody responses than immunization of mice with the inactivated JEV va ccine did. Interestingly, intramuscular immunization of plasmid pE generate d high-avidity antienvelope antibodies predominated by the immunoglobulin G 2a (IgG2a) isotype similar to a sublethal live virus immunization, while ge ne gun DNA immunization and inactivated JEV vaccination produced antienvelo pe antibodies of significantly lower avidity accompanied by a higher IgG1-t o-IgG2a ratio. Taken together, these results demonstrate that the JEV envel ope protein represents the most critical antigen in providing protective im munity.