Inoculation of plasmids encoding Japanese encephalitis virus PrM-E proteins with colloidal gold elicits a protective immune response in BALB/c mice.

We established a simple and effective method for DNA immunization against Japanese encephalitis virus (JEV) infection with plasmids encoding the viral PrM and E proteins and colloidal gold. Inoculation of plasmids mixed with colloidal gold induced the production of specific anti-JEV antibodies and a protective response against JEV challenge in BALB/c mice. When we compared the efficacy of different inoculation routes, the intravenous and intradermal inoculation routes were found to elicit stronger and more sustained neutralizing immune responses than intramuscular or intraperitoneal injection. After being inoculated twice, mice were found to resist challenge with 100,000 times the 50% lethal dose (LD(50)) of JEV (Beijing-1 strain) even when immunized with a relatively small dose of 0.5 micro g of plasmid DNA. Protective passive immunity was also observed in SCID mice following transfer of splenocytes or serum from plasmid DNA- and colloidal gold-immunized BALB/c mice. The SCID mice resisted challenge with 100 times the LD(50) of JEV. Analysis of histological sections detected expression of proteins encoded by plasmid DNA in the tissues of intravenously, intradermally, and intramuscularly inoculated mice 3 days after inoculation. DNA immunization with colloidal gold elicited encoded protein expression in splenocytes and might enhance immune responses in intravenously inoculated mice. This approach could be exploited to develop a novel DNA vaccine.