Particulate vaccine candidate for Japanese encephalitis induces long-lasting virus-specific memory T lymphocytes in mice.

We previously reported that extracellular particles (EPs) composed of premembrane (prM) and envelope (E) proteins were released from cells infected with recombinant vaccinia viruses encoding Japanese encephalitis (JE) virus prM and E genes. In the present study, EPs were evaluated for induction of JE virus-specific antibody and specific T lymphocytes in mice. Six- to 8-week-old male Balb/c mice were inoculated intraperitoneally once or twice (at a 3-week interval) with purified EPs containing 1 microgram of E without adjuvant. Neutralizing antibody was detected and spleen cells proliferated against JE viral antigen 3 weeks after the second immunization with EPs. Neutralizing antibody and JE virus-specific T lymphocytes were also detected 10 months after immunization with EPs containing 2 micrograms of E. Spleen cells obtained from EP-immunized mice and stimulated in vitro with live JE virus, expressed JE virus-specific cytotoxic activity. The cytotoxic activity was reduced by treatment with anti-CD3 antibody and complement. These results indicate that immunization with EPs induces long-lasting specific antibody and memory T cells in mice.