The E protein of Japanese encephalitis virus (JEV) is the major antigen to elicit neutralizing antibody response and protective immunity in hosts. In this study, we developed a baculovirus-based expression system of the Japanese encephalitis virus full-length E protein for production of recombinant vaccine. The expression of the full-length JEV E protein was not secreted but produced in the cytoplasm in spite of the use of prM-derived signal peptide. The full-length JEV E protein expressed in insect cells was extensively purified using immobilized metal affinity chromatography and emulsified with Freund's adjuvant for immunological studies. Our studies demonstrated the mice immunized with the full-length JEV E protein successfully induced neutralizing antibody response and protective immunity toward a lethal challenge of the JEV. This finding provides valuable information for developing subunit vaccines for JEV antigenic complex viruses. (C) 2003 Elsevier Inc. All rights reserved.