Fragment of Japanese encephalitis virus envelope protein produced in Escherichia coli protects mice from virus challenge

A fragment from the N-terminal part (EA) and a fragment from the C-terminal part (EB) of the envelope (E) protein of Japanese encephalitis virus (JEV) was synthesized in Escherichia coli. These two fragments were overlapping with each other by nine amino acids, however, they were not cross-reacting with each other at the antisera level. Both EAand EBare antigenic by themselves when injected into mice, but when tested against sera from mice, rabbit, swine and human that had been immunized or naturally infected with JEV, EBacted as a better antigen than EAby ELISA assays. EBalso proved to be a better immunogen in protection against lethal JEV infection than EA. The protection appears to be correlated with the neutralizing titres of the anti-JEV sera. The response elicited by EBis a Th1 response and the antibody produced contained higher neutralizing titre than EAfragment. The major difference between EAand EBfragments is the solubility during expression inE. coli , while EBfragment is soluble, EAwas isolated from the insoluble inclusion bodies. Therefore the antigenicity and immunogenicity expressed by the EBfragment may probably be due to its proper folding to assume a correctly assembled form during expression in E. coli, a quality that is important for a protein to qualify as a good vaccine candidate.