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

A fragment from the N-terminal part (E_A) and a fragment from the C-terminal part (E_B) 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 E_A and E_B are 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, E_B acted as a better antigen than E_A by ELISA assays. E_B also proved to be a better immunogen in protection against lethal JEV infection than E_A. The protection appears to be correlated with the neutralizing titres of the anti-JEV sera. The response elicited by E_B is a Th1 response and the antibody produced contained higher neutralizing titre than E_A fragment. The major difference between E_A and E_B fragments is the solubility during expression in E. coli, while E_B fragment is soluble, E_A was isolated from the insoluble inclusion bodies. Therefore the antigenicity and immunogenicity expressed by the E_B fragment 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.