ABSTRACT
The Japanese encephalitis virus (JEV), a member of the Flaviviridae family and Flavivirus genus, is transmitted by mosquitoes. JEV, of which some 35,000 cases are recorded every year, is a positive RNA virus. Two types of JEV vaccines have been developed to prevent the onset of encephalitis in humans, namely formalin-inactivated and liveattenuated vaccines. JEV inactivated vaccines are usually made using the Nakayama-NIH or Beijing-1 strains of the JEV virus. In this study, the immunological response to the Nakayama-NIH and Beijing-1 strains was analyzed as part of the effort to compile basic data which could lead to the selection of a suitable vaccine strain. To this end, the virus titer of Beijing-1 was found to be two-fold higher than that of Nakayama-NIH by plaque assay. Moreover, Beijing-1-induced neutralizing antibodies showed a higher level of titers when confronted by Korean JEV isolates than Nakayama-NIH-induced neutralizing antibodies (1:320 vs. 1:160, respectively). However, as a minimum ratio of 1:10 neutralizing antibody titers are required to protect against JEV infection, both strains in effect exhibited a sufficient level of neutralizing antibody titers. What's more, Beijing-1 was found to induce a somewhat higher cytotoxic T lymphocyte (CTL) response than Nakayama-NIH. Taken together, this can be taken to mean that Beijing-1 may in fact be a more effective vaccine candidate strain when it comes to inducing a high level of protective immunity against JEV infection.