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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 live-attenuated 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.
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Figure 1.
The viral titer of Nakayama-NIH, Beijing-1 and JaGAr in VERO cells at 24 hours after infection. The results shown are the averages of three independent assays, with error bars representing the standard deviations.
Figure 2.
The antibodies induced by Nakayama-NIH, Beijing-1 and JaGAr. (A) The neutralizing antibody titer to each JEV. (B) The indirect immunofluorecent analysis to detect JEV antibodies.
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