Protection of Mice against Japanese Encephalitis Virus Group II Strain Infections by Combinations of Monoclonal Antibodies to Different Antigenic Domains on Glycoprotein E

A combination of at least three hemagglutination-inhibition-positive (HAI) and virus-specific (Hs) monoclonal antibodies (MAbs) to glycoprotein E (gpE) of Japanese encephalitis virus (JEV) fully protected (100%) mice against JEV strain 733913 infections (group 1). However, these representative epitopes are reported to have been lost on JEV group II strains. In the present study, therefore, the protective effect of various combinations of anti-gpE MAbs representing antigenic epitopes other than Hs was studied on mice infections with JEV group II strains: JEV strains 641686 and 691004. MAbs used in the protective experiments were characterized as HAI-negative virus-specific (NHs) and HAI-positive flavivirus cross-reactive (Hx). Additionally, one of the Hs MAbs (MAb Hs-3) was included in the experiments. Mice were first administered single MAbs or their combinations intraperitoneally and 24 h later, infected with the virus intracerebrally. Protection rates of 70–75% were obtained with a combination of four MAbs: MAbs NHs-1, Hx-1, Hx-3 and Hs-3. However, protection rates of only 20–40% were obtained with three MAbs but none was observed with single or two MAbs. There was, however, a substantial increase in mice survival. The protective effect of several combinations of anti-gpE MAbs representing different antigenic epitopes might be due to the enhancement of binding within the same group and also between different MAb groups. The present results indicate that NHs and Hx epitopes should be incorporated with three Hs epitopes in a JEV vaccine that would have an added advantage, particularly in the flaviviral endemic areas with JEV strain variations.