EXPERIMENTAL STUDIES ON IMMUNE RESPONSE IN MICE VACCINATED WITH JAPANESE ENCEPHALITIS VACCINE USED IN THE FIELD. (I)

Abstract

In the past, remarkable difference was encountered in the routine potency tests of the Japanese encephalitis vaccines of two different strains of virus, G-1 and Nakayama, challenged with Nakayama strain. Such result gave us a suggestion of strain difference which might exist in producing immunity in mice.
In order to give answer to such question, the vaccines were prepared with 2 strains, Nakayama and G-1, respectively. Both viruses were identified serologically as Japanese encephalitis viruses. Group of mice were immunized with 2 vaccines, and after the vaccination, cross challenge test was accomplished with both strains on the one hand and on the other, neutralization, complement-fixation and hemagglutination inhibition tests were carried out on sera collected from mice at 2 weeks after the initial vaccination.
As the results, protection index obtained in Nakayama-immunized mice challenged with the heterologous strain at 2 weeks was found to be lower than that obtained by the challenge with homologous one. In case of G-1-immunized mice, the protection index was found very low when challenged either with the homologous strain or with the heterologous one. However, no significant difference was recognized in term of antibody titer between the mice immunized with both strain vaccines.