1959 Volume 9 Issue 2 Pages 124-129
It was assumed that the Japanese encephalitis vaccine of mouse brain type might give rise preventive effect on the disease in nature in approximately 75 per cent. However, such a brain type vaccine was proved to contain possibly some factor to produce demyelinization following inoculation with the vaccine combined with Freund's adjuvant into guinea pigs. Accordingly the minimum requirement of the vaccine was revised to be prepared from the supernatant of 2 per cent emulsion of infected mouse brain following centrifugation at 3, 000 rpm for 30 min. Encephaligenic factor of such vaccine was remarkably minimized so that no more experimental demyelinization in guinea pig was encountered with this.
Herewith an attempt was made to elucidate immune response following injection of formalin killed mouse brain type vaccine of G-1 strain which was prepared following the method of the minimum requirement. G-1 strain of Japanese encephalitis virus was isolated from an encephalitis patient by us in 1949 and had been passed through mouse brain roughly by 200 generations. To criticize immune response by the vaccine, the vaccine was diluted to 1:1, 1:16 and 1:128 or 1:1, 1:10, 1:100 and 1:1, 000 and a group of mice was immunized with each dilution. Those immunized mice were divided into subgroups, and challenged with a series of 10 fold dilution of G-1 strain intracerebrally at 2 and 3 weeks after the initial immunization. On the other hand, neutralization, complement-fixation (CF) and hemagglutination inhibition (HAI) tests were carried out with pooled mouse sera from each group at 2 and 3 weeks after the initial vaccination. By comparing protection index (PI) with neutralization index (NI), CF and HAI antibody titers in mice at 2 and 3 weeks after the immunization with each dilution of the vaccine, those may be said:
1) The less PI and antibody titers were found in mice immunized with the higher dilution of vaccine at 2 weeks.
2) There was no significant difference in immune responses of mice vaccinated with both original and 10 times diluted vaccines. The minimum effective dose of the vaccine in mice was computed to be between 10 and 100 times dilution of the vaccine.
3) Comparing with immune responses each other in mice at 2 and 3 weeks, both PI and CF antibody titers reached their peaks at 2 weeks and fell down by 3 weeks, while both neutralizing and HAI antibody titers were found almost the same.
From the foregoing results it may be suggested that the effect of vaccine should be criticized on the basis of results obtained in mice first immunized with dilutions of vaccine of some range and then challenged with a series of virus dilution.
