Abstract
All strains of Japanese B encephalitis virus had been thought to have the same antigenic properties. During routine work in the National Assay of vaccine in potency, it was noticed that there was a difference in resisting ability between products of vaccine originated from the same Nakayama strain. In order to determine whether or not any antigenic difference might be present between the two Nakayama strains (one stored at the National Institute of Health, Ministry of Health and Welfare, and the other at the National Veterinary Assay Laboratory, Ministry of Agriculture and Forestry), immunological tests were performed. Interesting results were obtained as follows. 1. In cross protection test with the method prescribed in the Minimum Requirements for Vaccine and the modified method of Habel's test, immunized mice showed a higher resistance to homologous virus than heterologous-virus challenge. Such difference was more remarkable in highly immunized animals than in lowly immunized ones. No difference was observed between both vaccines in resisting ability against the virus which was isolated in the recent epidemics in Japan. 2. Such antigenic difference between both vaccines was also observed in cross neutralization test with the serum of immunized guinea-pig. 3. No antigenic discrepancy was observed in hemagglutination, hemagglutination-inhibition, and complement-fixation tests. No differences were shown between both viruses in precipitation test with protamine sulfate and sensitivity test with desoxycholate. There was no sign of contamination with any other virus. From these results, it was presumed that part of the antigenicity, especially resisting ability and neutralization properties, could cause some change so that a different type might be produced in the course of long serial passage.
