Antigenic comparison of strains of Japanese encephalitis virus (JEV) was carried out using the modi -fied hemagglutination-inhibition technique of Casals (Grid HI test). Eight of these JEV strains were isolated from different areas of Japan (Tokyo, Kyoto, Fukuoka, and Gunma Prefecture), and one from Thai land. The strains were isolated from different hosts over a period of 30 years. Antigens for the test were obtained from suckling mice brain by the sucrose-acetone method, and specific hyperimmune sera were prepared in adult mice.
The results obtained are as follows:
1. Nakayama-Yoken strain showed an optimum pH of 6.15-6.40 in hemagglutinin activity, and the others a pH of 6.45-6.75.
2. It was found that the final pH of the system in hemagglutination-inhibition test, after the suspen sion of erythrocytes had been added, influenced the results of the test; the inhibitory action of the serum increased with the pH in the limits of an optimum pH of its antigen.
3. There was significant antigenic difference between Nakayama-Yoken strain and Nakayama-RFVL, JaGAr 01, and the recently isolated strains. Hemagglutinins of the latter strains were inhibited by Nakayama-Yoken antiserum but the HI titer of the serum was not so high as when tested against the-homologous antigen. On the other hand, antigen of the Nakayama-Yoken strain was inhibited by anti -sera of the other strains with a titer nearly that of the homologous system. It has been believed that Nakayama-Yoken and Nakayama-RFVL strain, the representative strains of JEV, had the same origin, and it was suggested that the antigenic characteristics of the former had been changed in the course of long passage.
4. There was slight antigenic difference between Nakayama-RFVL strain and JaGAr 01 or the recently isolated strains, but antigenically they were closely related each other.
5. Considerable antigenic discrepancy was present between JaGAr 01 strain and the recently isolated strains, and it was demonstrated that the latter had broader antigenic composition than the former.
6. No antigenic difference was observed among the six recently isolated strains.
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