VARIABILITY OF STRAINS OF JAPANESE ENCEPHALITIS VIRUS IN REGARD TO THE PH-DEPENDENCY IN HEMAGGLUTINATION

Abstract
One hundred and twelve strains of Japanese encephalitis virus (JEV) isolated in Japan during the past 25 years were tested for hemagglutination (HA) with the suckling mouse brain antigen. In the pattern HA tests of a checkerboard system employing graded pH, most of the strains showed about equal titers in the pH range of 6.0 to 7.0, the maximum titers being obtained usually at pH 6.8. In contrast, 7 strains which had received more frequent passages than the rest indicated a different pattern in which the HA titers at the neutral pH were much lower than those at the acid pH, resulting in demonstration of the peak titers at pH 6.2 to 6.4. Analyses of the phenomenon have suggested, however, that the pH-dependency of JEV HA is a genetically stable property, being characteristic to each strain. It is highly probable that the pH-dependency of JEV HA may be an expression of the physicochemical properties of the virus particle which control its adsorbing action onto red cells.