Biological and immunological studies on two substrains, c-1 and c-3, derived from the Nakayama-NIH strain of Japanese encephalitis virus.

A comparative analysis was performed on two substrains, c-1 and c-3, derived from the Nakayama-NIH strain of Japanese encephalitis virus. The infectivity of the two substrains was inactivated at similar rates by treatment with Tween 80 and Tween 20 but not by treatment with Tween 60. However, hemagglutinating activity as measured at pH 6.8 of the c-3 substrain treated with Tween 80 was more labile than that of the c-1 substrain treated with Tween 80. Also, the immunogenicity (neutralizing and hemagglutination-inhibiting antibodies) was different between the two substrains in sensitivity to low pH (6.8) and to Tween 80. With the c-1 substrain a combination of these treatments reduced the immunogenicity, but each treatment applied singly did not materially reduce it. The immunogenicity of the c-3 substrain was reduced by single as well as combined applications of the two treatments. Evidence was obtained which suggested that the part of the antigen sensitive to these treatments was strain-specific, whereas the resistant antigen was common among the Japanese encephalitis-St. Louis encephalitis complex members.