Immunologic Studies of Japanese Encephalitis Virus in Japan

Abstract

Summary Following inapparent infection by Japanese encephalitis virus in August and September 1956, 14 children without preexisting JE virus neutralizing antibody, developed a primary hemagglutination-inhibition antibody response by November; 13 of the 14 children formed neutralizing antibody and 11 of 14 children developed complement fixing antibody. Neutralizing antibody usually appeared concurrently with HI antibody, though in some children it appeared before or after HI antibody. Inapparent “reinfections” by JE virus occurred during August and September 1956 in seven children with preexisting neutralizing antibody in plasma. The HI and neutralizing antibody responses were similar in time of occurrence and frequency to those seen in the 14 children without preexisting neutralizing antibody; however, complement fixing antibody more promptly and uniformly rose to detectable levels in the “reinfected” children than in the group with primary infection. Although the exact mechanism of antibody stimulation following “reinfection” of humans by JE virus is uncertain, this phenomenon may play a role in Japan in maintenance of JE virus antibody levels and immunity in humans and possibly in animals. Maximal HI antibody titers that develop within two months of inapparent infection were lower than those usually found after overt Japanese encephalitis. Contrariwise CF antibody did not display a difference in maximal titers. Neutralizing, CF and HI antibodies persisted at detectable levels in plasma and serum for different periods of time after inapparent infection (neutralizing for many years, CF for at least 5–6 weeks but less than 9 months, and HI for years in many persons.)