Serological Studies of Japanese Encephalitis

Hemagglutination-inhibiting, Compleinentfixing and Neutralizing Antibody Response in Patients with Japanese Encephalitis

Abstract

Tests of hemagglutination-inhibition (HI), complement-fixation (CF) and neutralization (NT) against the NAKAYAMA-RFVL strain of Japanese encephalitis virus were carried out on 169 patients affected with Japanese encephalitis during acute illness and convalescence between 1962 and 1966.
1) LLC-MK2, a stable cell line established by Hull et al., from a rhesus monkey kidney was used for the NT test. The NT antibodies were assayed in the monolayer cultures based on inhibition of cytopathic effect by the constant varying serum technique. The antigen was the infected supernatant fluid, which was started from the suspension of infected suckling mice brains and then serial passage in the cells was carried out at least twelve times. The amount of infectious virus present in the cultured fluids, was estimated to be between 10-^6.50 TCD50/ml and 10-^6.75 TCD50/ml. The titers of NT antibody estimated by this method were approximately equivalent to those by the intra-cercbral test in mice.
2) All 159 cases which could be followed up through convalescence showed a clear-cut rise of antibody titer in all of HI, CF and NT tests against the Nakayama antigen. It was the longest observed case; bleeding occurred for 563 days.
3) More than half of the cases possesed the HI antibody within the first few days of disease, and in all cases the antibody was detectable within the first week. The antibody reached the maximum titer in 62.9% of all cases by the 14th day of illness and in 96.9% of those by the 28th day. The maximum titer was 1: 160 or more in 89.9% of those and 1: 640 or more in 42.1%. The HI antibody was detectable with one exception in 41 cases which were followed up over a six month period.
4) The CF antibody was not detectable within the first few days of disease in more than half of the cases but appeared within the 14th day in all cases with one exception. The antibody reached the maximum titer in 48.4% of all cases by the 14th day and in 82.4% of those by the 28th day. The maximum titer was 1: 16 or more in 92.5% of the cases and 1: 64 or more in 61.0%. In 40 cases which were observed over a six month period, the CF antibody was detectable in 80% of the cases but not detectable in 20%.
5) In more than half of the cases the NT antibody appeared within the first few days of illness and in all cases developed within the 8th day. The antibody reached the maximum titer by the 14th day in 62.9% of all cases and in 97.5% of those by the 28th day. The maximum titer was 1: 16 or more in 95.0% of the cases and 1: 16 or more in 43.4%. The NT antibody was demonstrated at a significant level in all 41 cases which were followed up over a six month period.
6) The HI and NT antibodies appeared and reached the maximum titer simultaneously but the appearance and peak of CF antibody was slightly delayed as compared with the HI and NT antibodies. In most of the cases in which all the antibodies of three sorts were detectable, a tenth of the HI antibody titer was nearly equivalent to the CF and NT antibody titers. With respect to changes in antibody titer the following tendencies were noted: the CF antibody tended to decrease rapidly, the HI antibody decreased, and the NT antibody persisted over a long period at a conspiciously detectable level.
7) In many of affected individuals aged 50 or more these antibodies elevated significantly. However, it should be borne in mind that the cases responded at a barely detectable level also belonged to this age group.
8) In 17 of 169 cases who had received vaccination, the antibodies tended to elevate more rapidly, the maximum titer being higher than others.
9) Among 59 cases in which Japanese encephalitis was ruled out serologically and clinically, the NT antibody was demonstrated in 22 cases and both the HI and NT antibodies in 16 cases but the CF antibody was not detectable in any cases.