SUMMARYA panel of monoclonal antibodies (MAbs) raised against an Indian strain of Japanese encephalitis (JE) virus was used to map topographically the epitopes on the envelope protein. Two separate clusters of epitopes were revealed. On the basis of reactivity in haemagglutination inhibition (HI), neutralization (NT), passive protection and antibody-dependent plaque enhancement (ADPE) assays with the MAbs, five functional domains (A, B, C, D and E) were delineated. The flavivirus cross-reactive domain for HI (A) was distinct. The JE virus-specific domain for HI (B) was in continuum with those domains representing non-HI JE virus-specific MAbs (C) and flavivirus cross-reactive MAbs (D). Domain E, which mapped close to domain D was represented by two MAbs that reacted with both JE virus and uninfected cell nuclei. Four conclusions can be drawn. (i) Two distinct antigenic domains were associated with HI, (ii) HI and NT in vivo and in vitro were dissociated functions, (iii) ADPE activity was solely linked with the A domain and (iv) all MAbs reacting with epitopes in the B domain had HI/NT/protective activity but failed to show ADPE. The B domain might therefore be considered the most suitable for development of synthetic or genetically engineered vaccines.

Japanese encephalitis (JE) virus replicated in monkey, pig and day-old chick leucocyte cultures. The titres obtained on days 3 to 5 after infection in monkey, pig and chick leucocyte cultures were comparable. Treatment of monkey leucocyte cultures with the mitogens phytohaemagglutinin P, pokeweed mitogen (PWM), formalinized Staphylococcus aureus (Cowan I) or concanavalin A and pig leucocytes with PWM did not significantly affect their ability to support replication of JE virus. No relationship was observed between the amount of [3H]thymidine incorporated in untreated or mitogen treated monkey or pig leucocyte cultures and the titres of JE virus in such cultures. The ability of monkey, pig and chick leucocyte cultures to support JE virus replication was abrogated following silica treatment. These findings suggest that monocytes may serve as one of the important sites of JE virus replication.

A comparative study of interferon (IFN) production (type-alpha and gamma) was carried out using Ficoll-hypaque purified fresh and cryopreserved mononuclear cells from eight normal healthy individuals. Newcastle disease virus-NDV (R2B strain) was used as an inducer for type-alpha and Staphylococcal enterotoxin-A-(SEA) for type-gamma IFN production. There was no significant difference between the titres of type-alpha and gamma-IFN and lymphocyte subpopulations of fresh and cryopreserved mononuclear cells studied under identical conditions.