Abstract
Comparative studies on the biological and pathogenic characteristics of wild-type strains of Japanese encephalitis (JE) virus and their attenuated derivatives were undertaken in the present project. Two envelope (E) protein reactive monoclonal antibodies (MAbs) (V23 and T60) were found to recognize the attenuated JE vaccine strains (SA-14-2-8, SA-14-5-3 and SA-14-14-2/PHK and PDK9) derived by passage in primary hamster kidney (PHK) cells, but not any wild-type strains examined. While five MAbs (K10, K13, K39, K43 and J44)showed the reverse recognition. Thus, vaccine and wild-type specific epitopes were identified on the E protein of JE virus. Wild-type strains Nakayama-original and 826309, but not SA-14 and Beijing-1, were attenuated for adult mice after six or fewer passages in HeLa cells. The attenuated HeLa passaged JE viruses gained the vaccine specific epitope recognized by MAb V23 and lost the wild-type epitope(s) recognized by MAbs K13 and K39. The non-attenuated HeLa cell passaged JE viruses showed no changes in the above epitopes. Thus, studies with two different attenuation processes (PHK and HeLa cells) would suggest that the E protein epitopes of JE virus are associated with the attenuation and virulence of JE virus. Both attenuated and virulent strains of JE virus were found to bind to mouse brain membrane receptor preparations (MRPs). Binding of wild-type, but none of the attenuated, strains to the MRPs was blocked by preincubation of the MRPs with spiperone, an antagonist for the receptors of the neurotransmitters dopamine and 5-hydroxytryptamine, suggesting that wild-type and attenuated strains have different cell receptors in mouse brain neurones. Taken together, it would appear that mutations in the E protein gene play an important role in the attenuation and/or virulence of JE virus. In addition, studies on the attenuated HeLa cell passaged Nakayama-original virus indicate that this virus may have promise as a potential live JE vaccine virus.