Key virulence factors responsible for differences in pathogenicity between clinically proven live-attenuated Japanese encephalitis vaccine SA14-14-2 and its pre-attenuated highly virulent parent SA14.

Publisher: Public Library of Science Country of Publication: United States NLM ID: 101238921 Publication Model: eCollection Cited Medium: Internet ISSN: 1553-7374 (Electronic) Linking ISSN: 15537366 NLM ISO Abbreviation: PLoS Pathog Subsets: MEDLINE

Original Publication: San Francisco, CA : Public Library of Science, c2005-

Vaccines, Attenuated*/immunology ; Vaccines, Attenuated*/genetics ; Encephalitis Virus, Japanese*/genetics ; Encephalitis Virus, Japanese*/pathogenicity ; Encephalitis, Japanese*/virology ; Japanese Encephalitis Vaccines*/immunology ; Japanese Encephalitis Vaccines*/genetics ; Virulence Factors*/genetics; Animals ; Mice ; Virulence ; Humans ; Viral Envelope Proteins/genetics ; Viral Envelope Proteins/metabolism ; Virus Replication ; Chlorocebus aethiops

Japanese encephalitis virus (JEV), a neuroinvasive and neurovirulent orthoflavivirus, can be prevented in humans with the SA14-14-2 vaccine, a live-attenuated version derived from the wild-type SA14 strain. To determine the viral factors responsible for the differences in pathogenicity between SA14 and SA14-14-2, we initially established a reverse genetics system that includes a pair of full-length infectious cDNAs for both strains. Using this cDNA pair, we then systematically exchanged genomic regions between SA14 and SA14-14-2 to generate 20 chimeric viruses and evaluated their replication capability in cell culture and their pathogenic potential in mice. Our findings revealed the following: (i) The single envelope (E) protein of SA14-14-2, which contains nine mutations (eight in the ectodomain and one in the stem region), is both necessary and sufficient to render SA14 non-neuroinvasive and non-neurovirulent. (ii) Conversely, the E protein of SA14 alone is necessary for SA14-14-2 to become highly neurovirulent, but it is not sufficient to make it highly neuroinvasive. (iii) The limited neuroinvasiveness of an SA14-14-2 derivative that contains the E gene of SA14 significantly increases (approaching that of the wild-type strain) when two viral nonstructural proteins are replaced by their counterparts from SA14: (a) NS1/1', which has four mutations on the external surface of the core β-ladder domain; and (b) NS2A, which has two mutations in the N-terminal region, including two non-transmembrane α-helices. In line with their roles in viral pathogenicity, the E, NS1/1', and NS2A genes all contribute to the enhanced spread of the virus in cell culture. Collectively, our data reveal for the first time that the E protein of JEV has a dual function: It is the master regulator of viral neurovirulence and also the primary initiator of viral neuroinvasion. After the initial E-mediated neuroinvasion, the NS1/1' and NS2A proteins act as secondary promoters, further amplifying viral neuroinvasiveness.
Competing Interests: The authors have declared that no competing interests exist.
(Copyright: © 2025 Song et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

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0 (Vaccines, Attenuated)
0 (Japanese Encephalitis Vaccines)
0 (Virulence Factors)
0 (Viral Envelope Proteins)

Date Created: 20250108 Date Completed: 20250117 Latest Revision: 20250119

20250119

PMC11741592

10.1371/journal.ppat.1012844

39775684