日本脳炎ウイルスSD12-F120株の表現型および遺伝子型の比較

Phenotypic and Genotypic Comparison of a Live-Attenuated Genotype I Japanese Encephalitis Virus SD12-F120 Strain with Its Virulent Parental SD12 Strain.

• Muhammad Naveed Anwar
• Xin Wang
• Muddassar Hameed
• Abdul Wahaab
• Chenxi Li
• Mona Sharma
• Linlin Pang
• Muhammad Irfan Malik
• Ke Liu
• Beibei Li
• Yafeng Qiu
• Jianchao Wei
• Zhiyong Ma

抄録

日本脳炎ウイルス（JEV）の生きたまま減衰した遺伝子型I（GI）株（SD12-F120）の表現型および遺伝子型特性を，毒性を有する親株SD12株と比較し，減衰過程で獲得した遺伝的変化を明らかにした．SD12-F120株は、SD12株に比べてBHK-21細胞上に小さなプラークを形成し、マウスの脳内での複製の減少を示した。SD12-F120を腹腔内または脳内経路で接種したマウスは臨床症状を示さず、神経浸潤性と神経ウイルス性の両方の点で高度に減衰した表現型を示した。SD12-F120はSD12と比較して29のヌクレオチド変異を有しており，そのうち20はサイレントヌクレオチド変異と考えられたが，9は8つのアミノ酸置換を有していた．SD12-F120対SD12対のアミノ酸変異を他の4つの等原性ペアと比較したところ、Eタンパク質のE位置とE位置の変異はそれぞれ4対と3対で確認されたが、残りのアミノ酸変異はそれぞれのペアにほぼ固有の変異であった。これらの観察から、減衰過程で獲得した遺伝的変化は系統特異的なものである可能性が高く、JEVの減衰・ウイルス化に関連するメカニズムは複雑であることが示唆された。

The phenotypic and genotypic characteristics of a live-attenuated genotype I (GI) strain (SD12-F120) of Japanese encephalitis virus (JEV) were compared with its virulent parental SD12 strain to gain an insight into the genetic changes acquired during the attenuation process. SD12-F120 formed smaller plaque on BHK-21 cells and showed reduced replication in mouse brains compared with SD12. Mice inoculated with SD12-F120 via either intraperitoneal or intracerebral route showed no clinical symptoms, indicating a highly attenuated phenotype in terms of both neuroinvasiveness and neurovirulence. SD12-F120 harbored 29 nucleotide variations compared with SD12, of which 20 were considered silent nucleotide mutations, while nine resulted in eight amino acid substitutions. Comparison of the amino acid variations of SD12-F120 vs SD12 pair with those from other four isogenic pairs of the attenuated and their virulent parental strains revealed that the variations at E and E positions of E protein were identified in four and three pairs, respectively, while the remaining amino acid variations were almost unique to their respective strain pairs. These observations suggest that the genetic changes acquired during the attenuation process were likely to be strain-specific and that the mechanisms associated with JEV attenuation/virulence are complicated.