为了解乙脑减毒活疫苗株SA14—14—2的神经毒力减毒机制，用RT—PCR方法分别扩增不同减毒程度毒株的E 基因，克隆、测序，继而对各毒株序列进行比较。结果表明SA14强毒株与SA 12—1—7株间只有3个氨基酸发生改 变(E-107，E一176，E一439)，SA l2一l一7与SA14—9—7和SA14—5—3株间有另3个氨基酸发生改变(E一138，E一279，E一315)。 SA 9—7株与SA】4—5—3株只有一个核苷酸NT一405不同，但未引起氨基酸改变。SAl4—14—2疫苗株除保留SA14—12— 1—7和SA 9—7所改变的6个氨基酸外，另有2个氨基酸发生了改变(E一177，E一264)，共计在E区共发生8个氨基 酸的替代。SA 12—1—7株的低神经毒力很不稳定而其余各株的弱毒特征很稳定。因此，E-176(I1e— Va1)，E-439 (Lys一 g)和E一107(Leu--~Phe)可能与神经外和神经内毒力减弱有关。E一138(Gu1一Lys)，E一315(AJa— Va1)和E一 279(Lys— Met)的突变可能与神经毒力的减弱和稳定性相关。

For understanding the mechanism Of neurovirulence attenuation Of the Japanese encephalitis virus(JEV)，nucleotides of the E coding region of five JE strains，one wild and four attenuated viruses， were am plified by PCR and sequenced．A comparison of the five sequences indicated that there were tO— tally twelve nucleotides and eight amino acid differences between the vaccine strain SA14—14—2(PHK一8) and its parent SA14，in which three amino acids(E一107，E一176，E一439)were different between SA14 and SA14-12—1—7，and other three amino acids(E一138，E一279，E一315)were different between SAx4-12— 1—7 and SA14-9—7 as well as SA14-5—3．The SA14-12—1—7 strain showed low neurovirulence but unstable， whereas al1 the other attenuated strains showed high stability of attenuation．Our results suggest that the mutations of E一176(I1e Va1)，E一439(Lys Arg)and E一107(Leu-+Phe)may contribute for the attenuation of neuroinvasion and neurovirulence and the m utations of E一1 38，E一279，E一3 1 5 may con— tribute tO the attenuation of the neuroviru1ence and itS stability