Lomniczi B, Kaplan A S, Ben-Porat T
Veterinary Medical Research Institute, Hungarian Academy of Sciences, Budapest.
Virology. 1987 Nov;161(1):181-9. doi: 10.1016/0042-6822(87)90184-x.
Several independently isolated vaccine strains of pseudorabies virus were studied to identify the functions that play a role in the expression of virulence of this virus. All the strains that were studied grew well in three different cell types. No differences that could be correlated with avirulence could be detected either in the virus yield produced by the cells or in the length of the eclipse phases. All the attenuated strains, however, had lost their ability to replicate efficiently in the brains of day-old chickens. The defects leading to the decrease in the virulence for day-old chickens varied in the different vaccine strains. The Tatarov vaccine strain is defective in the thymidine kinase (TK) gene; restoration of a functional TK gene restores to this strain its virulence for day-old chickens and for pigs. Three out of four different, independently isolated avirulent strains were found to be defective in different loci, as determined by their ability to generate virulent recombinants. Two strains, Bartha and Buk Z300, however, yielded few virulent recombinants, indicating that they were defective in at least one closely linked function. Furthermore, all the virulent recombinants obtained from cells coinfected with different pairwise combinations of the vaccine strains had higher LD50 values than virulent wild-type virus, indicating that the recombinants had not acquired all the functions necessary for optimum expression of virulence. Partial virulence was also restored to Buk Z900 by marker rescue with sequences originating from three different regions of the wild-type pseudorabies virus genome. All three of these regions were different from those that had previously been shown to rescue virulence of the Bartha strain (B. Lomniczi, S. Watanabe, T. Ben-Porat, and A. S. Kaplan, 1987, J. Virol. 61, 796-801). Our results thus show that (1) defects in several different loci of the pseudorabies virus genome can affect virulence without detectably affecting growth in cell culture and (2) most vaccine strains have multiple defects contributing to their lack of virulence.
对几种独立分离的伪狂犬病病毒疫苗株进行了研究，以确定在该病毒毒力表达中起作用的功能。所有研究的毒株在三种不同的细胞类型中生长良好。在细胞产生的病毒产量或隐蔽期的长度方面，均未检测到与无毒力相关的差异。然而，所有减毒株都失去了在一日龄雏鸡脑中高效复制的能力。导致对一日龄雏鸡毒力降低的缺陷在不同的疫苗株中各不相同。塔塔罗夫疫苗株的胸苷激酶（TK）基因存在缺陷；功能性TK基因的恢复使该毒株恢复了对一日龄雏鸡和猪的毒力。通过产生有活力重组体的能力确定，在四个不同的、独立分离的无毒力毒株中，有三个在不同位点存在缺陷。然而，两种毒株，即巴塔毒株和布克Z300毒株，产生的有活力重组体很少，这表明它们在至少一种紧密连锁的功能上存在缺陷。此外，从用疫苗株的不同两两组合共同感染的细胞中获得的所有有活力重组体的半数致死剂量（LD50）值均高于有活力的野生型病毒，这表明重组体并未获得毒力最佳表达所需的所有功能。通过用源自野生型伪狂犬病病毒基因组三个不同区域的序列进行标记拯救，布克Z900毒株的部分毒力也得以恢复。这三个区域均不同于先前已证明可拯救巴塔毒株毒力的区域（B. 洛姆尼茨、S. 渡边、T. 本 - 波拉特和A. S. 卡普兰，1987年，《病毒学杂志》61卷，796 - 801页）。因此，我们的结果表明：（1）伪狂犬病病毒基因组几个不同位点的缺陷可影响毒力，而在细胞培养中生长未受明显影响；（2）大多数疫苗株存在多种缺陷，导致其缺乏毒力。
