Panda Aruna, Huang Zhuhui, Elankumaran Subbiah, Rockemann Daniel D, Samal Siba K
Virginia-Maryland Regional College of Veterinary Medicine, University of Maryland, 8075 Greenmead Drive, College Park, MD 20742, USA.
Microb Pathog. 2004 Jan;36(1):1-10. doi: 10.1016/j.micpath.2003.07.003.
Newcastle disease virus (NDV) causes a highly contagious and economically important disease in poultry. Viral determinants of NDV virulence are not completely understood. The amino acid sequence at the protease cleavage site of the fusion (F) protein has been postulated as a major determinant of NDV virulence. In this study, we have examined the role of F protein cleavage site sequence in NDV virulence using reverse genetics technology. The sequence G-R-Q-G-R present at the cleavage site of the F protein of avirulent strain LaSota was mutated to R-R-Q-K-R, which is present in the F cleavage site of neurovirulent strain Beaudette C (BC). The resultant mutated LaSota V.F. virus did not require exogenous protease for infectivity in cell culture, indicating that the F protein was cleaved by intracellular proteases. The virulence of the mutant and parental viruses was evaluated in vivo by intracerebral pathogenicity index (ICPI) and intravenous pathogenicity index (IVPI) tests in chickens. Our results showed that the modification of the F protein cleavage site resulted in a dramatic increase in virulence from an ICPI value of 0.00 for LaSota to a value of 1.12 for LaSota V.F. However, the ICPI value of LaSota V.F. was lower than that of BC, which had a value of 1.58. Interestingly, the IVPI tests showed values of 0.00 for both LaSota and LaSota V.F. viruses, compared to the IVPI value of 1.45 of BC. In vitro characteristics of the viruses were also studied. Our results demonstrate that the efficiency of cleavage of the F protein plays an important role if the NDV is delivered directly into the brains of chicks, but there could be other viral factors that probably affect peripheral replication, viremia, or entry into the central nervous system.
新城疫病毒（NDV）可在家禽中引发一种具有高度传染性且在经济上十分重要的疾病。人们对NDV毒力的病毒决定因素尚未完全了解。融合（F）蛋白蛋白酶切割位点的氨基酸序列被认为是NDV毒力的主要决定因素。在本研究中，我们利用反向遗传学技术研究了F蛋白切割位点序列在NDV毒力中的作用。无毒力的LaSota株F蛋白切割位点处的序列G-R-Q-G-R突变为神经毒力的Beaudette C（BC）株F切割位点处的R-R-Q-K-R。所得的突变型LaSota V.F.病毒在细胞培养中感染性无需外源性蛋白酶，这表明F蛋白可被细胞内蛋白酶切割。通过对鸡进行脑内致病性指数（ICPI）和静脉致病性指数（IVPI）试验，在体内评估了突变病毒和亲本病毒的毒力。我们的结果表明，F蛋白切割位点的修饰导致毒力显著增加，LaSota的ICPI值为0.00，而LaSota V.F.的ICPI值为1.12。然而，LaSota V.F.的ICPI值低于BC株，BC株的ICPI值为1.58。有趣的是，IVPI试验显示LaSota和LaSota V.F.病毒的值均为0.00，而BC株的IVPI值为1.45。还研究了病毒的体外特性。我们的结果表明，如果将NDV直接接种到雏鸡脑中，F蛋白的切割效率起着重要作用，但可能还有其他病毒因素影响外周复制、病毒血症或进入中枢神经系统。
