Schickli J H, Wentworth D E, Zelus B D, Holmes K V, Sawicki S G
Department of Microbiology, University of Colorado Health Sciences Center, Denver 80262, USA.
Adv Exp Med Biol. 1998;440:735-41. doi: 10.1007/978-1-4615-5331-1_95.
Murine coronavirus MHV-A59 normally infects only murine cells in vitro and causes transmissible infection only in mice. In the 17 C1 1 line of murine cells, the receptor for MHV-A59 is MHVR, a biliary glycoprotein in the carcinoembryonic antigen (CEA) family of glycoproteins. We found that virus released from the 600th passage of 17 C1 1 cells persistently infected with MHV-A59 (MHV/pi600) replicated in hamster (BHK-21) cells. The virus was passaged and plaque-purified in BHK-21 cells, yielding the MHV/BHK strain. Because murine cells persistently infected with MHV-A59 express a markedly reduced level of MHVR (Sawicki, et al., 1995), we tested whether virus with altered receptor interactions was selected in the persistently infected culture. Infection of 17 C1 1 cells by MHV-A59 can be blocked by treating the cells with anti-MHVR MAb-CC1, while infection by MHV/BHK was only partially blocked by MAb-CC1. MHV/BHK virus was also more resistant than wild-type MHV-A59 to neutralization by purified, recombinant, soluble MHVR glycoprotein (sMHVR). Cells in the persistently infected culture may also express reduced levels of and have altered interactions with some of the Bgp-related glycoproteins that can serve as alternative receptors for MHV-A59. Unlike the parental MHV-A59 which only infects murine cells, MHV/BHK virus was able to infect cell lines derived from mice, hamsters, rats, cats, cows, monkeys and humans. However, MHV/BHK was not able to infect all mammalian species, because a pig (ST) cell line and a dog cell line (MDCK I) were not susceptible to infection. MHV/pi600 and MHV/BHK replicated in murine cells more slowly than MHV-A59 and formed smaller plaques. Thus, in the persistently infected murine cells which expressed a markedly reduced level of MHVR, virus variants were selected that have altered interactions with MHVR and an extended host range. In vivo, in mice infected with coronavirus, virus variants with altered receptor recognition and extended host range might be selected in tissues that have low levels of receptors. Depending upon the tissue in which such a virus variant was selected, it might be shed from the infected animal or eaten by a predator, thus presenting a possible means for initiating the transition of a variant virus into a new host as a model for an emerging virus disease.
鼠冠状病毒MHV - A59通常仅在体外感染鼠细胞，且仅在小鼠中引起可传播的感染。在鼠细胞的17 C1 1系中，MHV - A59的受体是MHVR，它是癌胚抗原（CEA）糖蛋白家族中的一种胆汁糖蛋白。我们发现，从持续感染MHV - A59的17 C1 1细胞第600代释放的病毒（MHV/pi600）能在仓鼠（BHK - 21）细胞中复制。该病毒在BHK - 21细胞中传代并进行空斑纯化，产生了MHV/BHK毒株。由于持续感染MHV - A59的鼠细胞表达的MHVR水平显著降低（Sawicki等人，1995年），我们测试了在持续感染培养物中是否选择了具有改变的受体相互作用的病毒。用抗MHVR单克隆抗体CC1处理细胞可阻断MHV - A59对17 C1 1细胞的感染，而MAb - CC1仅部分阻断MHV/BHK的感染。MHV/BHK病毒对纯化的重组可溶性MHVR糖蛋白（sMHVR）的中和作用也比野生型MHV - A59更具抗性。持续感染培养物中的细胞可能还会表达降低水平的某些Bgp相关糖蛋白，并且与这些可作为MHV - A59替代受体的糖蛋白的相互作用也发生了改变。与仅感染鼠细胞的亲本MHV - A59不同，MHV/BHK病毒能够感染源自小鼠、仓鼠、大鼠、猫、牛、猴和人的细胞系。然而，MHV/BHK不能感染所有哺乳动物物种，因为猪（ST）细胞系和犬细胞系（MDCK I）对感染不敏感。MHV/pi600和MHV/BHK在鼠细胞中的复制速度比MHV - A59慢，形成的空斑也更小。因此，在表达显著降低水平MHVR的持续感染鼠细胞中，选择出了与MHVR相互作用改变且宿主范围扩大的病毒变体。在体内，感染冠状病毒的小鼠中，在受体水平较低的组织中可能会选择出受体识别改变且宿主范围扩大的病毒变体。根据选择出这种病毒变体的组织不同，它可能会从感染动物体内排出或被捕食者吃掉，从而为新兴病毒病模型中变异病毒向新宿主的转变提供了一种可能的途径。
