Experimental Analysis of Pathogenicity of Cytomegalovirus with The Attenuated Mutants.

人巨细胞病毒(HCMV)在器官移植受者和获得性免疫缺陷综合征(AIDS)患者等免疫功能低下的宿主中引起先天性感染和严重疾病。由于巨细胞病毒的种属特异性，其感染机制和致病机制已被动物模型所研究。我们采用小鼠巨细胞病毒(MCMV)作为巨细胞病毒的模型，从Smith株(野生型；wt)中分离到温度敏感的MCMV突变株，以获得致病性降低的突变株。其中一种菌株ts21在39ﾟC时缺乏合成dna的能力，并显示出在新生小鼠中引起致命感染的能力降低。将ts21与wt回交，产生了对温度不敏感但对小鼠仍有减毒作用的重组(Rec21w)。这些结果表明TS21含有两个独立的突变：一个突变(S)负责温度敏感性(Ts)，一个突变(S)负责衰减(…)更多的ATT)。这些突变株的基因类型分别为ts21(ts，att)和rec21w(ts^+，att)，并研究了各突变对病毒体内复制和致病力的影响。Wt和rec21w之间的遗传差异存在于ATT基因。感染rec21w的小鼠的靶器官病毒滴度与wt感染的小鼠几乎相同，但rec21w对器官的损伤和腹腔出血比wt少，从而降低了MCMV诱导临床病理变化的能力，而不影响靶器官的复制能力。因此，巨细胞病毒的致死性感染需要一个能引起临床病理变化的因素(S)。Rec21w和ts21在ts基因上存在遗传差异。TS21在感染小鼠的器官中复制几乎完全受限，而在感染TS21的小鼠的器官中几乎没有观察到临床病理变化。体内外研究结果表明，Ts21是一种温度敏感突变(S)，发生在细胞内病毒复制所必需的基因(S)上，其致病性降低直接归因于靶器官缺乏病毒复制，而靶器官的温度不允许病毒生长。较少

Human cytomegalovirus (HCMV) causes congenital infections and serious diseases in immunocompromised hosts including organ transplant recipients and patients with acquired immunodeficiency syndrome (AIDS). Because of species-specificity, mechanisms of infection and pathogenesis of HCMV has been studied with animal models. We employed murine cytomegalovirus (MCMV) as a model for HCMV.Temperature-sensitive mutants of MCMV were isolated from the Smith strain (wild type; wt) for the purpose of obtaining mutant strains with reduced pathogenicity. One of them, ts21, lacks the ability to synthesize DNA at 39ﾟC and showed the reduced ability to cause lethal infection in newborn mice. Back cross of ts21 with wt resulted in production of a recombinant (rec21w) which were temperature-insensitive but still attenuated for mice. These results suggest that ts21 harbors two independent mutations: a mutation(s) responsible for temperature sensitivity (ts), and a mutation(s) responsible for attenuation ( … More att). Genotypes of these mutants were proposed as follows: ts21 (ts, att), and rec21w (ts^+, att).The effect of each mutation on in vivo virus replication and pathogenicity was investigated. A genetical difference between wt and rec21w exists in the att gene. Virus titer in the target organs of rec21w-infected mice was almost as same as that of wt-infected mice, but rec21w produced less organ damage and less intraperitoneal hemorrhage than wt. Thus att reduces the capacity of MCMV to induce clinicopathological changes without affecting the capacity to replicate in the target organs. Therefore, lethal infection of MCMV requires a factor(s) responsible for clinicopathological changes. A genetical difference between rec21w and ts21 exists in the ts gene. Replication of ts21 was almost completely restricted in the organs of infected mice and little clinicopathological change was observed in the organs of ts21-infected rniee. The in vivo and in vitro result suggest that ts is a temperature-sensitive mutation(s) which occurred in a gene(s) essential for virus replication in cells, and the reduced pathogenicity of ts21 is directly attributable to lack of virus multiplication in the target organs whose temperature is nonpermissive for virus growth. Less