Morley Peter J, Ertl Peter, Sweet Clive
UK Virology Department, GlaxoSmithKline Research and Development Ltd., United Kingdom.
J Med Virol. 2002 Jun;67(2):187-99. doi: 10.1002/jmv.2207.
Previously, we showed that two temperature-sensitive mutants of murine cytomegalovirus (tsm5 and tsm30) expressed immediate-early (IE-1), early (E-1), and late (gB) phase genes in the tissues of immunocompetent Balb/c mice, yet failed to produce infectious progeny virus in any tissue at any time at 1-21 days post-infection. Mice inoculated intraperitoneally with tsm5 became latently infected, but this latent virus could not be reactivated as an infectious virus after immunosuppression, although all three transcripts were produced. Immunocompetent mice infected with tsm30 did not become latently infected. In the present study, immunodeficient SCID mice supported productive infection of both mutants, suggesting that low-level viral replication does occur in immunocompetent mice, but that it is limited by the host immune response. This is supported by the observation that immunocompetent mice were protected against virulent K181 challenge even after immunisation with as few as 40 pfu of mutant virus, whereas UV-inactivated mutant or K181 virus was not immunoprotective at doses of 40,000 pfu. Immunity induced by subcutaneous inoculation was also protective, whereas that induced by intragastric immunisation was not. Protection was lifelong (18 months). Although tsm5 induced high antibody titres, there was little evidence of an antibody response to tsm30. In contrast, a significant CD8(+) CTL response to the Balb/c immunodominant IE-1 nonapeptide (YPHFMPTNL) was elicited by both mutants, as determined by an interferon-gamma ELISPOT assay, although this response was lower than that induced by K181 infection. In addition, CTLs specific for m04 (YGPSLYRRF) and M84 (AYAGLFTPL) peptides could be detected at low frequency after K181, tsm5, and tsm30 immunisation. Such protective immunity did not prevent the challenge K181 virus from entering the latent state, but it appeared to reduce the frequency of reactivation.
此前，我们发现鼠巨细胞病毒的两个温度敏感突变株（tsm5和tsm30）在免疫功能正常的Balb/c小鼠组织中可表达即刻早期（IE-1）、早期（E-1）和晚期（gB）阶段基因，但在感染后1至21天的任何时间，均无法在任何组织中产生有感染性的子代病毒。腹腔接种tsm5的小鼠发生潜伏感染，但尽管产生了所有三种转录本，这种潜伏病毒在免疫抑制后仍无法重新激活为有感染性的病毒。感染tsm30的免疫功能正常小鼠未发生潜伏感染。在本研究中，免疫缺陷的SCID小鼠支持这两种突变株的增殖性感染，这表明免疫功能正常的小鼠中确实发生了低水平的病毒复制，但受到宿主免疫反应的限制。这一观点得到了以下观察结果的支持：即使只用少至40 pfu的突变病毒免疫，免疫功能正常的小鼠也能抵抗强毒株K181的攻击，而紫外线灭活的突变病毒或K181病毒在40,000 pfu剂量时并无免疫保护作用。皮下接种诱导的免疫也具有保护作用，而胃内免疫诱导的免疫则不然。保护作用是终身的（18个月）。尽管tsm5诱导了高抗体滴度，但几乎没有证据表明存在针对tsm30的抗体反应。相比之下，通过干扰素-γ ELISPOT试验确定，两种突变株均引发了针对Balb/c免疫显性IE-1九肽（YPHFMPTNL）的显著CD8(+) CTL反应，尽管这种反应低于K181感染诱导的反应。此外，在K181、tsm5和tsm30免疫后，可低频率检测到针对m04（YGPSLYRRF）和M84（AYAGLFTPL）肽的CTL。这种保护性免疫并不能阻止攻击的K181病毒进入潜伏状态，但似乎降低了重新激活的频率。
