鼠γ疱疹病毒68(MHV68):研究γ疱疹病毒感染的模型

γ疱疹病毒成员遍及自然界,可感染包括人在内的多种哺乳动物.γ疱疹病毒的生物学特性主要有:(1)能在淋巴细胞中潜伏感染;(2)可以产生淋巴增生性疾病;(3)与淋巴组织和非淋巴组织肿瘤关系密切.最开始γ疱疹病毒根据感染T或B细胞的不同而分为γ1和γ2疱疹病毒,前者主要感染B淋巴细胞,如感染人和棉顶绒猴的EBV(EpsteinBarr virus);γ2疱疹病毒则感染T淋巴细胞,以感染松鼠猴的疱疹病毒samiri(herpesvirus samiri,HVS)为代表.但后来证实γ2疱疹病毒可同时感染T、B淋巴细胞,而EBV亦可引起T淋巴细胞肿瘤.因此以后发现的γ疱疹病毒则根据其基因结构及基因组中代表性序列的特点,将其归为γ1或γ2亚类.如感染人的卡波氏肉瘤相关病毒(Kaposi's sarcomaassociated herpesvirus,KSHV)或称人疱疹病毒8(human herpesvirus-8,HHV8)就归为γ2[1].     

Murine Gammaherpesvirus 68 Encodes a Second PML-Modifying Protein

The ORF75c tegument protein of murine gammaherpesvirus 68 (MHV68) promotes the degradation of the antiviral promyelocytic leukemia (PML) protein. Surprisingly, MHV68 expressing a degradation-deficient ORF75c replicated in cell culture and in mice similar to the wild-type virus. However, in cells infected with this mutant virus, PML formed novel track-like structures that are induced by ORF61, the viral ribonucleotide reductase large subunit. These findings may explain why ORF75c mutant viruses unable to degrade PML had no demonstrable phenotype after infection.     

Turnover of T Cells in Murine Gammaherpesvirus 68-Infected Mice

Respiratory challenge of C57BL/6 mice with murine gammaherpesvirus 68 induces proliferation of T lymphocytes early after infection, as evidenced by incorporation of the DNA precursor bromodeoxyuridine. Using pulse-chase analysis, splenic and peripheral blood activated T lymphocytes were found to continue dividing for at least a month after the initial virus challenge. The results are in accord with the idea that T cells are stimulated for a substantial time after the acute, lytic phase of virus infection is resolved.     

Zinc Finger Antiviral Protein Inhibits Murine Gammaherpesvirus 68 M2 Expression and Regulates Viral Latency in Cultured Cells

Zinc finger antiviral protein (ZAP) is a host factor that specifically inhibits the replication of certain viruses by binding to specific viral mRNAs and repressing mRNA expression. Here we report that ZAP inhibits expression of murine gammaherpesvirus 68 (MHV-68) M2, which plays important roles in establishment and maintenance of viral latency. Downregulation of endogenous ZAP in cells harboring latent MHV-68 promoted lytic replication of the virus. These results suggest that ZAP inhibits M2 expression and regulates the maintenance of MHV-68 latency.     

Signaling through Toll-Like Receptors Induces Murine Gammaherpesvirus 68 Reactivation In Vivo

Murine gammaherpesvirus 68 (MHV68) establishes a lifelong infection in mice and is used as a model pathogen to study the role of viral and host factors in chronic infection. The maintenance of chronic MHV68 infection, at least in some latency reservoirs, appears to be dependent on the capacity of the virus to reactivate from latency in vivo. However, the signals that lead to MHV68 reactivation in vivo are not well characterized. Toll-like receptors (TLRs), by recognizing the specific patterns of microbial components, play an essential role in the activation of innate immunity. In the present study, we investigated the capacity of TLR ligands to induce MHV68 reactivation, both in vitro and in vivo. The stimulation of latently infected B cell lines with ligands for TLRs 3, 4, 5, and 9 enhanced MHV68 reactivation; the ex vivo stimulation of latently infected primary splenocytes, recovered from infected mice, with poly(I:C), lipopolysaccharide, flagellin, or CpG DNA led to early B-cell activation, B-cell proliferation, and a significant increase in the frequency of latently infected cells reactivating the virus. In vivo TLR stimulation also induced B-cell activation and MHV68 reactivation, resulting in heightened levels of virus replication in the lungs which correlated with an increase in MHV68-specific CD8⁺ T-cell responses. Importantly, TLR stimulation also led to an increase in MHV68 latency, as evidenced by an increase in viral genome-positive cells 2 weeks post-in vivo stimulation by specific TLR ligands. Thus, these data demonstrate that TLR stimulation can drive MHV68 reactivation from latency and suggests that periodic pathogen exposure may contribute to the homeostatic maintenance of chronic gammaherpesvirus infection through stimulating virus reactivation and reseeding latency reservoirs.