Lawler Clara, de Miranda Marta Pires, May Janet, Wyer Orry, Simas J Pedro, Stevenson Philip G
School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, Australia.
Instituto de Medicina Molecular, Universidade de Lisboa, Lisbon, Portugal.
J Virol. 2018 Mar 14;92(7). doi: 10.1128/JVI.02199-17. Print 2018 Apr 1.
Gammaherpesviruses infect lymphocytes and cause lymphocytic cancers. Murid herpesvirus-4 (MuHV-4), Epstein-Barr virus, and Kaposi's sarcoma-associated herpesvirus all infect B cells. Latent infection can spread by B cell recirculation and proliferation, but whether this alone achieves systemic infection is unclear. To test the need of MuHV-4 for lytic infection in B cells, we flanked its essential ORF50 lytic transactivator with sites and then infected mice expressing B cell-specific Cre (CD19-Cre). The floxed virus replicated normally in Cre mice. In CD19-Cre mice, nasal and lymph node infections were maintained; but there was little splenomegaly, and splenic virus loads remained low. Cre-mediated removal of other essential lytic genes gave a similar phenotype. CD19-Cre spleen infection by intraperitoneal virus was also impaired. Therefore, MuHV-4 had to emerge lytically from B cells to colonize the spleen. An important role for B cell lytic infection in host colonization is consistent with the large CD8 T cell responses made to gammaherpesvirus lytic antigens during infectious mononucleosis and suggests that vaccine-induced immunity capable of suppressing B cell lytic infection might reduce long-term virus loads. Gammaherpesviruses cause B cell cancers. Most models of host colonization derive from cell cultures with continuous, virus-driven B cell proliferation. However, vaccines based on these models have worked poorly. To test whether proliferating B cells suffice for host colonization, we inactivated the capacity of MuHV-4, a gammaherpesvirus of mice, to reemerge from B cells. The modified virus was able to colonize a first wave of B cells in lymph nodes but spread poorly to B cells in secondary sites such as the spleen. Consequently, viral loads remained low. These results were consistent with virus-driven B cell proliferation exploiting normal host pathways and thus having to transfer lytically to new B cells for new proliferation. We conclude that viral lytic infection is a potential target to reduce B cell proliferation.
γ疱疹病毒感染淋巴细胞并引发淋巴细胞癌。鼠疱疹病毒4型（MuHV - 4）、爱泼斯坦 - 巴尔病毒和卡波西肉瘤相关疱疹病毒均感染B细胞。潜伏感染可通过B细胞再循环和增殖传播，但仅靠这一点能否实现全身感染尚不清楚。为了测试MuHV - 4在B细胞中进行裂解感染的必要性，我们在其必需的ORF50裂解反式激活因子两侧设置了loxP位点，然后感染表达B细胞特异性Cre（CD19 - Cre）的小鼠。经floxed修饰的病毒在Cre小鼠中正常复制。在CD19 - Cre小鼠中，鼻腔和淋巴结感染得以维持；但脾脏肿大不明显，脾脏病毒载量仍较低。Cre介导的其他必需裂解基因的去除产生了类似的表型。经腹腔注射病毒后，CD19 - Cre小鼠的脾脏感染也受到损害。因此，MuHV - 4必须从B细胞中进行裂解才能在脾脏中定植。B细胞裂解感染在宿主定植中起重要作用，这与传染性单核细胞增多症期间针对γ疱疹病毒裂解抗原产生的大量CD8 T细胞反应一致，表明能够抑制B细胞裂解感染的疫苗诱导免疫可能会降低长期病毒载量。γ疱疹病毒会引发B细胞癌。大多数宿主定植模型源自具有持续病毒驱动的B细胞增殖的细胞培养。然而，基于这些模型的疫苗效果不佳。为了测试增殖的B细胞是否足以实现宿主定植，我们使小鼠γ疱疹病毒MuHV - 4从B细胞中重新出现的能力失活。修饰后的病毒能够在淋巴结中定植第一波B细胞，但向脾脏等二级部位的B细胞传播较差。因此，病毒载量仍然较低。这些结果与病毒驱动的B细胞增殖利用正常宿主途径并因此必须裂解转移到新的B细胞以进行新的增殖一致。我们得出结论，病毒裂解感染是减少B细胞增殖的潜在靶点。
