Discipline of Infectious Diseases and Immunology, The University of Sydney, Camperdown, New South Wales, Australia.
Discipline of Infectious Diseases and Immunology, The University of Sydney, Camperdown, New South Wales, Australia
J Virol. 2019 Oct 29;93(22). doi: 10.1128/JVI.01140-19. Print 2019 Nov 15.
Immune regulation of alphaherpesvirus latency and reactivation is critical for the control of virus pathogenesis. This is evident for herpes simplex virus 1 (HSV-1), where cytotoxic T lymphocytes (CTLs) prevent viral reactivation independent of apoptosis induction. This inhibition of HSV-1 reactivation has been attributed to granzyme B cleavage of HSV infected cell protein 4 (ICP4); however, it is unknown whether granzyme B cleavage of ICP4 can directly protect cells from CTL cytotoxicity. Varicella zoster virus (VZV) is closely related to HSV-1; however, it is unknown whether VZV proteins contain granzyme B cleavage sites. Natural killer (NK) cells play a central role in VZV and HSV-1 pathogenesis and, like CTLs, utilize granzyme B to kill virally infected target cells. However, whether alphaherpesvirus granzyme B cleavage sites could modulate NK cell-mediated cytotoxicity has yet to be established. This study aimed to identify novel HSV-1 and VZV gene products with granzyme B cleavage sites and assess whether they could protect cells from NK cell-mediated cytotoxicity. We have demonstrated that HSV ICP27, VZV open reading frame 62 (ORF62), and VZV ORF4 are cleaved by granzyme B. However, in an NK cell cytotoxicity assay, only VZV ORF4 conferred protection from NK cell-mediated cytotoxicity. The granzyme B cleavage site in ORF4 was identified via site-directed mutagenesis and, surprisingly, the mutation of this cleavage site did not alter the ability of ORF4 to modulate NK cell cytotoxicity, suggesting that ORF4 has a novel immunoevasive function that is independent from the granzyme B cleavage site. HSV-1 causes oral and genital herpes and establishes life-long latency in sensory ganglia. HSV-1 reactivates multiple times in a person's life and can cause life-threatening disease in immunocompromised patients. VZV is closely related to HSV-1, causes chickenpox during primary infection, and establishes life-long latency in ganglia, from where it can reactivate to cause herpes zoster (shingles). Unlike HSV-1, VZV only infects humans, and there are limited model systems; thus, little is known concerning how VZV maintains latency and why VZV reactivates. Through studying the link between immune cell cytotoxic functions, granzyme B, and viral gene products, an increased understanding of viral pathogenesis will be achieved.
α疱疹病毒潜伏和再激活的免疫调控对于控制病毒发病机制至关重要。单纯疱疹病毒 1（HSV-1）就是一个明显的例子，其中细胞毒性 T 淋巴细胞（CTL）在不诱导细胞凋亡的情况下阻止病毒再激活。这种对 HSV-1 再激活的抑制归因于颗粒酶 B 对 HSV 感染细胞蛋白 4（ICP4）的切割；然而，颗粒酶 B 对 ICP4 的切割是否能直接保护细胞免受 CTL 的细胞毒性尚不清楚。水痘带状疱疹病毒（VZV）与 HSV-1 密切相关；然而，尚不清楚 VZV 蛋白是否含有颗粒酶 B 切割位点。自然杀伤（NK）细胞在 VZV 和 HSV-1 的发病机制中起着核心作用，与 CTL 一样，它们利用颗粒酶 B 杀死病毒感染的靶细胞。然而，α疱疹病毒颗粒酶 B 切割位点是否能调节 NK 细胞介导的细胞毒性尚未确定。本研究旨在鉴定具有颗粒酶 B 切割位点的新型 HSV-1 和 VZV 基因产物，并评估它们是否能保护细胞免受 NK 细胞介导的细胞毒性。我们已经证明，HSV ICP27、VZV 开放阅读框 62（ORF62）和 VZV ORF4 可被颗粒酶 B 切割。然而，在 NK 细胞细胞毒性测定中，只有 VZV ORF4 赋予了对 NK 细胞介导的细胞毒性的保护作用。ORF4 中的颗粒酶 B 切割位点是通过定点突变鉴定的，令人惊讶的是，该切割位点的突变并没有改变 ORF4 调节 NK 细胞细胞毒性的能力，这表明 ORF4 具有一种独立于颗粒酶 B 切割位点的新型免疫逃避功能。HSV-1 引起口腔和生殖器疱疹，并在感觉神经节中建立终身潜伏。HSV-1 在一个人的一生中多次复发，并可在免疫功能低下的患者中引起危及生命的疾病。VZV 与 HSV-1 密切相关，在初次感染时引起水痘，并在神经节中建立终身潜伏，从那里它可以重新激活引起带状疱疹（带状疱疹）。与 HSV-1 不同，VZV 仅感染人类，并且模型系统有限；因此，对于 VZV 如何维持潜伏以及为什么 VZV 会重新激活，人们知之甚少。通过研究免疫细胞细胞毒性功能、颗粒酶 B 和病毒基因产物之间的联系，将增进对病毒发病机制的理解。
