Department of Microbiology, School of Medicine, Wakayama Medical University, Wakayama, Japan.
J Virol. 2024 Mar 19;98(3):e0169823. doi: 10.1128/jvi.01698-23. Epub 2024 Feb 15.
Crimean-Congo hemorrhagic fever virus (CCHFV), a tick-borne virus of the genus, persistently infects tick cells. It has been reported to establish persistent infection in non-human primates, but virological analysis has not yet been performed in human cells. Here, we investigated whether and how nairoviruses persistently infect human cells using Hazara orthonairovirus (HAZV), a surrogate model for CCHFV. We established a human cell line that was persistently infected with HAZV. Surprisingly, virions of persistently infected HAZV (HAZVpi) were not observed in the culture supernatants. There were five mutations (mut1, mut2, mut3, mut4, and mut5) in L protein of HAZVpi. Mutations in L protein of HAZVpi contribute to non-detection of virion in the supernatants. Lmut4 was found to cause low viral growth rate, despite its high polymerase activity. The low growth rate was restored by Lmut2, Lmut3, and Lmut5. The polymerase activity of Lmut1 was extremely low, and recombinant HAZV carrying Lmut1 (rHAZV/Lmut1) was not released into the supernatants. However, genomes of rHAZV/Lmut1 were retained in the infected cells. All mutations (Lmut1-5) found in L protein of HAZVpi were required for experimental reproduction of HAZVpi, and only Lmut1 and Lmut4 were insufficient. We demonstrated that point mutations in viral polymerase contribute to the establishment of persistent HAZV infection. Furthermore, innate immunity was found to be suppressed in HAZVpi-infected cells, which also potentially contributes to viral persistence. This is the first presentation of a possible mechanism behind how nairoviruses establish persistent infection in human cells.
We investigated whether and how nairoviruses persistently infect human cells, using Hazara orthonairovirus (HAZV), a surrogate model for Crimean-Congo hemorrhagic fever virus. We established a human cell line that was persistently infected with HAZV. Five mutations were found in L protein of persistently infected HAZV (HAZVpi): mut1, mut2, mut3, mut4, and mut5. Among them, Lmut1 and Lmut4 restricted viral growth by low polymerase activity and low growth rate, respectively, leading to inhibition of viral overgrowth. The restriction of viral growth caused by Lmut1 and Lmut4 was compensated by other mutations, including Lmut2, Lmut3, and Lmut5. Each of the mutations found in L protein of HAZVpi was concluded to cooperatively modulate viral growth, which facilitates the establishment of persistent infection. Suppression of innate immunity also potentially contributes to virus persistence. This is the first presentation of a possible mechanism behind how nairoviruses establish persistent infection in human cells.
克里米亚-刚果出血热病毒（CCHFV）是一种属于蜱传病毒属的病毒，持续感染蜱细胞。据报道，它在非人类灵长类动物中建立了持续性感染，但在人类细胞中尚未进行病毒学分析。在这里，我们使用 Hazara 正粘病毒（HAZV）作为 CCHFV 的替代模型，研究了纳罗病毒是否以及如何持续性感染人类细胞。我们建立了一种持续性感染 HAZV 的人细胞系。令人惊讶的是，在培养上清液中未观察到持续性感染 HAZV 的病毒粒子（HAZVpi）。HAZVpi 的 L 蛋白中有五个突变（mut1、mut2、mut3、mut4 和 mut5）。HAZVpi 的 L 蛋白突变有助于在上清液中检测不到病毒粒子。尽管 Lmut4 的聚合酶活性很高，但它导致病毒生长速度降低。Lmut2、Lmut3 和 Lmut5 恢复了低生长速率。Lmut1 的聚合酶活性极低，携带 Lmut1 的重组 HAZV（rHAZV/Lmut1）未释放到上清液中。然而，rHAZV/Lmut1 的基因组保留在感染的细胞中。在 HAZVpi 的 L 蛋白中发现的所有突变（Lmut1-5）都需要复制实验来重现 HAZVpi，而只有 Lmut1 和 Lmut4 是不够的。我们证明了病毒聚合酶中的点突变有助于 Hazara 正粘病毒建立持续性感染。此外，在 HAZVpi 感染的细胞中发现了先天免疫受到抑制，这也可能有助于病毒的持续存在。这是纳罗病毒如何在人类细胞中建立持续性感染的潜在机制的首次提出。
我们使用 Hazara 正粘病毒（HAZV）作为克里米亚-刚果出血热病毒的替代模型，研究了纳罗病毒是否以及如何持续性感染人类细胞。我们建立了一种持续性感染 HAZV 的人细胞系。在持续性感染 HAZV（HAZVpi）的 L 蛋白中发现了五个突变：mut1、mut2、mut3、mut4 和 mut5。其中，Lmut1 和 Lmut4 通过低聚合酶活性和低生长速率分别限制病毒的生长，从而抑制病毒的过度生长。Lmut1 和 Lmut4 引起的病毒生长限制被其他突变（包括 Lmut2、Lmut3 和 Lmut5）所补偿。HAZVpi 的 L 蛋白中的每个突变都被认为协同调节病毒的生长，从而有助于建立持续性感染。先天免疫的抑制也可能有助于病毒的持续存在。这是纳罗病毒如何在人类细胞中建立持续性感染的潜在机制的首次提出。
