BACKGROUND & AIMS Natural killer (NK) cells are found at increased frequencies in patients with hepatitis C virus (HCV). NK cell activation has been shown to correlate with HCV clearance and to predict a favourable treatment response. The aim of our study was to dissect mechanisms leading to NK cell activation and proliferation in response to HCV. METHODS NK cell phenotype, proliferation, and function were assessed after the 6-day co-culture of human peripheral blood mononuclear cells with either HCV replicon-containing HuH6 hepatoblastoma cells or HCV-infected HuH7.5 cells. The results obtained were confirmed by immunohistochemistry of liver biopsies from patients with HCV and from HCV-negative controls. RESULTS In HCV-containing co-cultures, a higher frequency of NK cells upregulated the expression of the high-affinity IL-2 receptor chain CD25, proliferated more rapidly, and produced higher amounts of interferon γ compared with NK cells from control co-cultures. This NK cell activation was dependent on IL-2, cell-cell contact-mediated signals, and HCV replicon-exposed monocytes. The tumour necrosis factor-receptor superfamily member OX40 was induced on the activated CD25± NK cell subset and this induction was abrogated by the depletion of CD14+ monocytes. Moreover, OX40L was upregulated on CD14± monocyte-derived cells co-cultured with HCV-containing cells and also observed in liver biopsies from patients with HCV. Importantly, blocking of the OX40/OX40L interaction abolished both NK cell activation and proliferation. CONCLUSIONS Our results uncover a previously unappreciated cell-cell contact-mediated mechanism of NK cell activation and proliferation in response to HCV, mediated by monocyte-derived cells and the OX40/OX40L axis. These results reveal a novel mode of crosstalk between innate immune cells during viral infection. LAY SUMMARY Using a cell-culture model of hepatitis C virus (HCV) infection, our study revealed that natural killer (NK) cells become activated and proliferate when they are co-cultured with HCV-containing liver cells. The mechanism of this activation involves crosstalk with other innate immune cells and a cell-cell contact interaction mediated by the cell surface molecules OX40 and OX40L. Our study reveals a novel pathway leading to NK cell proliferation and activation against virus-infected cells that might be of relevance in antiviral immunity.

中文翻译：

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丙型肝炎病毒诱导的自然杀伤细胞增殖涉及单核细胞衍生细胞和 OX40/OX40L 轴

背景和目的 在丙型肝炎病毒 (HCV) 患者中发现自然杀伤 (NK) 细胞的频率增加。NK 细胞活化已被证明与 HCV 清除相关并预测有利的治疗反应。我们研究的目的是剖析导致 NK 细胞激活和增殖以响应 HCV 的机制。方法 在人外周血单核细胞与含有 HCV 复制子的 HuH6 肝母细胞瘤细胞或感染 HCV 的 HuH7.5 细胞共培养 6 天后，评估了 NK 细胞的表型、增殖和功能。获得的结果通过来自 HCV 患者和来自 HCV 阴性对照的肝活检的免疫组织化学证实。结果 在含 HCV 的共培养物中，与来自对照共培养物的 NK 细胞相比，更高频率的 NK 细胞上调高亲和力 IL-2 受体链 CD25 的表达，增殖更快，并产生更多的干扰素 γ。这种 NK 细胞活化依赖于 IL-2、细胞-细胞接触介导的信号和暴露于 HCV 复制子的单核细胞。肿瘤坏死因子受体超家族成员 OX40 在活化的 CD25±NK 细胞亚群上被诱导，这种诱导被 CD14+ 单核细胞的消耗所废除。此外，OX40L 在与含 HCV 细胞共培养的 CD14± 单核细胞衍生细胞上上调，也在 HCV 患者的肝活检中观察到。重要的是，OX40/OX40L 相互作用的阻断消除了 NK 细胞的激活和增殖。结论 我们的研究结果揭示了一种以前未被重视的细胞 - 细胞接触介导的 NK 细胞激活和增殖响应 HCV 的机制，由单核细胞衍生细胞和 OX40/OX40L 轴介导。这些结果揭示了病毒感染期间先天免疫细胞之间的一种新的串扰模式。概述使用丙型肝炎病毒 (HCV) 感染的细胞培养模型，我们的研究表明，当自然杀伤 (NK) 细胞与含 HCV 的肝细胞共培养时，它们会被激活并增殖。这种激活的机制涉及与其他先天免疫细胞的串扰以及由细胞表面分子 OX40 和 OX40L 介导的细胞间接触相互作用。