肝炎病毒感染是目前主要引起急性和慢性肝炎的主因，同時也是世界公共衛生上一個重要的議題。其中，由B型和C型肝炎病毒所引起的慢性肝炎往往會導致更嚴重的肝臟病變，例如：肝硬化和肝細胞癌等。過去的研究指出，在C型肝炎病毒感染的病人的血清中發現，帶有C型肝炎病毒RNA的顆粒出現在不同的血清密度範圍 (從1.03到1.25 克/毫升)，而其中感染力最高的部分是位於低密度的部分 (小於1.06克/毫升)。帶有C型肝炎病毒RNA的低密度顆粒被證實會與宿主血液中的β脂蛋白 (低密度脂蛋白和極低密度脂蛋白)有結合的現象，並富含三酸甘油酯、脂蛋白元B (apolipoprotein B)、C型肝炎病毒RNA、C型肝炎病毒核蛋白 (core protein)，因此有研究人員將其命名為病毒脂質顆粒 (lipo-viral particle)。 然而，目前對於C型肝炎病毒脂質顆粒的了解仍不是十分清楚。在本研究中，我們使用鹽類梯度離心的方式來分離血清的低密度部分，發現了在C型肝炎病毒感染的病人的血清低密度部分有著較高的C型肝炎病毒RNA含量 (佔總血清的48.3 ± 27.7 %)、β脂蛋白和免疫球蛋白G，但這種現象並未在B型肝炎病毒感染的病人的血清低密度部分發現。在使用表面活性劑處理之後，我們發現C型肝炎病毒RNA會被RNA分解脢 (RNase)給分解 (下降約4.4 log10/ml, p=0.003)，指出了C型肝炎病毒脂質顆粒中的脂質部分可能具有保護C型肝炎病毒RNA的功能。此外，在穿透式電子顯微鏡的觀察下我們發現，在C型肝炎病毒感染的病人的血清低密度部分，其低密度顆粒的大小分佈情形有右移的趨勢，而在B型肝炎病毒感染的病人和無B型及C型病毒感染的健康捐血者的血清低密度部分則沒有發現到這種現象。同時，我們使用了表面結合有與C型肝炎病毒RNA專一性互補的寡核酸的奈米金顆粒來偵測C型肝炎病毒RNA所存在的位置，發現了有許多奈米金顆粒的訊號出現在我們懷疑是C型肝炎病毒脂質顆粒之中。總合以上結果，我們推論大部分的C型肝炎病毒RNA是被包裹在β脂蛋白中，而病毒脂質顆粒中的脂質部分可能具有保護C型肝炎病毒RNA的功能。

Hepatitis B and C viruses (HBV) and (HCV), two major etiological agents of liver diseases, chronically infect millions of individuals in global population. Spherical HBV virion of 42 nm in diameter, known as Dane particle, has been well recognized, whereas rarely identified such HCV virion in plasma from infected patients. Circulating HCV particles exhibit a heterogeneous density. The low-density HCV fractions which may be due to association with β-lipoproteins have the highest infectivity among the other fractions with high densities. The purified low-density HCV RNA-containing particles were rich in triglycerides, containing at least apolipoprotein B, HCV-RNA, and HCV-core protein, which were named as lipo-viral particles (LVPs). However, the functional characteristics of LVPs remained unclear. In this study, salt gradient combined with ultracentrifugation was exploited to isolate the low-density fraction of plasma samples from blood bank donors who came under occult HBV or HCV infections. The results showed that the low-density fraction of HCV+ plasma contained a substantial amount of viral genome (48.3 ± 27.7% of total plasma HCV-RNA), but the corresponding fraction of HBV+ plasma had only a tiny amount (1.4 ± 0.8% of total plasma HBV-DNA). In a nuclease sensitivity assay, pretreatment of isolated HCV LVP with detergent triton X-100 could yield RNase-mediated degradation of HCV-RNA (decreased by 4.4 log10/ml, p=0.003). However, the HCV-RNA remained resistant to RNase digestion upon pretreatment with proteinase K. The results suggested that the lipid but not protein components of LVPs might be responsible to protect HCV-RNA. Furthermore, the size distribution of low-density particles was skew to the right in samples with HCV as compared to those with HBV or with neither HCV nor HBV. Additionally, nanogold conjugated HCV-specific oligonucleotide probes were used to detect HCV-RNA in the middle of LVP, suggesting that HCV genome might be incorporated into host lipoproteins. In conclusion, surrounding HCV-RNA by low-density lipoprotein particles might protect HCV genome in circulation. The results shed some light on HCV biology and hold potentials in the development of new anti-HCV strategy.

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