登革熱病毒於神經細胞內感染與複製能力之研究

Abstract

登革熱病毒（ Dengue virus, DV ） 及日本腦炎病毒（ Japanese Encephalitis Virus, JEV）皆屬於蚊蟲叮咬傳播的黃質病毒家族，具有相似的基因組態。感染日本腦炎病毒，於臨床上可能出現腦炎或腦膜炎等症狀。目前病理學的研究方面指出，日本腦炎病毒感染會傷害大腦或中樞神經系統，實際上致病的機制尚待進一步研究。登革熱病毒的患者於臨床上除了發熱外，可能出現出血與休克等症狀，依嚴重程度區分為登革熱（Dengue fever，DF），登革出血熱（Dengue hemorrhage fever，DHF）與登革休克熱（Dengue shock syndrome，DSS）等。這兩種病毒引起的臨床上的病徵，尤其是導致神經病變的機率差異很大。相對於日本腦炎而言，登革熱很少造成人類神經方面的感染。這兩種病毒的致病機制、體內感染途徑、造成神經毒性的關鍵都還不清楚，仍需進一步研究。本實驗使用免疫螢光染色的影像技術，配合影像分析軟體，觀察日本腦炎病毒與登革熱病毒在包括幼倉鼠腎臟纖維母細胞 BHK-21、白線斑蚊細胞 C6 / 36、小鼠初代神經細胞中，病毒感染與複製的情形。又因為登革熱病毒感染後主要的癥狀出現於人類，故本實驗亦針對人類神經瘤細胞IMR-32 測試日本腦炎病毒以及登革熱病毒的感染力。本研究中發現小鼠初代神經細胞以及人類神經瘤細胞不只能被日本腦炎病毒感染，也能被登革熱病毒感染。並且，在幼倉鼠腎臟纖維母細胞BHK-21 以及蚊子細胞 C6 / 36 中，這兩種病毒皆能複製且趨勢相似。根據實驗結果，登革熱病毒在臨床上導致腦炎的機率很低並不是因為登革熱病毒無法感染神經細胞，或無法在神經細胞內複製所導致。

Abstract Both Dengue viruses (DV) and Japanese encephalitis virus (JEV) are mosquito-borne flaviviruses. They share the same genomic organization and both are positive-sense, single-stranded RNAs. However, the symptoms of their infection are very different. JEV causes severe, even lethal encephalitis in humans. Pathological studies of JEV have shown that developing neurons are the major target of JEV. The DV complex consists of four serotypes (DV1-DV4). They may cause dengue fever (DF), dengue hemorrhagic fever (DHF), or dengue shock syndrome (DSS). Interestingly, most flaviviruses but DV cause neurotropism. Possibilities are that DV has difficulty to enter or propagate in neurons. Hence, I employed imaging technique to determine if DV2 and JEV can infect neurons by investigating the accumulation kinetics of viral replication in mouse primary neurons and mosquito cells. Since dengue symptoms are limited to human, I also analyzed the viral infectivity of DV2 and JEV in human neuroblastoma IMR-32. The results showed that both human and mouse neurons could be infected not only by JEV but also by DV2. And, the accumulation kinetics for DV and JEV were similar in the mouse primary neurons and mosquito cells. Hence, DV rarely causing neurotropism is not due to inability of infectivity and/or replication in neuron cells.