EB病毒對於星狀細胞株之感染及影響

Abstract

EB病毒 (Epstein-Barr virus, EBV) 的感染可能造成感染性單核球增多症 (infection mononucleosis, IM) ，並與許多惡性腫瘤高度相關。少部分因EB病毒感染的IM患者可能發生中樞神經系統 (central nervous system, CNS) 發炎併發症，如腦炎及脊髓炎。在許多CNS發炎病症患者的腦脊髓液中可檢測到EB病毒的遺傳物質或抗EB病毒之抗體。星狀細胞 (astrocyte) 為CNS中占最大比例的細胞，主要功能為維持CNS的生理機能，如養分的運輸及維持血腦屏障等。除此之外，星狀細胞也是CNS重要的免疫細胞。在前人研究中發現EB病毒能夠感染人類星狀細胞，因此本研究欲探討EB病毒感染星狀細胞株之後對於星狀細胞株生物功能所造成的影響。本研究以抗人類免疫球蛋白G刺激帶有GFP螢光標定EB病毒之Akata-EBV-EGFP細胞使EB病毒進入溶裂期複製病毒，再與人類星狀細胞株U-87 MG、U-251 MG及U-1240 MG共同培養以感染星狀細胞株，接著以G418篩選出EB病毒陽性之星狀細胞株。EB病毒於星狀細胞株中表現LMP1及EBNA1病毒蛋白，以及EBNA1、LMP1、LMP2A、EBER1、EBER2、Zta等病毒基因mRNA，推測EB病毒在星狀細胞株中可分類為潛伏期第二型。EB病毒陽性之星狀細胞株外型較控制組細胞株為細長，且活化標記蛋白GFAP表現量上升，顯示星狀細胞株可能因EB病毒感染而被活化。為進一步了解EB病毒在星狀細胞株是否能夠進入溶裂期並活化星狀細胞株，結果顯示同時表現Zta及Rta能夠促進病毒早期蛋白的表現，並可觀察到星狀細胞中活化標記蛋白表現量上升。在CNS中IL-1β為重要的細胞素，且已知能夠促進星狀細胞活化並表現多種細胞素，為了解EB病毒潛伏的星狀細胞是否在有其他刺激時會造成不同反應，故以IL-1β刺激星狀細胞株。結果顯示，EB病毒陽性之星狀細胞株受到IL-1β刺激後，其IL-6及IL-8 mRNA表現量明顯上升，且遠高於IL-1β刺激後的控制組細胞；但EB病毒陽性細胞在受到刺激後，TNF-α上升量略低於控制組細胞。上述實驗結果推測EB病毒感染星狀細胞可能使星狀細胞活化，並且在星狀細胞受到刺激時加劇其對於刺激的反應。

Epstein-Barr virus (EBV) is etiologic agent of infection mononucleosis (IM) , and has been linked to many cancers. Central nervous system (CNS) complications, including encephalitis and meningitis, occur in some of patients with IM. EBV genomes and anti-EBV antibodies have been found in the cerebrospinal fluid from many patients with these diseases. Astrocytes are the most abundant cells in CNS, and play major roles in CNS biological function, such as providing nutrients for neuron, maintaining blood brain barrier, and immune response in the CNS. It was found that EBV can infect human astrocyte cell lines. Therefore, we want to investigace the biological effects of EBV in astrocyte cell lines. To this end, different astrocyte cell lines, U-87 MG, U-251 MG and U-1240 MG were co-cultured with anti-human IgG stimulated Akata cells containing GFP tagged EBV for EBV infection. After selection with G418, EBV positive U-87 MG and U-251 MG cells were established. EBV-infected astrocyte cell lines showed elongated morphology, and upregulated GFAP expression. EBV positive astrocytes expressed viral gene products, including LMP1, EBNA1, and viral RNAs for LMP1, LMP2A, EBNA1, EBER1, EBER2, Zta. The status of EBV in astrocyte cell lines belongs to type Ⅱ latency. To reveal whether EBV in astrocyte could be reactivated into lytic cycle and resulted in astrocyte cell lines activation, Zta and Rta expression plasmid were transfected to EBV positive astrocyte cell lines and control cell lines. We found that EBV in U-251 MG was induced into lytic cycle, and GFAP expression in this astrocyte cell line was upregulated. To explore whether EBV infection affects astrocyte response to stimulator treatment, astrocyte cell lines were treated with IL-1β which activates astrocytes and induces the expression of many cytokines. In comparison with control cells, the expression of IL-6 and IL-8 mRNA was obviously increased in EBV positive cells after IL-1β treatment. However, TNF-α expression increased slightly in EBV positive astrocyte cell lines after IL-1β treatment, compared to control cells. Taken together, we suggest that EBV infection activates astrocyte cell lines, and affect astrocyte response to other stimulation.