腸病毒71型的感染常在嬰幼兒引發重症，症狀包括無菌性腦膜炎、腦幹腦炎及急性無力肢體麻痺症，並伴隨肺水腫及心肺衰竭等併發症。即使病童從重症中存活下來，身上也常留有永久的神經性後遺症；然而目前對其致病機轉的了解仍然十分有限，也尚無可使用的疫苗或是專一性的抗病毒藥物。臨床研究發現，腸病毒71型感染的重症患者的血清及腦脊髓液中，比起輕症患者有顯著較多的γ干擾素；此外，γ-干擾素的量也隨患者病情而有變化，暗示γ-干擾素極可能在腸病毒71型感染扮演重要的角色。目前還沒有研究針對γ-干擾素在腸病毒71型感染中扮演的角色進行探討，所以我們在此利用小鼠模式來進行研究。研究結果發現，γ-干擾素在感染野生型小鼠的腦部明顯增加，與重症患者類似。因此，我們進一步使用γ-干擾素受體缺乏小鼠進行研究。感染之後，γ-干擾素受體缺乏小鼠的死亡率與疾病嚴重程度皆顯著比野生型小鼠高，γ-干擾素受體缺乏小鼠組織中也有明顯較高的病毒量。更進一步的研究結果顯示，γ-干擾素受體缺乏小鼠脾臟中的CD4、CD8 T淋巴球及巨噬細胞數量皆少於野生型小鼠。細胞實驗的結果也發現，γ-干擾素具有抑制病毒在神經細胞株的複製的功能，能顯著降低細胞的病毒量。另外，有鑑於本實驗室先前的初步結果顯示，腸病毒71型專一性抗體能有效預防腸病毒感染，我們在此更進一步分析了腸病毒71型專一性抗體的治療效果，結果顯示腸病毒71型專一性抗體能有效治療被感染的淋巴球(B、CD4 T或CD8 T淋巴球)缺乏小鼠，顯著降低其死亡率，除此之外，與目前臨床上使用來治療重症患者的靜脈注射人類免疫球蛋白相比，腸病毒71型專一性抗體具有較高的病毒中和效價，同時也能更有效的降低感染小鼠的死亡率。綜合以上結果，我們發現γ-干擾素在腸病毒71型感染後產生，並透過增加CD4、CD8 T淋巴球及巨噬細胞的數量或直接減少病毒在神經細胞中的複製，來減少組織中的病毒量，達到保護小鼠的效果。同時也建議使用腸病毒71型專一性抗體，於臨床上腸病毒71型重症的治療。

Enterovirus 71 (EV71) infection induces fatal aseptic meningitis, encephalitis, and acute flaccid paralysis, with cardiopulmonary complications, particularly in infants and young children. Unfortunately, the pathogenesis of EV71 infection remains elusive, and vaccines and anti-viral drugs are not available. Clinical reports have shown a significant elevation of interferon gamma (IFN-γ) in the serum and cerebrospinal fluid of EV71-infected patients with fatal symptoms. The level of IFN-γ was reduced in patients after intravenous immunoglobulin treatment. The role of IFN-γ in EV71 infection is still unclear. We therefore used a mouse model to address this issue. Results showed that the level of IFN-γ was elevated in the brains of infected wild-type mice, which is in agreement with the findings of infected patients. To investigate the role of IFN-γ in EV71 infection, we infected mice deficient in IFN-γ receptor 1 (IFN-γR1-/-). We found that after infection, both the mortality and disease severity of IFN-γR1-/- mice were significantly higher than those of wild-type mice. High viral loads were also found in the tissues of IFN-γR1-/- mice. Further study showed that, the numbers of CD4 and CD8 T lymphocytes and macrophages in the spleens of IFN-γR1-/- mice were reduced. Moreover, IFN-γ treatment significantly reduced EV71 replication in a mouse neuronal cell line. Besides investigating the role of IFN-γ in EV71 infection, we also tested the therapeutic effect of EV71-specific antibody because EV71-specific antibody given before infection is shown to prevent EV71-infected mice from death by reducing tissue viral loads. Here we found that EV71-specific antibody treatment given after infection significantly reduced the mortality and disease severity of lymphocyte-deficient mice, which are highly susceptible to EV71 infection, by reducing tissue viral loads. In addition, both the neutralizing titer and the therapeutic efficacy of EV71-specific antibody were higher than those of intravenous immunoglobulin, which is now used in the clinic to treat EV71-infected patients. Collectively, our results show that IFN-γ induced after infection functions to reduce the viral loads in tissues by increasing the numbers of CD4 and CD8 T lymphocytes and macrophages and by reducing viral replication in neuronal cells. Our results also show the potential of using EV71-specific antibody to treat EV71-infected patients.

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