醣類代謝差異影響桿狀病毒感染專一性之研究

Abstract

桿狀病毒為為雙股環狀DNA病毒，在自然界中可以感染多種節肢動物，而最主要的寄主則通常為鱗翅目幼蟲。加州苜蓿夜蛾核多角體病毒 (AcMNPV) 為目前研究最廣泛的桿狀病毒，並且可以感染多達39種的昆蟲，而家蠶核核多角體病毒 (BmNPV) 是一種對於家蠶有高度宿主專一性的桿狀病毒。這兩種桿狀病毒在序列及基因結構性具有高度相似性，但在寄主的範圍卻沒有任何重疊，BmNPV 只會感染家蠶 (Bombyx mori)，而AcMNPV的允許寄主 (permissive host) -斜紋夜蛾 (Spodoptera litura) 則無法被BmNPV感染，這種寄主專一性的現象非常特別，前人研究著重於研究病毒基因對於寄主專一性所造成的影響，但寄主專一性可以被許多不同因素影響，本研究則從寄主生理代謝的變化方向去切入。在本研究所得到的結果指出，在病毒感染了非允許寄主 (non-permossive host) 後，寄主體內血淋巴中的海藻糖含量減少，而接著在海藻糖酶及糖原磷解酶的表現量上升代表了酵素的作用使得寄主體內儲存糖被分解成細胞可利用之葡萄糖，而也接連影響了脂肪體中葡萄糖的含量及糖解作用的改變，因病毒並不能在非允許寄主體內複製，我們推測這些能量上的改變可能是為了提供給昆蟲的免疫系統，實驗結果也證明了在感染病毒後，非允許寄主體內細胞性免疫的吞噬作用增加，參與體液性免疫的基因表現量也上升，非允許寄主體內體液性免疫最下游之抗菌肽的表現量也因為病毒的感染而增加，免疫系統的啟動可能是造成病毒無法在非允許寄主體內複製的原因之一，進而利用 2DG 抑制寄主的醣類代謝使寄主無法產生能量後，病毒感染非寄主的能力上升，也證明病毒的寄主專一性與寄主體內醣類代謝有一定的關聯。本研究利用探討病毒感染後寄主的生理代謝變化，證明了寄主自身生理代謝可能是影響病毒感染專一性的原因之一。

Baculoviruses are double-stranded circular DNA viruses with genomes of approximately 80-180 kb. They can infect many arthropod species, with lepidoptera larvae being the most common host. Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV), which can infect 39 species of lepidoptera, is the most studied baculovirus to date. Bombyx mori nucleopolyhedrovirus (BmNPV) is a major silkworm pathogen which has developed high host specificity to Bombyx mori. These two viruses are very similar in genetic structure and sequence, but have no overlapping host range. BmNPV can only infect Bombyx mori, but Bombyx mori cannot be infected by AcMNPV. Similarly, Spodoptera litura, the permissive host of AcMNPV, cannot infected by BmNPV. Many previous studies have discussed the conditions which affect the host specificity of these two viruses. Our study found that when AcMNPV and BmNPV infect their non-permissive hosts, the blood sugar composition of the host will be changes, thus causing changes in carbohydrate metabolism. We believe that these changes in energy flow may induce the immune response of non-permissive hosts. Our research has confirmed that after infection with non-permissive viruses, both cellular and humoral immunity are enhanced. Humoral response involves the production of various antimicrobial peptides (AMPs). Our results show that gloverin, a kind of antimicrobial peptides, may be an important factor that influences baculovirus infection. The activation of the immune system may be one of the reasons why the virus cannot replicate in non-permissive hosts.