摘要
摘要 豬第二型環狀病毒（Porcine circovirus type 2, PCV2）是一小型、無封套、環狀、單股DNA病毒。 PCV2已被證實是豬環狀病毒相關疾病（PCVD或PCVAD）的主要致病原。PCVAD的表現可能是臨床不顯性感染或是包含有一個或多個病徵綜合的臨床表現。組織病理學方面，PCVAD的特徵是患豬體內淋巴器官呈現T- 和B-淋巴細胞流失且伴隨有巨噬細胞浸潤及細胞激素反應的改變。研究顯示PCV2的感染可以成功逃避宿主免疫系統的攻擊，並可在豬隻體內存活很長一段時間而不產生臨床症狀，進而影響宿主的免疫力。 為了瞭解PCV2在PCVAD的形成中所扮演的角色，首先，針對血液單核球及單核球衍生的巨噬細胞以活體外的方式進行PCV2接種後，評估這些細胞的PCV2抗原陽性率、細胞融合率、細胞遷移能力及趨化因子如單核細胞趨化蛋白-1（MCP-1）和巨噬細胞炎性蛋白-1（MIP-1）等（第二章）的mRNA表現以釐清肉芽腫性炎症反應的產生；第二，針對肺泡巨噬細胞及血液單核球，探討感染細胞的吞噬能力、殺菌能力、細胞激素（interleukin, IL），包括 IL-8、組織壞死因子(TNF)-α，干擾素(IFN)-α及FasL的表現（第三章）及先天免疫反應調節基因的表現 （第四章及第五章），以瞭解PCV2如何藉由影響細胞的功能來促進疾病的發展。 研究結果顯示，單獨PCV2即可誘導豬隻單核吞噬細胞增殖、融合及趨化因子的表現。因此，PCV2在誘導PCVAD患豬體內肉芽腫炎症反應的產生上扮演一個顯著的角色（第二章）。在PCV2及豬生殖與呼吸綜合症病毒(porcine reproductive and respiratory syndrome virus, PRRSV) 共同感染的模式中，若豬肺泡巨噬細胞先感染PCV2再感染PRRSV或同時感染PCV2及PRRSV的條件下，會造成細胞PRRSV病毒抗原陽性率、細胞毒殺能力及TNF-α的表現量下降 （第三章）。 研究結果並顯示，來自PCV2臨床不顯性感染豬隻體內的血液單核球，其toll-like receptor (TLR)-9、interferon regulatory factor (IRF)-3、IRF-6、IRF-7、IL-6、IL-12p35、IL-12p40、及IFN-α的mRNA表現量，較健康未帶原豬隻體內血液單核球的表現量，有顯著的較低情形（第四章和第五章）。而在有PCV2重複感染 (第五章)及細菌內毒素LPS的刺激下(第四章)，TLRs、IRFs、IL-12及IFN-α的mRNA表現亮，則呈現一個更廣泛且更顯著的降低情形。相反地，NF-κB則不受PCV2重複感染及LPS刺激的影響，其mRNA表現量均呈現穩定向上調控的情形（第四章）。 在本研究中所發現的證據顯示，單獨PCV2即具誘導肉芽腫炎症反應形成的潛能（第二章），臨床上看似健康的不顯性PCV2感染豬隻實際上是處於一種免疫調控異常的狀態（第四章及第五章），而PCV2感染會導致巨噬細胞功能的改變（第三章），此等證據均再一次的證明PCV2感染豬隻的免疫狀態將使其較容易發生二次性細菌及/或病毒的感染，進而衍生成PCVAD患豬。
並列摘要
Abstract Porcine circovirus type 2 (PCV2) is a small, non-enveloped virus possessing a covalently closed, circular and single-stranded DNA genome. PCV2 has been demonstrated as the major etiologic pathogen of porcine circovirus disease (PCVD) or porcine circovirus-associated disease (PCVAD). PCVD or PCVAD can be subclinical or include 1 or more clinical manifestations of the syndrome. Histopathologically, PCVAD-affected pigs display T- and B-lymphocyte depletion, monocyte (Mo)/macrophage-lineage cell infiltration in lymphoid organs, and altered patterns of cytokine responses. PCV2 infection can remain asymptomatic in pigs for a long period of time by eliciting immune evasion strategies in target cells, which may subsequently lead to the impairment of the host immunity. To elucidate the possible role of PCV2 in the development of PCVAD, first, the PCV2 antigen-containing rate, cell fusion rate, cell migration, chemokine mRNA expression, such as monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1 (MIP-1), of target cells (Chapter II) were determined to evaluate the formation of granulomatous inflammation by using blood Mos and Mos-derived macrophages (MDMs); second, the phagocytotic and microbial killing capabilities, cytokine profiles (IL-8, TNF-α, and IFN-α) , FasL transcripts (Chapter III), and innate immune response-modulating genes (Chapter IV and V) were investigated in vitro to elucidate how PCV2 alter and dis-regulate the functions of the target cells to facilitate the disease development by using alveolar macrophage (AMs) and blood Mos, respectively. It was found that PCV2 alone may induce cell proliferation, fusion, and chemokine expression in swine monocytic cells. Thus, PCV2 itself may play a significant role in the induction of granulomatous inflammation in PCVAD-affected pigs (Chapter II). Swine AMs infected with PCV2 first then PRRSV later or infected with PCV2 and PRRSV simultaneously displayed marked reduction in PRRSV antigen-containing rate, cytopathic effect, and TNF-α expression level (Chapter III). Under the condition of no further treatment, Mos from pigs with subclinical PCV2 infection displayed significantly lower mRNA expression levels in TLR-9, IRF-3, IRF-6, IRF-7, IL-6, IL-12p35, IL-12p40, and interferon (IFN)-α than those from PCV2-free pigs (Chapter IVand V). A broader and/or more obvious spectrum of significant reduction in TLRs, IRFs, IL-12, and IFN-α were observed following PCV2 superinfection (Chapter V) and LPS stimulation (Chapter IV) in vitro. On the contrary, the mRNA expression level of NF-κB was consistently up-regulated with or without PCV2 superinfection (Chapter V) and LPS stimulation (Chapter IV). The evidences discovered in the present study suggest that PCV2 alone could induce formation of the granulomatous inflammation (Chapter II), the subclinically PCV2-infected pigs are actually in an immune dis-regulated status (Chapter IV and V), and many of the functions of PCV2-infected macrophages are altered (Chapter III). All of the above mentioned evidences further support the fact that PCV2-infection predisposes the affected pigs to the secondary bacterial and viral infection and leads to the development of PCVAD.
參考文獻
延伸閱讀
- Hung, L. C. (2017). 豬第二型環狀病毒抗原決定位之篩選 [doctoral dissertation, National Taiwan University]. Airiti Library. https://doi.org/10.6342/NTU201704287
- 蘇少儀、鍾明華、楊平政、賴秀穗、潘居祥、黃天祥、劉振軒、吳應寧（2010）。商業豬群中豬生殖與呼吸綜合症病毒第二型與豬二型環狀病毒感染盛行率之研究。臺灣獸醫學雜誌，36(3)，238-247。https://doi.org/10.7009/TVJ.201009.0238
- 劉俊廷（2008）。不同細菌脂多醣體對豬第二型環狀病毒於豬肺泡巨噬細胞內複製作用之探討〔碩士論文，國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342/NTU.2008.10379
- 邱淑君（2014）。豬鐵士古病毒致病機轉之再探討〔博士論文，國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342/NTU.2014.00123
- 林欣怡（2016）。Extraction and Purification of Porcine Circovirus Type 2 Capsid Protein as the Virus-like Particle Vaccine〔碩士論文，國立清華大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0016-0411201614421415