登革熱是一種藉由病媒蚊傳播登革病毒所造成的病毒性傳染病。登革病毒感染有可能是症狀較輕微的登革熱或具威脅性會致命的登革出血熱/登革休克症狀（DHF/DSS）；根據過去流行病學的研究顯示，受到不同病毒型交叉感染之登革病患容易發展成為後者。有人提出抗體依靠性增強作用假說（ADE）來解釋登革病毒引發登革出血熱/登革休克症狀之致病機轉；此理論基礎是認為初次感染登革病毒所產生的抗體無法在不同血清型的二次感染時中和病毒，抗體和病毒所形成的複合物反而會透過抗體的Fc部份和Fc受器結合，進而使病毒更容易感染表現Fc受器的細胞，如：單核球及巨嗜細胞等等，產生更大量病毒，最終發展成登革出血熱/登革休克症狀。然而，登革病毒感染之抗體依靠性增強作用仍有許多問題有待釐清！為了進一步探討抗體依靠性增強作用的發生，我們建立一試管內的感染模式，以研究抗體在抗體依靠性增強作用中所扮演的角色及其機制。由於在登革病人體內可以測到自體抗體的存在，且研究也顯示登革病毒可以在B細胞內進行複製，顯示了B細胞在登革病毒的感染過程及致病機轉中扮演了重要的角色；因此，我們首先選用人類B細胞株BJAB，建立登革病毒感染模式，並運用抗登革二型病毒抗原的單株抗體，配合流式細胞儀，建立一穩定且可快速偵測並定量病毒感染情形的系統。結果顯示，被登革二型病毒感染的BJAB細胞株內可測得病毒抗原包括非結構性蛋白1（NS1）、膜蛋白（E）及核心蛋白的表現；且用病毒溶斑測試（plaque assay）也可測得病毒顆粒的產生。登革二型病毒不僅可以在BJAB細胞株內複製，亦可活化之，使B細胞表面的CD70及CD86的表現量上升。實驗也發現，當次中和濃度（1:6000）的登革三型病毒感染病人血清存在下，登革二型病毒感染B細胞的能力會增強。我們也進一步分析登革病毒感染分泌抗登革病毒抗原融合瘤細胞的情形，意外地發現只有可分泌抗登革病毒前趨膜蛋白抗體（anti-preM Ab）的融合瘤細胞才可被登革病毒感染，這暗示了anti-preM Ab的存在可能增強登革病毒的感染能力。我們也進一步證實登革病毒感染表現Fc受器細胞株的能力的確會因anti-preM Ab的存在而增強；同樣的結果也可在部份不表現Fc受器的細胞株，如：幼倉鼠腎臟細胞（BHK）及人類肺部上皮細胞株（A549）等等被觀察到；然而，相同條件抗膜蛋白抗體（anti-E Ab）的存在下則不具增強病毒感染的能力。以上實驗結果證明抗前趨膜蛋白抗體的確參與了登革病毒的抗體依靠性增強作用，但其確切的作用機轉則需更進一步的研究。

　　Dengue virus (DEN) can cause either self-limited mild disease of dengue fever (DF), or severe dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). It is well known that children with secondary infection of a different serotype of dengue virus will cause more severe DHF/DSS that might be fatal. Antibody-dependent enhancement of infection (ADE) is widely accepted to be central to the development of these clinical entites. When the virus is bonded by sub-neutralizing or non-neutralizing antibodies from previous infection, the complex can be captured by Fc gamma receptor-bearing cells via the Fc portion of the immunoglobulins, and then enhances the viral entrance and replication. However, the mechanism responsible for this ADE phenomenon has not been clearly defined. In order to characterize it, we have set up an in vitro infectious model to study the role of enhancing antibodies on DEN infection. Because autoantibodies were found in DHF/DSS patients and B cell could support the DEN replication, we first chose a human B lymphoma, BJAB, as a model. The DEN serotype 2 (DEN2)-infected BJAB expressed dengue viral non-structural protein 1 (NS1), envelope protein（E） and core protein post infection that could be detected by flow cytometer. Infectious viral particles were detected by plaque assay in the culture supernatant. DEN2 not only replicated in BJAB cells but also activated them to up-regulate activation markers, including CD70 and CD86. A sub-neutralizing titer (1:6000) of heterologous DEN3-immune serum was able to enhance DEN2 infection in BJAB cells. Furthermore, a panel of hybridomas secreting antibodies recognizing different DEN2 antigens was infected by DEN2. Surprisingly, only those hybridomas secreting anti-DEN precursor membrane protein (anti-preM) antibodies could be infected. This implicates that anti-preM antibody may mediate the ADE. Indeed, the infection of DEN2 on Fc receptor-bearing cells, such as DC2.4 cell line and other non-permissible hybridoma, was enhanced at least 10 fold in the presence of anti-preM antibody. Anti-preM antibodies mediated enhancement could also be demonstrated on non-Fc receptor-bearing cells, such as BHK and A549. This enhancement was not found for anti-E antibodies. These studies can help us understand the characteristics of enhancing antibody, although its mechanism and biological significance need further investigation.

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