登革病毒屬於黃熱病毒科是一種盛行於熱帶及亞熱帶地區的媒蚊傳播病毒。登革病毒感染後出現的症狀包含紅疹、發燒、頭痛、肌肉和關節痛等，大多會自行痊癒，但仍有一小部分病患會發展為危及生命的登革重症，例如登革出血熱或登革休克症候群。先前文獻指出登革病毒可以感染骨髓中的造血幹細胞及其前驅細胞，導致許多血液相關疾病像是血小板低下症、白血病以及白血球低下症等。表現CD61的髓細胞也曾被報導指出是登革病毒感染骨髓的主要細胞之一。此外，我們實驗室也發現到膜蛋白CD44同時也是玻尿酸(HA)的受體，可能是登革病毒感染皮膚幹細胞的潛在受體。因此我們想去研究表現在髓細胞上的膜蛋白CD44是否也會作為一個潛在的受體去幫助登革病毒感染髓細胞。所以我們先檢測髓細胞中膜蛋白CD44的表現量，並利用玻尿酸去阻礙膜蛋白CD44的表現，以檢測其對於登革病毒感染細胞的影響。我們挑選了髓細胞體系的巨核細胞株K-562及MEG-01細胞作為本研究中病毒感染實驗的細胞。首先，我們先確認了這兩株細胞皆能受登革病毒感染，接著利用流式細胞儀分析膜蛋白CD44在兩株細胞中的表現，結果顯示，膜蛋白CD44在MEG-01細胞中表現高，但在K-562細胞中表現較低。為了進一步去研究膜蛋白CD44在登革病毒感染的過程中是否扮演重要的角色，我們利用玻尿酸去阻礙兩種細胞中膜蛋白CD44的表現，再以登革病毒感染細胞，並檢測病毒產生的情況。結果顯示，在兩種細胞株中，不論有無玻尿酸阻礙膜蛋白CD44的表現，對於登革病毒感染皆無差異。我們也將幹細胞分選出來，並以玻尿酸阻礙膜蛋白CD44的表現，結果也一樣。為了更直接去抑制膜蛋白CD44的表現，我們利用特製的小分子干擾核糖核酸(siRNA)去降低CD44的表現，接著以登革病毒去感染細胞。意外地，結果顯示，利用小分子干擾核糖核酸抑制MEG-01細胞中CD44的表現的組別，細胞中登革病毒的病毒核糖核酸表現量下降。總結以上，CD44可能會作為登革病毒進入MEG-01細胞之受體。

Dengue virus (DENV) is one of the members of the Flaviviridae family, and is the most common arbovirus in tropical and subtropical areas. Clinical symptoms in infected people include rash, fever, headache, muscle and joint pains. While majority of affected subjects are self-limited illness, but a small percentage of affected individuals may progress into life-threatening conditions, such as dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). Previous results show that DENV can infect hematopoietic stem and progenitor cells (HSPC) in bone marrow (BM), resulting hematological disorders, such as thrombocytopenia, leukemia, and leucopenia in patients. CD61+ cells have been demonstrated to be one of the predominant cells for DENV infection in BM. Recently, CD44, a cell-surface glycoprotein and receptor for hyaluronic acid (HA), expressing in skin stem cells has been suggested to be a potential receptor for DENV infection. Therefore, we investigated whether myeloid cells expressing CD44 were correlated to the permissiveness to DENV infection. K-562 and MEG-01 cells were selected as the representative of myeloid cells for the study. The expression levels of CD44 in these two cells were checked by FACS, and the function of CD44 in these cells for permissiveness of DENV infection was performed by blocking CD44 with its natural ligand, HA. We confirmed that both K-562 and MEG-01 cells were permissive to DENV infection. FACS analysis revealed that CD44 expressed high levels in MEG-01 cells, but very low in K-562 cells. To investigate the role of CD44 in DENV infection, we used HA to block the CD44 in K-562 and MEG-01 cells followed by DENV infection in these cells, respectively. Kinetically, the viral titers in supernatants of DENV-infected K-562 or MEG-01 cells, were no differences between HA-blocked group and the control group. Furthermore, sorting out the stem cells from K-562 or MEG-01 cells, blocked with HA followed by DENV infection, respectively. Results also indicated that there were no differences in viral titers between HA-treated or control groups, suggesting that CD44 blocking by its ligand, HA, may not play a role for DENV infection in stem cells of these cells. Since there are multiple forms of CD44, in order to more specific to identify the functions of CD44 in DENV infection, we used siRNA sequences to knockdown CD44 in K-562 or MEG-01 cells prior to DENV infection. The results showed that viral RNA was decreased in CD44 knock down group in MEG-01 cells. The results suggest that a form of CD44 that is unrelated to its natural ligand, HA, could be the potential receptor for DENV infection in MEG-01 cells.

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