登革病毒主要分布在熱帶與亞熱帶地區，現已在超過100多個國家流行。根據世界衛生組織的資料統計，估計全球每年約將近3.9億人口感染登革病毒。受到登革病毒感染的人們可分為有症狀及無症狀者，有症狀的病人會出現典型的發燒、頭痛、肌肉痛等症狀，並且有少數的病人會發展成登革重症，包含登革出血熱、休克等等；而根據統計，有超過75%的人被感染後是無症狀者(登革健康感染者)，因此需透過實驗室診斷，才會知道自己曾經感染過登革病毒。並且登革健康感染者會成為病毒的攜帶者，特別在病毒血症期間更容易傳播病毒。由先前實驗室研究得知，登革健康感染者的單核球對於登革病毒的清除能力較健康人來得差，並且發現其單核球再次受到登革病毒感染後，傾向於釋放能招募適應性免疫細胞的訊號。因此，我們的假說是登革健康感染者再次受登革病毒感染後之單核球以及T細胞會有功能上的改變。我們收集登革疫區之健康感染者以及非登革疫區健康人的周邊血，從中分離出單核球後，進行登革病毒感染，接著了解其細胞激素與趨化因子分泌的結果；另一部分與同樣從周邊血分離出來的T細胞共培養，並利用細胞的標定蛋白與流式細胞儀來分析。CD4及CD8為T細胞的標的，CD25能標定活化型T細胞，CFSE及Ki67用於分析T細胞的增生與分裂，γ型干擾素用於分析T細胞的抗病毒功能。在單核球分泌細胞激素與趨化因子的實驗中，我們發現從登革健康感染者分離出來的單核球，其分泌腫瘤壞死因子-α以及介白素-8有輕微增加，而介白素-6以及介白素-10則輕微的減少，巨噬細胞移行抑制因子則維持相同的程度，但並無統計上的差異。代表登革健康感染者的單核球本身利用細胞激素來抗病毒的功能並沒有受到影響。此外，我們發現來自登革健康感染者的T細胞，與登革病毒再次感染後之單核球共培養後，其細胞增生的能力隨著時間有顯著的下降。然而，不管是從健康人或是登革健康感染者分離出來的單核球，在受到登革病毒感染後，並無法被誘導成抗原呈現細胞，因此T細胞分泌γ型干擾素的能力無法被啟動。後續我們加入T細胞的激活因子活化T細胞，發現T細胞的增生會隨著時間持續上升，同時也能去證明上述T細胞增生的減少，可能是受到登革病毒感染之單核球的影響。此外，隨著T細胞被激活，能觀察到T細胞分泌γ型干擾素的表現明顯增加，並且我們發現登革健康感染者的T細胞對於γ型干擾素分泌的能力有延遲的現象。因此我們進一步想知道T細胞本身的功能是否有所改變。隨後我們利用登革病毒非結構蛋白3胜肽刺激T細胞，觀察T細胞的記憶性反應。實驗結果顯示，登革健康感染者的T細胞受到登革病毒非結構蛋白3胜肽刺激後，其γ型干擾素分泌的程度有輕微的減少。因此我們認為，登革健康感染者的單核球抗病毒的能力有受到改變，包含對病毒清除能力較差、以及影響的T細胞的增生能力，並且也無法誘導T細胞分泌γ型干擾素。同時，我們也認為登革健康感染者的T細胞其分泌γ型干擾素的能力也有一定程度上的變化。

Dengue is one of the most troublesome mosquito-borne infectious diseases in tropical and sub-tropical zones. Majority of people infected with dengue virus (DENV) are asymptomatic, and only a small population of succumb to severe dengue. Previous RNA array data suggested that monocytes were more anergy to DENV infection, and more toward to signaling pathways for adaptive immune cells upon re-stimulation with DENV in previously exposed subjects, suggesting that individuals exposed to DENV previously, despite monocytes were capable of inducing robust immune response, but had limited function in viral clearance. These results also hint an alternate mechanism in clearance of virus between naïve and previously DENV-exposed subjects. Monocytes were sorted out from peripheral blood mononuclear cells (PBMC) of naïve and previously DENV-exposed donors after signing consent, respectively, and challenged with DENV for cytokine analysis, and for co-culturing with the corresponding sorted T cells from PBMC and the T cells were subsequently subjected to FACS analyses by utilizing specific cell and functional markers including CD4, CD8 for T cell population, CD25 for T cell activation, IFN-γ for T cell function, and CFSE, Ki67 for T cell proliferation. Our results demonstrated that the levels of inflammatory cytokines, TNF-α and IL-8 were slightly higher, while IL-6 and IL-10 were slightly lower in previously DENV-exposed individuals. In addition, the levels of MIF were similar between naïve and previously DENV-exposed subjects. DENV-infected monocytes could have an effect on CD4 T cells function by the decrease of cell proliferation from previously DENV-exposed subjects. Also, we demonstrated that monocytes may not be an antigen-presenting cells during DENV infection, which hint monocytes did not alter T cells function directly. Moreover, the secretion of IFN-γ was delaying in the presence of CD3/CD28 activators, suggesting that the functions of T cells from previously DENV-exposed subjects may be irregular, and perhaps the viral clearance. Further, we utilized DENV NS3 peptides to stimulate T cells directly to investigate memory response of T cells. The results showed that IFN-γ secretion from memory T cells after NS3 peptides stimulation slightly decreased in previously DENV-exposed subjects. In conclusion, the functions of monocytes and T cells from previously DENV-exposed individuals were less response to DENV re-infection, moreover, monocytes from previously DENV-exposed subjects were less efficient to instigate with T cells compared to naïve subjects.

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