第一型干擾素調控漿狀樹突細胞亞群生長及功能之研究

Abstract

樹突細胞(Dendritic cells, DC)是一種專門的抗原呈現細胞 (antigen presentation cell)，並且為連接先天性免疫系統 (innate immune system) 及適應性免疫系統 (adaptive immune system) 的重要橋梁。樹突細胞主要可分為傳統樹突細胞 (conventional DC, cDC) 以及漿狀樹突細胞 (plasmacytoid DC, pDC) 兩種亞型，它們可由骨髓前驅細胞如巨噬樹突前驅細胞 (macrophage DC progenitor) 或共同樹突細胞前驅細胞 (common DC progenitor, CDP) 以及淋巴前驅細胞，如共同淋巴前驅細胞 (common lymphoid progenitor, CLP)分化而來。pDC以其受到病毒感染時，能夠分泌大量的第一型干擾素 (type I IFN, IFN-I) 而著名，然而，究竟IFN-I是如何調控漿狀樹突細胞亞群的生長及功能，目前尚未完全釐清。離體 (ex vivo) 功能試驗中， 與野生型 pDC 相較之下，受到類鐸受體9 (Toll-like receptor 9, TLR9) 配體的刺激後，Ifnar1-/- pDC表現較低的CD86與產生較少量的促炎細胞激素 (proinflammatory cytokines) 及IFN-I。此外，信號轉導子和轉錄激活子 (signal transducer and activator of transcription，STAT) 1 基因剃除(Stat1-/-) pDC以及STAT2基因變異(Stat2m/m) pDC 也有功能缺失的現象。另一方面，在Ifnar1-/-和 Stat2m/m 的骨髓及脾臟中，兩種pDC亞群－CD4+CD8+ 與 CD4+CD8- pDCs 則有顯著地減少。而Ifnar1-/- pDC 在受到刺激後，所有亞群所產生的IL-6 與IFN-I也是較少的。CD4-CD8- pDC亞群在活化後相較於其他亞型而言有較高量MHC-II以及CD86的表現，同時分泌較大量的IL-6。此外，Ifnar1剔除的骨隨細胞體外培養下有較少pDC生成，並且當我們使用高濃度FL在體外 (in vitro) 培養，也無法挽救Ifnar1-/- 鼠的pDC生長及功能缺失。綜合以上，研究結果顯示第一型干擾素藉由STAT1與STAT2的路徑在pDC功能扮演正向調控的角色，並且，受到CpG刺激時，CD4-CD8- pDCs為四個pDC亞群中活化程度最強烈而可能是最成熟的一個亞群。

Dendritic cells are professional antigen presenting cells which connect innate and adaptive immune system throughout lymphoid organs. Conventional DC and plasmacytoid DC are the two major DC populations, which can be generated from both myeloid progenitors, such as macrophage DC progenitor and common DC progenitor (CDP), and lymphoid progenitors, such as common lymphoid progenitor (CLP). pDCs are known for their ability to produce robust amount of IFN-I during virus infection. However, it is still not completely understood how IFN-I regulates pDC subsets development and functions. Ex vivo functional assay showed that Ifnar1-/- pDC expressed lower level of CD86, and produced less proinflammatory cytokines and IFN-I than did WT pDC in response to a TLR9 ligand. In addition, Stat1-/- and Stat2m/m pDC also displayed impaired functions, which is consistent with Ifnar1-/- pDC. Interestingly, the amount of CD4+CD8+ and CD4+CD8- pDCs, two subsets of pDCs, was significantly diminished in Ifnar1-/- BM and spleen. Moreover, production of IL-6 and IFN-I were reduced in Ifnar1-/- pDC subsets upon CpG ODN stimulation. Among 4 different pDC subsets, CD4-CD8- pDC express the highest levels of MHC-II and CD86, and produce the greatest amount of IL-6 in response to CpG stimulation, compared to the other three subsets. In vitro BM culture showed that Ifnar1-/- BM developed fewer pDC and the impaired pDC development and functions in the absence of IFNAR1 could not be rescued supplemented with high dose FL. Taken together, IFN-I play a positive role in regulating pDC functions via STAT1 and STAT2 pathway, and CD4-CD8- pDCs are more activated and may represent the most mature population of pDCs after CpG stimulation.