在發炎和感染下重新改變樹突細胞的發育

Reprogramming of dendritic cell development by inflammation and infection

蕭又綾(Yu-Ling Hsiao)

指導教授 ： 李建國

國立臺灣大學/醫學院/免疫學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802330

摘要

樹突細胞包含漿狀樹突細胞和傳統樹突細胞，這兩種細胞皆在免疫反應中扮演重要的角色。由於樹突細胞的生命週期相當短，所以他們必須不斷地從造血前驅幹細胞分化而來。有趣的是，這些造血前驅幹細胞，包含共同淋巴前驅細胞(common lymphoid progenitor, CLP)會表現不同種類的模式識別受體(pattern recognition receptors)，包括類鐸受體(Toll-like receptors, TLRs)，而這些TLR會辨認病原體上的病原體相關分子模式(pathogen-associated molecular patterns)，以保護宿主免於感染。目前這些造血前驅幹細胞如何對TLR配體做出反應並造成什麼結果還不太清楚。我們先前發現在穩定狀態的時候，CLP在Flt3配體的培養下會主要發育成漿狀樹突細胞，而生成較少的傳統樹突細胞。但是在發炎和感染的狀態時，樹突細胞的發育過程仍不是很了解。在我們的研究中，發現不論是在體內或是體外的R848 (TLR7配體)刺激下，會大幅改變樹突細胞的發育程序，增加傳統樹突細胞並減少漿狀樹突細胞的分化，而這個現象也發生在兩種骨髓系前驅細胞，包括共同骨隨前驅細胞(common myeloid progenitor, CMP)和共同樹突前驅細胞(common dendritic cell progenitor, CDP)，但是相較於CMP和CDP，CLP對於TLR7所誘導樹突細胞發育的改變還要更為敏感。另一方面，除了漿狀樹突細胞和傳統樹突細胞的發育，在R848的刺激下，也會減少第一型傳統樹突細胞(cDC1)的分化，而去增加第二型傳統樹突細胞(cDC2)的分化。除此之外，R848的刺激下會造成漿狀樹突細胞上的sialic acid binding Ig-like lectin H (Siglec-H)的表現量的減少以及CD5的表現量的增加。除了TLR7 ligand外，水疱性口炎病毒(vascular stomatitis virus, VSV)的感染也會造成和R848一樣的結果。更重要的是，從在體內處理過R848的老鼠中分離出CLP和CDP，體外培養後，即使不加R848也會使這兩種前驅細胞產生較多的傳統樹突細胞。野生型及Myd88-/-CLP的共培養實驗中，發現TLR7誘導傳統樹突細胞增加的現象可能是透過主要和次要的TLR7訊息傳導路徑包括完全依賴STAT1及部分依賴第一型干擾素的訊息路徑來達成的。此外，TLR7的訊號會透過對serine磷酸化在727位點的方式來活化STAT1，如果將STAT1上的第727位點的serine突變成alanine，就會部分抑制TLR7促進傳統樹突細胞生成的現象。另一方面，STAT1和第一型干擾素也會調控TLR7所誘導Siglec-H表現降低的現象，但是，只有STAT1會調控TLR7所誘導CD5表現上升的現象，而第一型干擾素則不會參與其中。總結來說，我們發現在發炎及感染狀態下，樹突細胞發育的過程是相當多變的，此外我們也確定了STAT1的serine磷酸化和第一型干擾素在TLR7誘導CLP生成樹突細胞的發育過程的作用機制。

關鍵字

樹突細胞發育 ； 發炎 ； 感染

並列摘要

Dendritic cells (DCs), including plasmacytoid DCs (pDCs) and conventional DCs (cDCs) play an essential role in the immune response. DCs are short-lived and are constantly replenished from hematopoietic stem and progenitor cells (HSPCs). Interestingly, HSPCs including common lymphoid progenitors (CLPs) express different kinds of pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) which sense pathogen-associated molecular patterns (PAMPs) from pathogens and protect hosts from infection. It is still largely illusive whether HSPCs can respond to TLR ligands and what the consequences are following the stimulation. We have previously shown that Flt3 ligand (FL) preferentially promotes the development of pDCs, as opposed to cDCs, from CLPs at steady state. However, the developmental program of DCs during inflammation or infection is unclear. Here, we demonstrate that the administration of R848, a TLR7 agonist, dramatically alters the developmental program by enhancing cDC production at the expense of pDC population in vitro and in vivo, this phenotype is also observed in common myeloid progenitors (CMPs) and common DC progenitors (CDPs), two progenitors of myeloid lineage. CLPs, however, are more sensitive to TLR7-induced reprograming of DC development than CMPs and CDPs. In addition to pDC and cDC, the ratio cDC1 to cDC2, two subsets of cDC, also decreases upon TLR stimulation. Moreover, expression of Siglce-H and CD5, two functional markers of pDC is oppositely regulated by the stimulation. In addition to TLR ligand, VSV infection in vitro also exerts the same effects as R848. More importantly, ex vivo DC developmental potential of CLPs and CDPs from mice previously treated with R848 also prefer cDC generation even though R848 is omitted in the culture condition. Coculture of WT and Myd88-/- CLPs showed that the effect may be dependent on primary and secondary signaling events downstream of TLR7. The mechanism of TLR7-dependent enhancement of cDC generation is mainly STAT1-dependent and partially IFN-I-dependent. Surprisingly, ligation of TLR7 activates STAT1 phosphorylation on serine 727 residues, and mutation of serine to alanine in STAT1 partially blocked TLR-induced cDC formation from CLPs. On the other hand, STAT1 and IFN-I is required for TLR7 signaling-dependent reduction of Siglec-H, while only STAT1, but not IFN-I, is required for higher expression of CD5 during inflammation. In sum, these findings reveal that DC developmental program from their progenitors is very dynamic during inflammation or infection. Moreover, we define a novel function of serine phosphorylation of STAT1 and IFN-I signaling in TLR-mediated reprogramming of DC development from CLPs.

並列關鍵字

dendritic cell development ； inflammation ； infection

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