第二類CD1d分子限制型自然殺手細胞的生長發育機制及其導致自體免疫性腸炎的探討

THE DEVELOPMENTAL REQUIREMENTS AND FUNCTIONS OF CD1D-RESTRICTED TYPE II NATURAL KILLER T (NKT) CELLS AND THEIR ROLES IN THE PATHOGENESIS OF INFLAMMATORY BOWEL DISEASE

廖家敏(Chia-Min Liao)

指導教授 ： 于宏燦

共同指導教授 ： 王瓊如(Chyung-Ru Wang)

國立臺灣大學/生命科學院/動物學研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.00238

摘要

CD1d分子限制型自然殺手T細胞(Natural killer T cells)為一群具有免疫調節功能的細胞。依照T細胞受體(T-cell receptor)的基因表現，此類細胞可歸於於兩大類：第一類與第二類CD1分子限制型自然殺手T細胞。第一類CD1d分子限制型自然殺手T細胞表達固定的T細胞受體，並且可以四聚體(GalCer/CD1d)檢測。反之，第二類CD1d分子限制型自然殺手T細胞表達多樣的T細胞受體，而目前為止並無專一的方法偵測此類細胞。有別於傳統的T細胞， 第一類CD1d分子限制型自然殺手T細胞的生長發育是由 CD1d表達的造血幹細胞負責。此外，淋巴細胞訊息活化分子(SAP)也被證明是對第一類CD1d分子限制型自然殺手T細胞的生長發育與功能有重要的調節作用。以目前的研究發展和規範，多針對第一類CD1d分子限制型自然殺手T細胞有所了解，而對第二類的CD1d分子限制型自然殺手T細胞的生長發育機制與其在臨床疾病上所扮演的角色所之甚少。第一類CD1d分子限制型自然殺手T細胞在自發性腸炎的小鼠模型中具有複雜的角色，而臨床研究中在潰瘍性結腸炎腸道炎症的病患中發現第二類CD1d分子限制型自然殺手T細胞似乎具有更重要的影響力。因此，本研究利用轉基因小鼠(24αβTg)來探討第二類的CD1d分子限制型自然殺手T細胞的生長發育。利用骨髓轉移的技術，我證明了第二類的CD1d分子限制型自然殺手T細胞的生長發育亦是由CD1d表達的造血幹細胞負責。由於此兩類細胞具有相似的生長選擇機制，我更進一步研究淋巴細胞訊息活化分子是否對第二類CD1d分子限制型自然殺手T細胞也有所影響。藉由雜交轉基因小鼠至淋巴細胞訊息活化分子缺陷型小鼠中，我觀察到第二類的CD1d分子限制型自然殺手T細胞具有不成熟的表型，及受損的細胞分子 IFN-γ 和 IL-4表現。而此細胞因子的缺失更與轉錄因子T-bet和Eomes有顯著的相關。此外，為了探討第二類的CD1d分子限制型自然殺手T細胞和過量表達CD1d分子所引起的失衡是否會對此細胞的生長發育造成影響，亦或會導致自發性腸炎。我便雜交轉基因小鼠與CD1d分子過量表達的小鼠。在此雙重轉基因的小鼠中，我觀察到第二類的CD1d分子限制型自然殺手T細胞的數量減少。此項結果證明了過量表達自身抗原或自配體，如CD1d分子，會引起胸腺負選擇機制並導致第二類的CD1d分子限制型自然殺手T細胞的計畫性死亡。利用轉移細胞到免疫缺陷型小鼠的方法，我更進一步直接證明了第二類的CD1d分子限制型自然殺手T細胞在CD1d分子過量表達的背景下發展出的致病性。總體來說，本研究首次證明了第二類CD1d分子限制型自然殺手T細胞的生長發育是由CD1d表達的造血幹細胞負責，並提供了淋巴細胞訊息活化分子在調節此類細胞的正長生長發育與成熟表型的證據。此外，此研究並證明了異常的第二類CD1d分子限制型自然殺手T細胞反應會導致自發性腸炎，更突顯出了CD1d的表達水平與第二類CD1d分子限制型自然殺手T細胞的發展和其在免疫系統中的重要性。

關鍵字

自然殺手細胞 ； 自發性腸炎 ； CD1d

並列摘要

CD1d-restricted NKT cells are a unique subset of immunoregulatory T cells
further divided into two subtypes. Type I NKT cells express semi-invariant TCR and can be detected using α-GalCer/CD1d tetramer, whereas type II NKT cells express diverse TCR and cannot be directly identified. The developmental requirements and molecular mechanisms that regulate type I NKT cells are distinct from those of conventional T cells. CD1d-expressing hematopoietic cells are shown to be required for mediating the positive selection of type I NKT cells. In addition, signaling lymphocytic activation molecule-associated protein (SAP) is an adaptor molecular which has also been shown to be important for the development and function of type I NKT cells. Unlike type I NKT cells which have been well investigated, studies of the development and mechanisms of which regulate type II NKT cells are poorly understood. Furthermore, clinical studies on several mouse models of inflammatory bowel disease (IBD) have revealed a complex role for type I NKT cells in the development of IBD while type II NKT cells appear to contribute to intestinal inflammation in individuals suffering from ulcerative colitis. In this study, I used a TCR transgenic mouse model (24αβTg) to study a dominant type II NKT cell population. I demonstrate that the CD1d-expressing hematopoietic cells meditate the efficient selection of type II NKT using bone marrow chimeras. Given the similar developmental requirements sharing between type I NKT and type II NKT cells, I sought to address whether SAP is also required for the development and function of type II NKT cells. Therefore, I generated 24αβTg/SAP-/- mice and observed that type II NKT cells have an immature phenotype and impaired cytokine IFN-γ and IL-4 production in the thymus. The reduction of IFN-γ in type II NKT cells is correlated with a significantly reduced expression of T-bet and Eomes transcription factor. Furthermore, to address whether the dysregulation of type II NKT cells caused by increased CD1d expression can contribute to the pathogenesis of IBD, I crossed 24αβTg mice with CD1Tg mice that express higher levels of CD1d in all cell types. In CD1dTg/24αβTg mice, I observed reduced 24αβT cell numbers, suggesting that type II NKT cells undergo enhanced negative selection when engaged by abundant self-antigen or self-ligands. Additionally, the residual 24αβT cells in CD1dTg/24αβTg mice exhibited an altered surface phenotype and acquired a cytokine profile distinct from that of equivalent cells in 24αβTg mice. Interestingly, CD1dTg/24αβTg mice spontaneously developed IBD and adoptive transfer experiments confirmed that type II NKT cells that develop in the context of increased CD1d expression are pathogenic. Collectively, these findings comprise the first evidence of the CD1d-expressing hematopoietic cells in mediating the selection of type II NKT cells and reveal the pivotal role of SAP in regulating the normal development and mature phenotype and function of type II NKT cells. In addition, I have demonstrated that aberrant type II NKT cell responses directly contribute to intestinal inflammation, highlighting the importance of CD1d expression level in the development and regulation of type II NKT cells.

並列關鍵字

NKT cells ； IBD ； CD1d

參考文獻

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