摘要
TRAIL(TNF-related apoptosis-inducing ligand)是一個屬於TNF家族的第二型胯膜蛋白 (type II transmembrane protein)，可藉由與TRAIL受體(TRAIL-R)作用而引發細胞凋亡。在免疫系統中，TRAIL表現在多數已活化的免疫細胞上，包含自然殺手細胞、 NKT細胞、單核細胞 (monocytes)、樹突狀細胞 (DCs), 巨噬細胞(macrophage), T細胞和B 細胞。 除了引發細胞凋亡，研究也發現TRAIL可能參與自體免疫的調控。在一些自體免疫疾病的動物模式，如實驗性自體免疫腦炎 (EAE )和鏈脲佐菌素誘導糖尿病(Streptozotocin-induced diabetes)中，TRAIL-/-小鼠有更嚴重的發炎。除此之外，我們實驗室的初步研究發現，在膠原蛋白誘發類風濕性關節炎 (collagen induced arthritis；CIA)的中，注射TRAIL重組蛋白能顯著降低發炎症狀，並能夠抑制T細胞的活化。基於這些發現，我們想研究TRAIL在其他自體免疫疾病中的角色。 發炎性大腸疾病(Inflammatory bowel disease；IBD) 是一個由於免疫變化，導致了患者對失去對腸道內共生菌的免疫耐受性(immune tolerance)，或是影響腸道的功能而造成的大腸發炎之自體免疫疾病。雖然TRAIL在IBD致病機轉中的角色仍不明確，但有研究指出TRAIL-R-/-小鼠在DSS誘發腸炎的動物模式中，表現出更嚴重的腸炎，而且T細胞在此模型中的重要性也有被探討過。因此我們使用DSS誘發腸炎的模型來研究TRAIL在腸道發炎中的角色。 在這篇研究中，我們發現注射TRAIL到DSS誘發大腸炎小鼠體內，會顯著降低體重下降、大腸長度減短、腸道發炎和腸道上皮層損傷的程度，這些結果暗示TRAIL可能有抑制發炎反應的功能。然而，分析腸道內細胞之促發炎細胞激素和抗發炎細胞激素的表現量，卻發現兩者都被顯著抑制，因此TRAIL有可能是作用在抑制T細胞的活化，因為它們是IBD中細胞激素的重要來源。 另一方面，利用TRAIL-R-/-小鼠，我們發現TRAIL無法在TRAIL-R-/-小鼠中 呈現腸道發炎的保護作用，顯示出TRAIL的保護功能必須透過和TRAIL-R作用。進一步的研究發現，TRAIL和TRAIL-R結合並不會誘導小鼠的T細胞或是大腸組織中其他細胞的凋亡，反而具有抑制T細胞活化的效用。此研究不但發現在IBD致病機轉中TRAIL抑制T細胞活化之重要性，同時也助於發展新的IBD治療方式。
關鍵字
發炎性腸炎並列摘要
TRAIL (TNF-related apoptosis-inducing ligand) is a type II transmembrane protein that belongs to TNF family, and it can induce apoptosis through binding with TRAIL receptor (TRAIL-R). TRAIL is widely expressed on activated immune cells, including NK cells, NKT, monocytes, DCs, T cells and B cells. Apart from inducing cell apoptosis, reports have suggested that TRAIL may play a role in regulation of autoimmunity. In autoimmune disease animal models such as EAE (experimental autoimmune encephalomyelitis) and streptozotocin (STZ) -induced diabetes, TRAIL-/- mice suffered more severe inflammation and accelerated pathogenesis. Moreover, our preliminary results showed that injection of recombinant TRAIL significantly reduced the severity of inflammation and may suppress the activation of T cell in CIA (collagen induced arthritis) mice. Based on these findings, we would like to investigate the role of TRAIL on other autoimmune disease. Inflammatory bowel disease (IBD) is an autoimmune disease caused by immune dysregulation, which leads to defective host immune tolerance toward commensal intestinal microbiota, and effects on intestinal epithelial barrier function. Although the role of TRAIL in IBD pathogenesis remained unclear, it has been reported that TRAIL-R-/- mice suffered more severe colitis in DSS-induced colitis, a widely use experimental IBD model. In addition, the importance of T cell in the pathogenesis of DSS-induced colitis has been well addressed. Therefore, we applied DSS-induced colitis to investigate the role of TRAIL in inflammatory colitis. Injection of recombinant TRAIL into DSS colitis mice significantly reduced DSS-induced weight loss, colon inflammation and epithelial damage. These result implied that TRAIL may promote anti-inflammatory response. However, the expression of both pro-inflammatory and anti-inflammatory cytokines are significantly down-regulated in colon tissue, suggesting that TRAIL may have direct effects on T cells. On the other hand, we found that the protective function of TRAIL was abolished in TRAIL-R-/- mice, indicating the therapeutic effect of TRAIL is dependent on the interaction with TRAIL-R. Further studies showed that TRAIL/TRAIL-R did not trigger apoptosis of either T cells or other cells in the colonic tissue, but suppressed the activation of T cells instead. Here we found that TRAIL plays an important role in IBD pathogenesis through suppressing the activation of T cells, and it may also provide a new potential therapeutic strategy for IBD.
參考文獻
延伸閱讀
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