MICA分子介导的肠上皮细胞在炎症性肠病肠道粘膜免疫中的作用

Inflammatory bowel disease (IBD) is an autoimmune disease characterized by uncontrolled activation of lymphocytes. Breakdown of immune tolerance toward the intestinal contents results in dysregulated and/or constant activation of the immune system. MICA is a stress-induced major histocompatibility complex-related molecule expressed on normal intestinal epithelial cells (IECs) and recognized by the NKG2D-activationg receptor on CD8+ T cells,γδ T cells, and natural killer cells. MIC molecules function as signals of celluar stress and trigger a range of immune effector mechanisms, including cellular cytotoxicity and cytokine secretion. IECs can play a role in the activation of mucosal T cells in IBD by processing antigen.ICEs express surface molecules and restriction elements (classic and nonclassic major histocompatibility complex [MHC] molecules) that allow them to interact with unique subsets of T cells. MICA is restricted to the intestinal epithelium, while their expression is strongly induced in many tissues in response to various pathological conditions including carcinomas, melanomas and certain leukemias, as well as viral and mycobacterial infections. We previously showed that MICA expression can be markedly increased in the ICEs of patients with UC patients. In the present study, we will isolate the intestinal epithelial cells of UC patients,CD patients and controls, and the immune cells as well. Then investigate the expression of cytokins, providing evidence for the role of MICA in the mucosal pathogenesis of UC and to reveal the precise role of abnormalities of mucosal immunity in the pathogenesis of UC.

炎症性肠病是一种自身免疫性疾病，肠上皮屏障驱动的肠粘膜免疫失衡可能是其发病病因之一。目前对肠上皮细胞在炎症性肠病发病中作用的研究集中在肠通透性方面，而探索肠上皮细胞与肠粘膜层中含有的各种免疫细胞之间的关系尚待进行。本项目基于前期工作中发现的溃疡性结肠炎患者肠道上皮细胞表面的MICA分子可能参与溃疡性结肠炎的发病机制，立足于肠上皮屏障与肠道粘膜免疫失衡的基本理论，提出MICA分子可能介导肠上皮细胞与肠道粘膜层天然免疫及获得免疫细胞之间的相互作用，从而成为炎症性肠病肠粘膜免疫触发点这一假设。通过分离获得肠上皮细胞、上皮内淋巴细胞、固有粘膜层淋巴细胞及外周血淋巴细胞并观察MICA配体及各种炎性因子表达量、细胞间杀伤作用等，探讨MICA分子对溃疡性结肠炎和克罗恩病患者肠道局部粘膜免疫的作用。本研究以MICA分子为切入点，从局部粘膜免疫紊乱这一层面为炎症性肠病的诊治提供新的启迪。

炎症性肠病是一种自身免疫性疾病，肠上皮屏障驱动的肠粘膜免疫失衡可能是其发病病因之一。本项目旨在论证MICA分子可能介导肠上皮细胞与肠道粘膜层天然免疫及获得免疫细胞之间的相互作用，从而成为炎症性肠病肠粘膜免疫触发点这一假设。通过分离获得肠上皮细胞、上皮内淋巴细胞、固有粘膜层淋巴细胞及外周血淋巴细胞并观察MICA配体及各种炎性因子表达量、细胞间杀伤作用等，探讨MICA分子对溃疡性结肠炎和克罗恩病患者肠道局部粘膜免疫的作用。.通过流式细胞术分析发现，与正常对照组相比，溃疡性结肠炎患者肠道固有层中CD3+NKG2D+T细胞（48.92%±6.374% vs 32.03% ±5.146% ；P＜0.05）及CD4+NKG2D+T细胞（20.20%±3.716% vs 11.80% ±3.907% ；P＜0.05）均明显升高。研究提示，NKG2D高表达于溃疡性结肠炎患者中，其中表达NKG2D受体的T细胞可能参与了溃疡性结肠炎的发病。而在表达NKG2D受体的T细胞中，可能以CD4+NKG2D+T细胞为主。而CD组患者与正常组相比无统计学差异（35.60%±6.793% vs 25.60% ±5.892% ；P＞0.05）。.通过将MICA抗体封闭后的肠道上皮细胞与T细胞共培养后的细胞杀伤实验发现，MICA抗体封闭后的肠道上皮细胞增殖活性明显降低。同时，RT-qPCR实验提示，IFN-γ与IL-17在UC组肠粘膜固有层淋巴细胞中显著上调，与正常对照组相比具有显著性差异（P＜0.001）。而IL-4在UC组肠粘膜固有层淋巴细胞中下降，与正常对照有差异，但不具有显著性差异（P＞0.05）.通过上述结果可以初步推论：.1. MICA分子在UC患者中较正常人表达明显增多，MICA参与免疫反应。.2. UC患者LPMCs中，NKG2D+T细胞较正常人表达上调，且以CD4+NKG2D+T细胞为主，CD8+NKG2D+T细胞与正常人无明显差异。提示可能CD4+NKG2D+T细胞在UC发病中起免疫调节的作用。.3. 肠上皮表面的MICA分子与T细胞表面的NKG2D相互识别，参与UC的发病。推测MICA-NKG2D相互是肠道上皮细胞参与IBD肠道炎症的关键靶点。.4. IFN-γ与IL-17参与了UC的发病，推测IFN-γ与IL-17在UC发病过程中主要发挥促炎作用。