M细胞改变在急性肝坏死早期肠粘膜免疫损伤中的作用研究

Mucosal immune injury is an important reason of further liver injury caused by bacterial translocation, however, the initiating mechanisms of mucosal immume injury are not clear now. M cells, considered as the "gateway" to the mucosal immune, play important roles in initiating the mucosal immune system. Our previous work found that intestinal M cells numbers increased in the early stage of acute liver necrosis, and in further research, we discovered that the number of intestinal IgA-positive lymphocytes and and IgA secretion reduced, intestinal mucosa immunity weakened, and intestinal bacteria translocation increased. In recent discoveries, RANKL is found to be closely related with production of M cells, and intestinal mucosa M cell of RANKL knocked out mouse decreased dramatically. This study intends to use RANKL knocked out mice and in vitro cell culture experiment, to detect the variation in quantity of intestinal M cells in the early stage of acute liver necrosis, and impact of M cell variation in intestinal mucosa immune injury, intestinal bacteria translocation and liver injury; to make clear the adjusting function of RANKL signal pathway in the increasing of intestinal mucosa M cells in the early stage of acute liver necrosis; in order to provide new ideas and intervention targets of acute liver injury prevention and treatment.

肠粘膜免疫损伤是肠道细菌移位加剧肝损伤的重要原因，但其发生的始动机制尚不清楚。M细胞被认为是粘膜免疫的"门户"，在粘膜免疫启动中发挥重要作用。我们发现，急性肝坏死早期肠粘膜M细胞数量增加，进一步研究发现肠IgA阳性淋巴细胞数量及sIgA表达减少，肠粘膜免疫削弱，肠道细菌移位增加。RANKL最近被发现与M细胞形成密切相关，RANKL敲除小鼠肠粘膜M样细胞数量锐减，本研究拟利用RANKL敲除小鼠及体外原代细胞培养进行实验，研究急性肝坏死早期肠粘膜M样细胞数量变化以及M样细胞数量改变对肠粘膜免疫损伤、肠道细菌移位及肝损伤的影响，并探索RANKL信号通路在急性肝坏死早期肠粘膜M样细胞增加中的调控作用，为防治急性肝损伤提供新的思路及干预靶点。

本项目在国家自然科学基金的资助下，自 2012 年开始对M细胞改变在急性肝坏死早期肠粘膜免疫损伤的作用进行研究。主要有以下发现：1. 肝衰竭时肠IgA阳性淋巴细胞数量减少以及IgA表达水平降低，致使SIgA分泌合成减少，使其不能在粘膜表面形成完整的SIgA屏障层，从而导致肠源性感染的发生； 2. H2S能够帮助细菌穿透肠屏障，并且这一作用很大部分是通过影响细菌穿透肠道M细胞来实现的；3. 肝衰竭小鼠模型肠组织MAdCAM-1表达明显降低，肠粘膜细胞凋亡比率增加，并与急性肝衰竭时肠道IgA+细胞数以及肠粘膜SIgA表达明显正相关，提示淋巴细胞归巢障碍及肠道细胞凋亡共同参与肝衰竭肠IgA阳性淋巴细胞减少；4. 早期给予LTβR进行干预，能够部分恢复急性衰竭小小鼠肠道IgA+细胞数量及SIgA含量，并且这一干预作用可能是通过增加肠道MAdCAM-1表达来实现的，对肠道淋巴细胞凋亡的保护作用有限。5. 肠道免疫外分泌成分PIgR蛋白表达降低与急性肝衰竭时肠道SIgA表达明显正相关，对我们认识急性肝衰竭肠道免疫损伤的机制提供了新的视角；该研究为进一步明确肝衰竭时肠粘膜免疫损伤的机制以及为今后的临床干预提供新的理论依据。