间充质干细胞移植促进脑梗死神经修复的免疫调节机制研究

Little is known about the mechanism in the treatment of cerebral infarction by mesenchymal stem cells(MSCs) transplantation. Since the survival rates of MSCs after transplantation have been very low, it is very difficult to interpret the clinical efficacy with the well-accepted theory based on neurotrophic effect of MSCs. In recent years, new evidences suggest immune mechanisms participate in the secondary damage after ischemic stroke. Elements of innate and adaptive immunity are engaged in the pathophysiological processes of ischemic stroke. Based on that immunomodulation is one of the most important property of MSCs, it is presumed that the immunomodulation of MSCs plays an important role in the therapy of cerebral infarction. It is hypothesized that the transplantation of MSCs suppress innate immunity which contributes to ischemic brain injury besides their secretion of neurotrophic factors, and the release anti-inflammatory cytokines protect from brain injury in the early phase of ischemic stroke. At the same time, the inhibition of T and B lymphocytes reduces the adaptive immune response against CNS-specific antigens. Neuroprotective influence is obtained through restricting partly on immune and inflammatory response in the chronic phase because of interruption of immune cascade. In support of this hypothesis, we plan to transplant MSCs to the MCAO rats and co-culture MSCs with brain slice of MCAO rats to observe its impact on innate and adaptive immunity and to illustrate the role of immunomodulation of MSCs in the treatment of cerebral infarction. This study discusses the neuroprotective effect of MSCs on the cerebral ischemia from immunological angle and puts forward a viewpoint that immunomodulation is another important mechanism contributing to cerebral infarction thearapy.

间充质干细胞（MSCs）治疗脑梗死作用机制不甚明了。其移植后存活率低，很难完全用公认的神经营养机制来解释疗效。近年来，新证据显示免疫机制参与脑梗死后的病理生理过程，导致继发脑损伤。基于免疫调节作用是MSCs的重要特性，我们推测MSCs的免疫调节机制在脑梗死治疗中起重要作用。我们设想：移植的MSCs在治疗初期，除分泌神经营养因子外，还抑制固有免疫对脑组织的损伤，其分泌的抗炎因子保护了脑组织；同时，MSCs对T、B淋巴细胞的抑制，减少了适应性免疫对自身脑组织的免疫反应。免疫级联反应的打断使颅内远期免疫炎症反应得到部分控制，达到脑保护作用。因此我们拟通过移植MSCs治疗MCAO大鼠及MSCs与MCAO大鼠脑片共培养，观察其对固有免疫和适应性免疫的影响，阐明MSCs的免疫调节机制在治疗脑梗死中的作用。研究从免疫学角度探讨MSCs对脑缺血的保护，提出MSCs的免疫调节作用是治疗脑梗死的又一重要机制。

同种异体MSCs静脉移植治疗SD大鼠脑梗死模型，无论对损伤较重的MCAO模型还是损伤相对较轻的dMCAO 模型，移植细胞都能存在于梗死周边区并散在分布于梗死区内，且能减小脑梗死体积和改善动物行为缺损。就MCAO模型而言，在移植后30天观察期内，没有发现移植组脑内的营养性细胞因子含量高于缺血对照组；但证实了MSCs的免疫抑制作用。包括：（1）超急性期（移植后6小时）有效抑制了脑内多种促炎症细胞因子；（2）急性期（移植后3天）抑制了固有免疫中的单核巨噬细胞, 恢复期（7-30天） 抑制了获得性免疫中的T、B淋巴细胞；（3）从移植后3小时开始到21天，对外周血多种促炎症因子具有抑制作用，特别是抑制了IL-2、IL-6。对于梗死灶较小的dMCAO模型，同种异体MSCs移植后，首先发挥了促炎症作用，表现为MSCs移植组和缺血对照组相比，脑内梗死区、纹状体的炎症反应在2-4天升高，但MSCs促炎作用是一过性的，到移植后4-7天，MSCs还是主要发挥免疫抑制作用。MSCs移植dMCAO模型后，皮层梗死区BDNF在2、4天，IGF-1在2、4、7天都显著高于缺血对照组；纹状体区的IGF-1在移植后第2天也显著高于缺血对照组。染色发现，这些升高的营养因子来自于植入的MSCs细胞、宿主梗死区的神经元以及小胶质/巨噬细胞，后者为主要的来源细胞。细胞计数发现，移植后2天时间点 MSCs显著升高了梗死区IGF-1+CD68+和 BDNF+Iba-1+双阳性细胞的密度。这些结果说明，对于dMCAO模型，至少急性期（2天）MSCs移植还具有明显的营养作用，MSCs产生以及诱导宿主产生的BDNF、IGF-1等营养因子参与了疗效。综上所述，本研究证实了免疫调节机制是MSCs静脉移植脑梗死大鼠产生神经保护的部分原因，对dMCAO模型而言，神经营养作用也是其中机制之一。