Role of cytokines in the lesion repair in the central nervous system

为了解细胞因子在中枢神经系统（CNS）损伤修复过程中的作用，采用竞争性PCR方法，对实验性自身免疫性脑脊髓炎（EAE）大鼠进行诱导，定量检测中枢神经系统（CNS）促炎性和抗炎性细胞因子mRNA的表达水平。在EAE中，TNF-α和IFN-γ mRNA主要在疾病早期检测到，而抗炎细胞因子之一TGF-β1在疾病晚期达到峰值。下一步，我们研究了自身免疫性炎症期间中枢神经系统中细胞因子与细胞因子受体结合后激活的转导分子STAT（信号换能器和转录激活因子）mRNA和蛋白的动力学和定位。结果表明，STAT4在小胶质细胞中表达，可能被IL-12激活，具有促炎作用；STAT3在整个疾病过程中被激活，主要在星形胶质细胞中表达，似乎作为抗炎信号的传感器。最后，我们进行了原位杂交，以确定在中枢神经系统中产生细胞因子的细胞。由于中枢神经系统中细胞因子的含量较低，因此需要特别注意提高非放射性同位素杂交中使用的探针的灵敏度。通过这一改进，可以证明小胶质细胞表达TNF-α，而神经元和星形胶质细胞表达TGF-β1。综上所述，本文提出了区域修复的机制。自反应性T细胞浸润中枢神经系统后不久，小胶质细胞被T细胞激活，分泌TNF-α等促炎细胞因子上调T细胞功能，同时刺激星形胶质细胞分泌TGF-β等抗炎细胞因子下调炎症过程。由不同类型的脑细胞调节的细胞因子网络对中枢神经系统的区域修复至关重要。

To know the role of cytokines in the lesion repair process in the central nervous system (CNS), experimental autoimmune encephalomyelitis (EAE) was induced in rats and the level of pro- and anti-inflammatory cytokine mRNA in the central nervous system (CNS) was quantitated by competitive PCR. In EAE, TNF-α and IFN-γ mRNA were detected mainly at the early stage of the disease, while one of anti-inflammatory cytokines, TGF-β1, peaked at the later stage.In the next step, we investigated the kinetics and localization of STAT (signal transducer and activators of transcription) mRNA and protein, which is known as a transducing molecule activated after cytokine binding to the cytokine receptor, in the CNS during autoimmune inflammation. It was demonstrated that STAT4 which was expressed in microglia and probably activated by IL-12 plays a pro-inflammatory role and that STAT3 which was activated throughout the disease course and expressed mainly in astrocytes seems to serve as a transducer of anti-inflammatory signals.Finally, we have performed in situ hybridization to determine the cell that produce the cytokine in the CNS. Since the amount of cytokines in the CNS is low, special care was taken to improve the sensitivity of the probe used in non-radioisotopic hybridization. With this improvement, it was possible to show that microglia express TNF-α while neuron and astrocytes express TGF-β1.Taking all these findings together, the following mechanism of the region repair is suggested. Soon after the infiltration of autoreactive T cells in the CNS, microglia are activated by T cells and secrete pro-inflammatory cytokines such as TNF-α to upregulate T cell function and at the same time stimulate the astrocyte which downregulate the inflammatory processes by secreting anti-inflammatory cytokines including TGF-β. The cytokine network regulated by various types of brain cells is critical for the region repair in the CNS.