渗入脑内的免疫球蛋白G与外周脂多糖引起大鼠脑内Toll样受体4的表达

Expression of Toll-like receptor 4 induced by extravasated IgG and peripheral LPS in rat brains

目的探讨从血循环中渗入到脑内的自体内源性免疫球蛋白G(IgG)对外周脂多糖(LPS)刺激引起的中枢神经系统内Toll样受体4(TLR4)表达的作用。方法将SD大鼠20只随机分为4组,每组5只。LPS+生理盐水组:腹腔注射LPS100μg/kg,6h后尾静脉给予生理盐水15μg/kg;AD组:尾静脉给予盐酸肾上腺素(AD)15μg/kg;LPS+AD组:先腹腔给予LPS,6h后静脉注射AD;对照组大鼠静脉注射生理盐水作为对照。最后一次注射后30min处死动物,取脑,分别用免疫荧光染色和RT-PCR方法检测脑内TLR4的表达。结果免疫荧光染色显示,单独给予AD的动物中IgG免疫阳性产物呈斑片状分布于脑实质。LPS+生理盐水组的IgG免疫阳性产物仅限于血管周围;在LPS+AD组,IgG渗出区域内可见TLR4免疫阳性产物与小胶质细胞标志物Iba-1共存,双标的细胞分散于脑实质及血管附近,而LPS+盐水组TLR4阳性细胞呈内皮细胞样。RT-PCR结果显示,LPS+AD组TLR4的表达显著高于LPS+生理盐水组、AD单独注射组以及生理盐水对照组。结论大鼠血循环中的IgG渗入脑内可促进外周LPS引起的脑内TLR4表达。

Objective To investigate the effect of immunoglobulin G （IgG） extravasated from blood circulation on the expression of tolllike receptor 4 （TLR4） induced by peripheral lipopolysaccharide （LPS） in rat brain. Methods The rats were divided into four groups in random, 5 rats in each. Group one received LPS 100μg/kg by intraperitoneal administration, normal saline was given by intravenous injection 6 hours later; group two was injected with adrenalin （AD） 15μg/kg intravenously; group three was treated with LPS intraperitoneally, AD was injected 6 hours later; group four was injected normal saline intravenously as control. For all groups, the animals were sacrificed 30 min after the last injection, and the brains were taken for investigation of the TLR4 expressions by immunofluorescence staining and RT-PCR. Result Immunofluorescence staining showed that IgG immunoreactive product was patchlike, distributed in the brain parenchyma in all the animals that received AD. In the LPS＋normal saline group, IgG was found merely around the blood vessels. Meanwhile, in LPS＋AD animals, TLR4 immunoreactive product coexisted with microglia marker Iba-1 within the IgG extravasated area. The double-labeled cells dispersed in the brain parenchyma and near to the cerebral vessels. In the LPS＋saline group, TLR4 positive cells were endotheliallike RT-PCR results indicated that the expression level of TLR4 in the LPS＋AD group were significantly higher than that in the LPS＋saline group or AD group or the saline control （P 〈0.01）. Conclusion Extravasated circulating IgG may enhance the TLR4 expression in the rat brain induced by peripheral LPS.