中文摘要：

[目的]研究清热消炎中草药淡竹叶中异荭草苷的体内外抗病毒活性,并初步探讨其作用机制.[方法]采用MTT法测定异荭草苷的细胞毒性,并以异荭草苷的最大无毒浓度为起始浓度,采用空斑减数法测定其体外抗RSV活性,计算其抗病毒的选择性指数（SI值）;继而采用空斑减数法,研究异荭草苷对RSV复制周期不同阶段的影响,采用实时定量PCR法,检测异荭草苷对病毒蛋白mRNA合成的影响;选取3周龄BALB/c雄性小鼠研究异荭草苷体内抗RSV活性,小鼠灌胃给药4d,经鼻腔滴入RSV病毒液造模,继续灌胃给药3d,取小鼠肺组织称重、切片、HE染色,显微镜下观察肺组织病理性改变,并用空斑减数法检测小鼠肺组织内病毒含量.[结果]异荭草苷体外抑制RSV A2株和LONG株的IC50分别为（3.6±0.8）μg/mL和（2.4±0.2） μg/mL,比阳性药利巴韦林的活性略低,因异荭草苷的细胞毒性比利巴韦林小,其抗RSV的选择性指数（SI）为利巴韦林8.3倍;初步的作用机制研究表明,异荭草苷主要抑制RSV在宿主细胞内的复制过程,也可一定程度地抑制病毒进入宿主细胞,实时定量PCR结果显示,异荭草苷可以不同程度地降低RSV的L、F和P蛋白对应的mRNA的表达;异荭草苷可降低小鼠肺组织的病毒滴度,且可缓解病毒引起的炎症.[结论]清热消炎中药淡竹叶中的异荭草苷,具有较好的体内外抗病毒活性,且能一定程度缓解病毒性炎症;该化合物主要在病毒进入宿主细胞后的复制阶段（复制晚期）起作用,能抑制与病毒复制晚期相关的L、F和P蛋白的mRNA表达.

英文摘要：

[Objective] To research the in vitro and in vivo anti-RSV activity of isoorientin isolated from the leaves of Lophatherum gracile Brongn,a traditional Chinese medicine （TCM） used for the treatment of fever and inflammation,and the preliminary mechanism of isoorientin against RSV infection.[Methods] MTT （3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide） assay was adopted to evaluate the cytotoxicity of isoorientin.The anti-RSV activity of isoorientin against A2 and Long strains was investigated by plaque reduction assay.Plaque reduction assay was also performed to evaluate the inhibitory effect of isoorientin on the extracellular and intracellular stages of RSV replication cycle,as well as the inhibitory effects of isoorientin on viral penetration.Quantitative real-time PCR assay was conducted to determine mRNA expression of RSV proteins relating to RSV intracellular replication.Male BALB/c mice of 3 week old were used to evaluate the anti-RSV activity of isoorientin in vivo.Mice were lightly anesthetized with diethyl ether then intranasally challenged with RSV Long strain at 4th day after isoorientin treatment.Isoorientin was continuously treated by intragastric administration for 3 days.The mice were sacrificed,and its lungs were removed,weighed and fixed with methanol for H＆E staining.The viral loads in the lungs were tested by plaque reduction assay.[Results] Isoorientin could dose-dependently inhibit the RSV-induced plaque formation on HEp-2 cells and the IC50 values against RSV A2 and Long strains were （3.6 ± 0.8）μg/mL and （2.4 ± 0.2）μg/mL,respectively,which were almost equal to that of ribavirin.But isoorientin showed lower cytotoxcity with much higher selectivity index （SI） values than that of ribavirin.The preliminary investigation on anti-RSV mechanism showed that isoorientin mainly inhibited replication of RSV at the stage of intracellular,even though it slightly stopped RSV from penetrating into the host infection at the stage of extracellular.Moreover,quantitative