目的 观察骨髓间充质干细胞(BMSCs)对大鼠硅沉着病（矽肺）纤维化形成的影响，并初步探讨其机制。方法 体外分离、培养BMSCs。将54只健康雌性SD大鼠随机分为生理盐水对照组、硅沉着病模型组、干细胞移植组，每组18只。分别在造模后1、3、7、14、28及56d处死各组大鼠，HE染色观察肺组织形态变化；Masson染色观察胶原增生情况；免疫荧光双标技术检测性别决定基因(sry)和肺泡表面活性蛋白C(SP-C)示踪雄性大鼠BMSCs在雌性硅沉着病大鼠肺组织内的分布及分化情况；免疫印迹法检测肿瘤坏死因子-α(TNF-α)及基质金属蛋白酶-9（MMP-9）蛋白表达情况。结果 HE及Masson染色显示，细胞移植组大鼠肺组织肺泡炎、肺纤维化程度及胶原面积均轻于模型组。免疫荧光双标显示，细胞移植组的雌性大鼠肺组织中有sry阳性的细胞，并且部分sry阳性细胞同时表达SP-C。免疫印迹法结果显示，模型组肺组织TNF-α和MMP-9的蛋白表达均较对照组增高(P ＜0.05)，不同时间点在肺组织内的表达有不同的特点；BMSCs移植组肺组织TNF-α和MMP-9的蛋白表达在各时间点均低于模型组，高于对照组，差异均有统计学意义(P ＜0.05)。结论 BMSCs可以减轻二氧化硅（SiO₂）所致的大鼠硅沉着病纤维化程度，可能与其在肺组织中分化为Ⅱ型肺泡上皮细胞，降低肺组织中TNF-α和MMP-9的蛋白表达有关。

Objective To study effects of bone marrow mesenchymal stem cells on pulmonary silicosis, and to explore its mechanism. Methods BMSCs were harvested from 3-6 week old male SD rats. Fifty-four healthy female SD rats were randomly divided into saline control group, model group and BMSCs transplantation group, 18 in each group. The rats were sacrificed on day 1, 3, 7, 14, 28 and 56 after pulmonary silicosis was induced in the animals. The morphology changes and collagen deposition of lung tissues were investigated by HE staining and Masson staining. The expression of sex-determining gene (sry) and surfactant protein-c (SP-C) were detected by double-immunofluorescence labeling. Western blotting estimated the expression of TNF-α and MMP-9 in lung tissues. Results HE staining and Masson staining showed that alveolitis, pulmonary fibrosis and collagen area of lung tissue in BMSCs transplantation group significantly decreased as compared with that of the control and model groups. Sry positive cells were observed in the lungs tissue from BMSCs transplantation group, and some of sry positive cells also expressed SP-C, the marker of type II pneumocytes. The level of TNF-α and MMP-9 in the model group was significantly higher than that in the control group(P ＜0.05), and had different characteristics at different time points. At the corresponding time, the level of TNF-α and MMP-9 in BMSCs transplantation group was significantly lower than that in the model group(P＜0.05)，higher than that in the control group (P＜0.05). Conclusion BMSCs differentiate into type II pneumocytes and downregulate the expression of TNF-α and MMP-9, which may explain why BMSCs transplantation improves the SiO₂ induced fibrosis.