细颗粒物暴露对大鼠肺脏清除肺炎克雷伯菌的影响

Effects of PM2.5 exposure on Klebsiella pneumoniae clearance in the lungs of rats

目的 探讨细颗粒物（PM2.5）暴露对大鼠肺炎克雷伯菌感染易感性和细菌清除率的影响及其机制.方法 86只雄性SD大鼠采用随机数字表法分为4组：空白对照组（16只）、肺炎克雷伯菌感染组（感染组,20只）、PM2.5组（PM组,20只）和PM2.5＋肺炎克雷伯菌组（混合组,30只）；分别给予肺炎克雷伯菌、PM2.5暴露及PM2.5暴露＋肺炎克雷伯菌,建立大鼠模型,并于第1天和第7天时处死,进行一般状态临床评分,计算各组总死亡数,进行BALF中细菌培养及鉴定并计算各组肺炎克雷伯菌感染率,观察大鼠肺脏病理变化、炎症分级,用ELISA方法测定血清中IL-6和肿瘤坏死因子（TNF）-α的含量,显微镜下计数BALF中的细胞数,并在扫描电镜下观察气管黏膜的变化.结果 混合组第7天时的总死亡数为14只,显著高于对照组（0）、感染组（4只）和PM组（4只）.混合组肺炎克雷伯菌的检出数为13只,显著高于感染组（6只）.混合组第1天和第7天BALF中白细胞数分别为（11.96±0.56）×105/L和（15.68 ±0.81）×105/L,中性粒细胞数分别为（5.76±0.44）×105/L和（9.41 ±0.64） ×l05/L,均显著高于对照组、感染组和PM组.混合组肺组织病理炎症改变较感染组、PM组和对照组严重.混合组第1天和第7天时血清中TNF-α含量分别为（829±90） ng/L和（1055 ±91） ng/L,IL-6含量分别为（1.26±0.16）和（1.95±0.18） ng/L,均显著高于对照组,且第1天的TNF-α含量与第1天和第7天的IL-6含量显著高于感染组[第1天TNF-α含量为（576±133） ng/L,第1天和第7天的IL-6含量分别为（0.82±0.17）和（1.26±0.29） ng/L]和PM组[第1天TNF-α含量为（400 ±67） ng/L,第1天和第7天的IL-6含量分别为（0.40 ±0.10）和（0.55±0.17） ng/L].扫描电镜示PM组大鼠气管黏膜纤毛杂乱、粘连、成束分布、变短、不规则或脱落.结论 PM2.5暴露可增加大鼠对肺炎克雷伯菌感染的易感性,降低细菌的清除率,加重感染所致的肺脏炎症反应,其机制可能与气管的黏液纤毛系统功能受损及炎症因子的相互作用有关.

Objective To investigate the effects of PM2.5 exposure on susceptibility to Klebsiella infection and bacterial clearance,and to discuss its possible mechanisms.Methods Eighty-six healthy male SD rats were randomly divided into 4 groups：a control group,a Klebsiella pneumoniae infection group （infection group）,a PM2.5 group and a PM2.5 ＋ Klebsiella pneumoniae infection group（combined group）We developed a rat model in which the animals were given Klebsiella pneumoniae,PM2.5 exposure and PM2.5 exposure followed by infection with Klebsiella pneumoniae respectively.The clinical scores were evaluated.The total mortality of each group was assessed.Bacterial load in the BALF was quantified and the infection rate of each group was assessed.Lung histopathological changes were detected by HE staining.The concentrations of IL-6 and TNF-α in serum were detected by ELISA.Cells in the BALF were counted for each group by microscopy.The changes of tracheal membrane epithelial cells were observed by scanning electron microscope.Results The total mortality in the combined group （n =14） was higher than that in the control group （n =0）,infection group （n =4） and PM2.5 group （n =4）.The infected cases in the combined infection group （n =13） was higher than that in the infection group （n =6）.The total number of WBC in BALF in the combined group on the first day [（11.96 ± 0.56） × 105/L] and seventh lay [（15.68 ±0.81） × 105/L] was higher than that in the control group,the infection group and the PM2.5 group.The neutrophil number in BALF in the combined group on the first day[（5.76 ±0.44） × 105/L] and seventh day[（9.41 ±0.64） × 105/L] was higher than that in the control group,the infection group and the PM2.5group.The lung pathological changes were much more severe in the combined group as compared to those in the control,the infection and the PM2.5 groups.Concentrations of TNF-α in serum in the combined group on the first day[（829±90） ng/L] and the seventh day[（1055 ±91） ng/L] were higher than those in the control group and the PM2.5 group.Concentrations of IL-6 in serum in the c ombined group on the first day [（1.26 ±0.16） ng/L] and seventh day[（1.95 ±0.18） ng/L] was higher than those in the control,the infection and the PM2.5 groups.Tracheal cilia in the PM2.5 group showed signs of disorderly arrangement,adhesion and eeclasis.Conclusions PM2.5 exposure increased the susceptibility of the rats to Klebsiella pneumoniae infection and decreased bacterial clearance.Its mechanism may be related to impairment of the bronchial mucociliary system and interaction of cytokines.