NLRP3炎症小体在小鼠甲型流感病毒感染继发MRSA肺炎中的表达变化

Activity of NLRP3 inflammasome in MRSA pneumonia secondary to influenza A virus infection in mice

目的:探索NLRP3炎症小体在小鼠甲型流感病毒(甲流病毒)HIN1感染继发耐甲氧西林金黄色葡萄球菌(MRSA)肺炎中的表达变化。方法:选取C57BL/6小鼠15只,分为空白对照组、MRSA组(MRSA滴鼻感染24 h)和H1N1+MRSA组(甲流病毒H1N1滴鼻预感染6 d后联合MRSA滴鼻感染24 h)。检测小鼠肺组织NLRP3和caspase-1的mRNA及蛋白表达水平,并检测白细胞介素1β(IL-1β)在肺组织中的mRNA水平及在血清中的浓度。观察小鼠肺组织病理并分析小鼠IL-1β血清浓度与体重下降率的相关性。结果:MRSA组NLRP3和caspase-1的mRNA及蛋白表达水平与空白对照组比均无明显差异(P>0.05),但IL-1β的mRNA表达水平及血清浓度均明显高于空白对照组(P<0.01)。H1N1+MRSA组NLRP3、caspase-1的mRNA及蛋白表达水平,及IL-1β的mRNA表达水平和血清浓度均明显高于空白对照组(P<0.01)。H1N1+MRSA组NLRP3和caspase-1的mRNA及蛋白表达水平均明显高于MRSA组(P<0.01),但IL-1β的mRNA表达水平及血清浓度均明显低于MRSA组(P<0.01)。MRSA组肺组织病理呈炎症改变,H1N1+MRSA组肺组织病理改变较MASA组更严重。MRSA组及H1N1+MRSA组小鼠体重下降率与IL-1β血清浓度均成负相关(P<0.05)。结论:MRSA感染引起IL-1β的产生和释放不依赖NLRP3炎症小体,而甲流病毒预感染虽然激活了NLRP3炎症小体,但总体降低了机体抗MRSA免疫的IL-1β的表达及分泌,该效应可能是继发于甲流病毒感染的MRSA肺炎更为严重的机制之一。

AIM:To evaluate the activity of NLRP3 inflammasome in methicillin-resistant Staphylococcus aureus(MRSA)pneumonia secondary to influenza A virus(IAV)HIN1 in mice.METHODS:Pneumonia model caused by intranasal inoculation with only MRSA for 24 h(MRSA group)and with MRSA for 24 h secondary to IAV H1N1 infection for 6 d in advance(H1N1+MRSA group)in C57BL/6 mice were established.The mRNA expression of NLRP3,caspase-1 and interleukin-1β(IL-1β)in lung tissues was detected by RT-qPCR.The protein levels of NLRP3 and caspase-1 in the lung tissues were determined by Western blot.The serum concentration of IL-1β was measured by ELISA.The pathological changes of the lung tissues were examined.The correlation between rate of weight loss during infection and serum concentration of IL-1β was investigated.RESULTS:In MRSA group,the mRNA levels and relative protein expression levels of NLRP3 and caspase-1 showed no difference compared with control group(P>0.05),while the mRNA expression of IL-1β and the serum concentration of IL-1βwere significantly higher than those in control group(P<0.01).In H1N1+MRSA group,the mRNA levels and relative protein expression levels of NLRP3 and caspase-1 were significantly higher than those in control group,as well as higher than those in MRSA group(P<0.01),the mRNA level and serum concentration of IL-1β were significantly higher than those in control group but lower than those in MRSA group(P<0.01).The pathological obser vation of the lung in MRSA group showed inflammatory responses,and severer pneumonia in H1N1+MRSA group was found.The rate of weight loss in the mice of MRSA group and H1N1+MRSA group was negatively correlated with the serum concentration of IL-1β.CONCLUSION:IL-1βexpression induced by MRSA infection is in a NLRP3 inflammasome inde pendent manner.It also suggests that IAV H1N1 infection in advance down regulates the expression of IL-1β in secondary infection with MRSA,which may contribute to the mechanism of MRSA pneumonia secondary to IAV infection.