嗜线虫肠杆菌抑制大蜡螟幼虫的免疫反应

Inhibition of the immune response of galleria mellonellalarvae invaded by Xenorhabdus nematophilus

为探究嗜线虫肠杆菌对大蜡螟幼虫的致病机理,测定被嗜线虫肠杆菌侵入的大蜡螟幼虫的血淋巴中酶(酚氧化酶(PO)和羧酸酯酶(CarE))活性和能源(蛋白质、总糖)含量及其肠道内Imd信号通路中PGRP-LB基因表达量的变化。结果表明:嗜线虫肠杆菌侵入大蜡螟幼虫后,在0~84 h期间,PO和CarE活性表现出“升高—峰值—下降”的变化,血淋巴蛋白质含量持续升高且显著高于对照,总糖含量快速降低且显著低于对照;在0~60 h期间,Imd信号通路中负调控因子PGRP-LB基因表达量呈现急速上升(18 h时表达量最高)又急速下降趋势,而且在适当时间停喂嗜线虫肠杆菌,其肠道内PGRP-LB基因的含量能恢复正常,显示Imd信号通路的免疫调节作用。嗜线虫肠杆菌的侵入对大蜡螟幼虫血腔代谢和肠道免疫系统产生影响,说明它在抑制寄主昆虫免疫反应中发挥重要作用。

In order to investigate the pathogenesis of Xenorhabdus nematophilus on galleria mellonella larvae,the activities of enzymes(phenoloxidase(PO)and carboxylesterase(CarE))and the contents of energy sources(proteins and total sugars)in the hemolymph of larvae invaded by Xenorhabdus nematophilus were measured,as well as the changes in the expression of PGRP-LB genes in the Imd signaling pathway in the intestinal tract.The results showed that,after the invasion of galleria mellonella larvae by Xenorhabdus nematophilus,the activities of PO and CarE showed"increase-peak-decrease"from 0 h to 84 h,the protein content of hemolymph increased continuously and was significantly higher than that of the control,and the content of total sugars decreased rapidly and was significantly lower than that of the control.During the period of 0~60h,the expression of PGRP-LB gene,a negative regulator of Imd signaling pathway,showed a trend of rapid increase(the highest expression at 18 h)and rapid decrease,and the content of PGRP-LB gene in the intestinal tract of Xenorhabdus nematophilus was restored to normal after stopping feeding at an appropriate time,which demonstrated the immunomodulatory effect of Imd signaling pathway.The invasion of Xenorhabdus nematophilus affected the hemocoelomic metabolism and intestinal immune system of galleria mellonella larvae,suggesting that it plays an important role in suppressing the immune response of the host insect.