Department of Plant Medicals, Andong National University, Andong 36729, Republic of Korea.
Department of Plant Medicals, Andong National University, Andong 36729, Republic of Korea.
J Invertebr Pathol. 2018 Sep;157:136-146. doi: 10.1016/j.jip.2018.05.009. Epub 2018 May 24.
Immunity negatively influences bacterial pathogenicity. Eicosanoids mediate both cellular and humoral immune responses in insects. This study tested a hypothesis that differential bacterial virulence of Xenorhabdus/Photorhabdus is dependent on their inhibitory activity against phospholipase A (PLA) activity. P. temperata subsp. temperata ('Ptt') was more than 40 times more potent than X. hominickii ('Xh'). Although both bacteria suppressed cellular immune responses, Ptt infection suppressed hemocyte nodule formation much more than Xh infection. Their differential immunosuppression appeared to be induced by their secondary metabolites because organic extracts of Ptt-cultured broth exhibited higher inhibitory activities against cellular immune responses than Xn-cultured broth extracts. Humoral immune responses were analyzed by measuring expression levels of 11 antimicrobial peptide (AMP) genes. Among inducible AMPs in hemocytes and fat body, higher number and more kinds of AMPs exhibited lower expression levels in Ptt infection than those in Xh infection. Suppressed immune responses induced by Ptt or Xh infection were significantly rescued by the addition of a catalytic product of PLA, suggesting that PLA was a common inhibitory target. In fact, Ptt infection inhibited PLA activity more strongly than Xh infection. RNA interference of a PLA gene decreased its expression and significantly increased bacterial virulence. Moreover, addition of PLA inhibitor to Xh infection enhanced its virulence, similar to virulence level of Ptt infection. These results suggest that variation in Xenorhabdus/Photorhabdus bacterial virulence can be explained by their differential inhibitory activities against host insect PLA.
免疫会对细菌的致病性产生负面影响。类二十烷酸在昆虫中介导细胞和体液免疫反应。本研究检验了一个假设，即不同的 Xenorhabdus/Photorhabdus 细菌的毒力取决于它们对磷脂酶 A (PLA) 活性的抑制活性。P. temperata subsp. temperata（“Ptt”）比 X. hominickii（“Xh”）强 40 多倍。尽管两种细菌都抑制了细胞免疫反应，但 Ptt 感染比 Xh 感染更能抑制血细胞结节的形成。它们的免疫抑制作用似乎是由它们的次生代谢物引起的，因为 Ptt 培养肉汤的有机提取物比 Xn 培养肉汤提取物对细胞免疫反应具有更高的抑制活性。通过测量 11 种抗菌肽 (AMP) 基因的表达水平来分析体液免疫反应。在血细胞和脂肪体中的诱导型 AMP 中，Ptt 感染引起的 AMP 数量更多、种类更多，其表达水平低于 Xh 感染。Ptt 或 Xh 感染诱导的免疫抑制反应通过添加 PLA 的催化产物得到显著挽救，表明 PLA 是共同的抑制靶标。事实上，Ptt 感染比 Xh 感染更强烈地抑制 PLA 活性。PLA 基因的 RNA 干扰降低了其表达水平，并显著增加了细菌的毒力。此外，向 Xh 感染中添加 PLA 抑制剂增强了其毒力，类似于 Ptt 感染的毒力水平。这些结果表明，Xenorhabdus/Photorhabdus 细菌毒力的变化可以用它们对宿主昆虫 PLA 的不同抑制活性来解释。
