Rhodnius prolixus is an insect vector of two flagellate parasites, Trypanosoma rangeli and Trypanosoma cruzi, the latter being the causative agent of Chagas disease in Latin America. The R. prolixus neuroendocrine system regulates the synthesis of the steroid hormone ecdysone, which is essential for not only development and molting but also insect immunity. Knowledge for how this modulates R. prolixus midgut immune responses is essential for understanding interactions between the vector, its parasites and symbiotic microbes. In the present work, we evaluated the effects of ecdysone inhibition on R. prolixus humoral immunity and homeostasis with its microbiota, using the triterpenoid natural product, azadirachtin. Our results demonstrated that azadirachtin promoted a fast and lasting inhibitory effect on expression of both RpRelish, a nuclear factor kappa B transcription factor (NF-kB) component of the IMD pathway, and several antimicrobial peptide (AMP) genes. On the other hand, RpDorsal, encoding the equivalent NF-kB transcription factor in the Toll pathway, and the defC AMP gene were upregulated later in azadirachtin treated insects. The treatment also impacted on proliferation of Serratia marcescens, an abundant commensal bacterium. The simultaneous administration of ecdysone and azadirachtin in R. prolixus blood meals counteracted the azadirachtin effects on insect molting and also on expression of RpRelish and AMPs genes. These results support the direct involvement of ecdysone in regulation of the IMD pathway in the Rhodnius prolixus gut.

Rhodnius prolixus是两种鞭毛虫的昆虫载体，即兰氏锥虫和克氏锥虫，后者是拉丁美洲南美锥虫病的病原体。R. prolixus神经内分泌系统调节类固醇激素蜕皮激素的合成，这不仅对发育和蜕皮而且对昆虫免疫至关重要。了解这如何调节R. prolixus中肠免疫反应对于理解载体、其寄生虫和共生微生物之间的相互作用至关重要。在目前的工作中，我们评估了蜕皮激素抑制对R. prolixus的影响体液免疫和体内平衡及其微生物群，使用三萜类天然产物印楝素。我们的研究结果表明，印楝子素促进了对RpRelish（IMD 通路的一种核因子 kappa B 转录因子 (NF-kB) 组分）和几种抗菌肽 (AMP) 基因的表达的快速和持久的抑制作用。另一方面，RpDorsal，在 Toll 通路中编码等效的 NF-kB 转录因子，而defC AMP 基因后来在印苦楝子素处理的昆虫中上调。该处理还影响粘质沙雷氏菌的增殖，这是一种丰富的共生细菌。R. prolixus中同时施用蜕皮激素和印苦楝子素血粉抵消了印苦楝子素对昆虫蜕皮以及对RpRelish和 AMPs 基因表达的影响。这些结果支持蜕皮激素直接参与调节长红花肠中的 IMD通路。