Centre for Cell Biology, Development and Disease, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
Instituto de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Avenida Carlos Chagas Filho, 373, Bloco D. Prédio do CCS, Ilha do Fundão, Rio de Janeiro, 21941-902, Brazil.
Parasit Vectors. 2022 Jul 29;15(1):269. doi: 10.1186/s13071-022-05358-9.
Rhodnius prolixus is an important vector of Trypanosoma cruzi, the causal agent of Chagas disease in humans. Despite the medical importance of this and other triatomine vectors, the study of their immune responses has been limited to a few molecular pathways and processes. Insect immunity studies were first described for holometabolous insects such as Drosophila melanogaster, and it was assumed that their immune responses were conserved in all insects. However, study of the immune responses of triatomines and other hemimetabolous insects has revealed discrepancies between these and the Drosophila model.
To expand our understanding of innate immune responses of triatomines to pathogens, we injected fifth instar nymphs of R. prolixus with the Gram-negative (Gr-) bacterium Enterobacter cloacae, the Gram-positive (Gr+) bacterium Staphylococcus aureus, or phosphate-buffered saline (PBS), and evaluated transcript expression in the fat body 8 and 24 h post-injection (hpi). We analyzed the differential expression of transcripts at each time point, and across time, for each treatment.
At 8 hpi, the Gr- bacteria-injected group had a large number of differentially expressed (DE) transcripts, and most of the changes in transcript expression were maintained at 24 hpi. In the Gr+ bacteria treatment, few DE transcripts were detected at 8 hpi, but a large number of transcripts were DE at 24 hpi. Unexpectedly, the PBS control also had a large number of DE transcripts at 24 hpi. Very few DE transcripts were common to the different treatments and time points, indicating a high specificity of the immune responses of R. prolixus to different pathogens. Antimicrobial peptides known to be induced by the immune deficiency pathway were induced upon Gr- bacterial infection. Many transcripts of genes from the Toll pathway that are thought to participate in responses to Gr+ bacteria and fungi were induced by both bacteria and PBS treatment. Pathogen recognition receptors and serine protease cascade transcripts were also overexpressed after Gr- bacteria and PBS injections. Gr- injection also upregulated transcripts involved in the metabolism of tyrosine, a major substrate involved in the melanotic encapsulation response to pathogens.
These results reveal time-dependent pathogen-specific regulation of immune responses in triatomines, and hint at strong interactions between the immune deficiency and Toll pathways.
长红猎蝽是克氏锥虫的重要载体，克氏锥虫是人类恰加斯病的病原体。尽管这种和其他三锥虫媒介具有重要的医学意义，但对它们免疫反应的研究仅限于少数几个分子途径和过程。昆虫免疫研究最初是在完全变态的昆虫如黑腹果蝇中描述的，人们假设它们的免疫反应在所有昆虫中都是保守的。然而，对三锥虫和其他半变态昆虫免疫反应的研究表明，这些昆虫与果蝇模型之间存在差异。
为了扩大我们对三锥虫对病原体先天免疫反应的理解，我们向第五龄若虫注射革兰氏阴性（Gr-）细菌肠杆菌属 cloacae、革兰氏阳性（Gr+）细菌金黄色葡萄球菌或磷酸盐缓冲盐水（PBS），并在注射后 8 和 24 小时评估脂肪体中的转录物表达。我们分析了每个处理在每个时间点的转录物的差异表达，以及跨时间的差异表达。
在 8 hpi 时，Gr-细菌处理组有大量差异表达（DE）的转录物，并且大多数转录物表达的变化在 24 hpi 时仍保持。在 Gr+细菌处理中，在 8 hpi 时检测到的 DE 转录物很少，但在 24 hpi 时有大量的转录物是 DE。出乎意料的是，PBS 对照在 24 hpi 时也有大量的 DE 转录物。不同处理和时间点共同存在的 DE 转录物很少，表明长红猎蝽对不同病原体的免疫反应具有高度特异性。已知由免疫缺陷途径诱导的抗菌肽在 Gr-细菌感染时被诱导。许多被认为参与 Gr+细菌和真菌反应的 Toll 途径的基因转录物被两种细菌和 PBS 处理诱导。病原体识别受体和丝氨酸蛋白酶级联转录物在 Gr-细菌和 PBS 注射后也过表达。Gr-注射还上调了参与酪氨酸代谢的转录物，酪氨酸是一种主要参与对病原体黑化包囊反应的底物。
这些结果揭示了三锥虫中依赖时间的病原体特异性免疫反应的调节，并暗示了免疫缺陷和 Toll 途径之间的强烈相互作用。
