A fat body transcriptome analysis of the immune responses of Rhodnius prolixus to artificial infections with bacteria

Abstract

Background 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. Methods 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. Results 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. Conclusions 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. Graphical abstract

Activation of immune pathways in common bed bugs, Cimex lectularius, in response to bacterial immune challenges - a transcriptomics analysis

“…In this study, defensins and prolixicins were among the most highly up-regulated genes in the midgut, with defensins reaching a log2 fold expression level change of 9. Notably, this level surpasses that reported in comparable studies with kissing bugs, mosquitoes, and vinegar flies, where defensins did not appear to be as highly up-regulated ( 5 , 6 , 9 , 70 , 79 – 85 ). These different levels of expression warrant further exploration.…”

“…They orchestrate cell fate, recycle cellular components, silence foreign nucleic acids, facilitate immune signaling, adapt to environmental challenges, and serve innate immunity roles, thereby ensuring that insects effectively manage infections and maintain resilience against pathogens. The specific genes underlying these immune responses in bed bugs remain unexplored ( 5 , 22 , 33 , 35 , 44 , 86 , 87 , 89 ). We investigated gene regulatory patterns associated with apoptosis and the cysteinyl aspartate protease (CASP) gene families, as well as cellular processes including autophagy, RNAi pathways, serine proteinases, stress responses, and TEPs in both the midgut and RoB following ingestion of bacteria (refer to Supplementary Table S4 ).…”

Arthropod microbiota: shaping pathogen establishment and enabling control

“…Similarly, silencing of the Dorsal gene, the transcription factor of the Toll pathway, also does not alter T. cruzi infection (Figure 1F) (Mesquita et al, 2015). Years later, Salcedo-Porras et al ( 2019) identified additional components of the R. prolixus IMD pathway using reciprocal BLAST and HMM profile searches (Salcedo-Porras et al, 2019).…”

Immune Reactions of Vector Insects to Parasites and Pathogens

“…The insect effector immune factors include antibacterial peptides (AMPs), lectins, prophenoloxidases (PPOs, for melanisation), reactive oxygen species (ROS), nitric oxide (NO), antiviral factors, cytokines and many more [ 17 , 68 , 69 ]. Much of the knowledge of these processes was gleaned by work on Drosophila [ 70 , 71 , 72 ] while valuable contributions have also been made with other species including Aedes/Anopheles mosquitoes [ 18 , 29 , 73 , 74 , 75 ], Hyalophia cecropia [ 76 ], Manduca [ 77 , 78 ], Galleria [ 79 , 80 , 81 ] and Bombyx [ 82 , 83 ] moths, Sarcophaga fleshflies [ 84 , 85 ] and Rhodnius assassin bugs [ 86 , 87 ].…”