The IMD and Toll canonical immune pathways of Triatoma pallidipennis are preferentially activated by Gram-negative and Gram-positive bacteria, respectively, but cross-activation also occurs

Abstract

Background Antimicrobial peptides (AMPs) participate in the humoral immune response of insects eliminating invasive microorganisms. The immune deficiency pathway (IMD) and Toll are the main pathways by which the synthesis of these molecules is regulated in response to Gram-negative (IMD pathway) or Gram-positive (Toll pathway) bacteria. Various pattern-recognition receptors (PRRs) participate in the recognition of microorganisms, such as pgrp-lc and toll, which trigger signaling cascades and activate NF-κB family transcription factors, such as relish, that translocate to the cell nucleus, mainly in the fat body, inducing AMP gene transcription. Methods T. pallidipennis inhibited in Tppgrp-lc, Tptoll, and Tprelish were challenged with E. coli and M. luteus to analyze the expression of AMPs transcripts in the fat body and to execute survival assays. Results In this work we investigated the participation of the pgrp-lc and toll receptor genes and the relish transcription factor (designated as Tppgrp-lc, Tptoll, and Tprelish), in the transcriptional regulation of defensin B, prolixicin, and lysozyme B in Triatoma pallidipennis, one of the main vectors of Chagas disease. AMP transcript abundance was higher in the fat body of blood-fed than non-fed bugs. Challenge with Escherichia coli or Micrococcus luteus induced differential increases in AMP transcripts. Additionally, silencing of Tppgrp-lc, Tptoll, and Tprelish resulted in reduced AMP transcription and survival of bugs after a bacterial challenge. Conclusions Our findings demonstrated that the IMD and Toll pathways in T. pallidipennis preferentially respond to Gram-negative and Gram-positive bacteria, respectively, by increasing the expression of AMP transcripts, but cross-induction also occurs. Graphical Abstract

Gcm alleviates the inflammatory phenotype induced by Toll activation inDrosophilahemocytes

“…The induction of the core elements of the Jak/Stat pathway ( Supplementary Figure S2D ) is concordant with ChIP data targeting Dorsal (Dl), which indicates that Dl binds the promoters of all Jak/Stat core components (30). The response to Gram-negative bacteria is commonly associated with the activation of the IMD pathway and illustrates the cross-talk between the Toll and the IMD pathways (31-34). Most core components of the IMD pathways as well as the majority of anti-microbial peptides are upregulated in gcm 26 /+;Toll 10b /+ compared to gcm 26 /+ ( Figure 2A’-A’’’ , B ), suggesting that the Toll pathway may activate the IMD pathway.…”

CircRNAs and their regulatory networks associated with the antioxidant enzymes and immune responses of Asian honey bee larvae to fungal infection

“…These target DEmRNAs were involved in six cellular immune pathways, such as apoptosis, melanogenesis, endocytosis, autophagy-animal, apoptosis -fly, and insect hormone biosynthesis (Figure 8A). Toll, IMD, and JAK/STAT are three vital signaling pathways, among which, the Toll signaling pathway mainly responds to Gram-positive and fungal infestations, while the IMD signaling pathway mainly responds to Gram-negative infestations [76]. The JAK/STAT signaling pathway is mainly involved in antiviral natural immunity and melanism [77].…”

Immune Reactions of Vector Insects to Parasites and Pathogens

“…Most research on triatomines has been carried out on R. prolixus and considerable progress in understanding the complex interaction of T. cruzi with the insect vector is being made [ 4 , 24 , 135 , 136 , 137 , 138 , 139 ]. Phagocytosis by the haemocytes in Rhodnius has been described following T. rangeli invasion from the gut into the haemolymph and following injection of bacteria into the haemolymph [ 140 ].…”

“…36% for E. coli and 41% for Micrococcus luteus after silencing both pathways. This indicated that the Imd and Toll pathways participate jointly to eliminate Gram+ and Gram− bacteria [ 139 ]. Challenging with T. cruzi or T. rangeli and monitoring parasite numbers might have yielded interesting results regarding the participation of the Imd and Toll pathways in immune reactions towards parasites.…”