Isolation and characterization of a novel insect defensin from Rhodnius prolixus, a vector of Chagas disease

Leishmania-sand fly interactions: exploring the role of the immune response and potential strategies for Leishmaniasis control

Leishmaniasis is a neglected tropical disease caused by protozoan parasites of the genus Leishmania, affecting millions of people worldwide. The disease is transmitted by the bite of infected female sand flies, which act as vectors and hosts for the parasites. The interaction between Leishmania parasites and sand flies is complex and dynamic, involving various factors that influence parasite development, survival and transmission. This review examines how the immune response of sand flies affects vector competence and transmission of Leishmania parasites, and what the potential strategies are to prevent or reduce infection. The review also summarizes the main findings and conclusions of the existing literature and discusses implications and recommendations for future research and practice. The study reveals that the immune response of sand flies is a key determinant of vector competence and transmission of Leishmania parasites, and that several molecular and cellular mechanisms are involved in the interaction between parasite and vector. The study also suggests that there are potential strategies for controlling leishmaniasis, such as interfering with parasite development, modulating the vector's immune response or reducing the vector population. However, the study also identifies several gaps and limitations in current knowledge and calls for more comprehensive and systematic studies on vector-parasite interaction and its impact on leishmaniasis transmission and control.

Immune signaling pathways in Rhodnius prolixus in the context of Trypanosoma rangeli infection: cellular and humoral immune responses and microbiota modulation

Introduction

Rhodnius prolixus is a hematophagous insect and one of the main vectors for Trypanosoma cruzi and Trypanosoma rangeli parasites in Latin America. Gut microbiota and insect immune responses affect T. cruzi and T. rangeli infection within triatomines. Particularly the Toll and IMD signaling pathways activations and how they orchestrate the antimicrobial peptides (AMPs) expressions in R. prolixus, especially when infected by T. rangeli.

Objectives

Examine how T. rangeli infection modulates R. prolixus cellular and humoral immunity and its impacts on insect microbiota.

Methods

R. prolixus was fed on blood containing epimastigotes of T. rangeli, and infection was quantified in insect tissues. The gene expression of dorsal, cactus, relish, PGRP, and AMPs was examined in the midgut, fat body, and salivary glands by quantitative real-time PCR. Microbiota composition was analyzed using RT-q PCR targeting specific bacterial species. Hemocyte numbers and phenoloxidase activity were quantified to assess cellular immune responses.

Results

T. rangeli infection modulated triatomine immunity in midgut and hemocoel, activating the expression of the NF-kB gene dorsal, associated with the Toll pathway; increasing expression of the gene encoding PGRP receptor, a component involved in the IMD pathway, both in the intestine and fat body; repressing the expression of the relish transcription factor, mainly in salivary glands. Among the R. prolixus AMPs studied, T. rangeli infection repressed all AMP gene expression, other than defensin C which increased mRNA levels. The PO activity was enhanced in the hemolymph of infected insects. T. rangeli infection did not induce hemocyte number alterations compared to control insects. However, an increase in hemocyte microaggregation was detected in infected insects.

Discussion

R. prolixus recognizes T. rangeli infection and triggers humoral and cellular immune responses involving Toll pathway activation, defensin C synthesis, increased phenoloxidase activity, and enhanced hemocyte aggregation. On the other hand, T. rangeli infection suppressed some IMD pathway components, suggesting that, in R. prolixus, this pathway is involved in defensins A and B gene regulation. Importantly, these immune responses altered the bacterial microbiota composition, potentially favoring T. rangeli establishment in the insect vector.

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

The common bed bug, Cimex lectularius, is an urban pest of global health significance, severely affecting the physical and mental health of humans. In contrast to most other blood-feeding arthropods, bed bugs are not major vectors of pathogens, but the underlying mechanisms for this phenomenon are largely unexplored. Here, we present the first transcriptomics study of bed bugs in response to immune challenges. To study transcriptional variations in bed bugs following ingestion of bacteria, we extracted and processed mRNA from body tissues of adult male bed bugs after ingestion of sterile blood or blood containing the Gram-positive (Gr+) bacterium Bacillus subtilis or the Gram-negative (Gr-) bacterium Escherichia coli. We analyzed mRNA from the bed bugs' midgut (the primary tissue involved in blood ingestion) and from the rest of their bodies (RoB; body minus head and midgut tissues). We show that the midgut exhibits a stronger immune response to ingestion of bacteria than the RoB, as indicated by the expression of genes encoding antimicrobial peptides (AMPs). Both the Toll and Imd signaling pathways, associated with immune responses, were highly activated by the ingestion of bacteria. Bacterial infection in bed bugs further provides evidence for metabolic reconfiguration and resource allocation in the bed bugs' midgut and RoB to promote production of AMPs. Our data suggest that infection with particular pathogens in bed bugs may be associated with altered metabolic pathways within the midgut and RoB that favors immune responses. We further show that multiple established cellular immune responses are preserved and are activated by the presence of specific pathogens. Our study provides a greater understanding of nuances in the immune responses of bed bugs towards pathogens that ultimately might contribute to novel bed bug control tactics.

Resisting an invasion: A review of the triatomine vector (Kissing bug) defense strategies against a Trypanosoma sp infection

Triatomines are an important group of insects in the Americas. They serve as transmission vectors for Trypanosoma cruzi, the etiologic agent responsible for the deadly Chagas disease in humans. The digenetic parasite has a complex life cycle, alternating between mammalian and insect hosts, facing different environments. In the insect vector, the metacyclic trypomastigote (non-replicative) and epimastigote (replicative) stages face a set of insect-mediated environmental changes, such as intestinal pH, body temperature, nutrient availability, and vector immune response. These insects have the ability to differentiate between self and non-self-particles using their innate immune system. This immune system comprises physical barriers, cellular responses (phagocytosis, nodules and encapsulation), humoral factors, including effector mechanisms (antimicrobial peptides and prophenoloxidase cascade) and the intestinal microbiota. Here, we consolidate and synthesize the available literature to describe the defense mechanisms deployed by the triatomine vector against the parasite, as documented in recent years, the possible mechanisms developed by the parasite to protect against the insect's specific microenvironment and innate immune responses, and future perspectives on the Triatomine-Trypanosome interaction.

Characterization of New Defensin Antimicrobial Peptides and Their Expression in Bed Bugs in Response to Bacterial Ingestion and Injection

Common bed bugs, Cimex lectularius, can carry, but do not transmit, pathogens to the vertebrate hosts on which they feed. Some components of the innate immune system of bed bugs, such as antimicrobial peptides (AMPs), eliminate the pathogens. Here, we determined the molecular characteristics, structural properties, and phylogenetic relatedness of two new defensins (CL-defensin1 (XP_024085718.1), CL-defensin2 (XP_014240919.1)), and two new defensin isoforms (CL-defensin3a (XP_014240918.1), CL-defensin3b (XP_024083729.1)). The complete amino acid sequences of CL-defensin1, CL-defensin2, CL-defensin3a, and CL-defensin3b are strongly conserved, with only minor differences in their signal and pro-peptide regions. We used a combination of comparative transcriptomics and real-time quantitative PCR to evaluate the expression of these defensins in the midguts and the rest of the body of insects that had been injected with bacteria or had ingested blood containing the Gram-positive (Gr+) bacterium Bacillus subtilis and the Gram-negative (Gr–) bacterium Escherichia coli. We demonstrate, for the first time, sex-specific and immunization mode-specific upregulation of bed bug defensins in response to injection or ingestion of Gr+ or Gr– bacteria. Understanding the components, such as these defensins, of the bed bugs’ innate immune systems in response to pathogens may help unravel why bed bugs do not transmit pathogens to vertebrates.

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

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.

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

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.

Rhodnius prolixus Hemolymph Immuno-Physiology: Deciphering the Systemic Immune Response Triggered by Trypanosoma cruzi Establishment in the Vector Using Quantitative Proteomics

Understanding the development of Trypanosoma cruzi within the triatomine vector at the molecular level should provide novel targets for interrupting parasitic life cycle and affect vectorial competence. The aim of the current study is to provide new insights into triatomines immunology through the characterization of the hemolymph proteome of Rhodnius prolixus, a major Chagas disease vector, in order to gain an overview of its immune physiology. Surprisingly, proteomics investigation of the immunomodulation of T. cruzi-infected blood reveals that the parasite triggers an early systemic response in the hemolymph. The analysis of the expression profiles of hemolymph proteins from 6 h to 24 h allowed the identification of a broad range of immune proteins expressed already in the early hours post-blood-feeding regardless of the presence of the parasite, ready to mount a rapid response exemplified by the significant phenol oxidase activation. Nevertheless, we have also observed a remarkable induction of the immune response triggered by an rpPGRP-LC and the overexpression of defensins 6 h post-T. cruzi infection. Moreover, we have identified novel proteins with immune properties such as the putative c1q-like protein and the immunoglobulin I-set domain-containing protein, which have never been described in triatomines and could play a role in T. cruzi recognition. Twelve proteins with unknown function are modulated by the presence of T. cruzi in the hemolymph. Determining the function of these parasite-induced proteins represents an exciting challenge for increasing our knowledge about the diversity of the immune response from the universal one studied in holometabolous insects. This will provide us with clear answers for misunderstood mechanisms in host-parasite interaction, leading to the development of new generation strategies to control vector populations and pathogen transmission.

Salivary and Intestinal Transcriptomes Reveal Differential Gene Expression in Starving, Fed and Trypanosoma cruzi-Infected Rhodnius neglectus

Rhodnius neglectus is a potential vector of Trypanosoma cruzi (Tc), the causative agent of Chagas disease. The salivary glands (SGs) and intestine (INT) are actively required during blood feeding. The saliva from SGs is injected into the vertebrate host, modulating immune responses and favoring feeding for INT digestion. Tc infection significantly alters the physiology of these tissues; however, studies that assess this are still scarce. This study aimed to gain a better understanding of the global transcriptional expression of genes in SGs and INT during fasting (FA), fed (FE), and fed in the presence of Tc (FE + Tc) conditions. In FA, the expression of transcripts related to homeostasis maintenance proteins during periods of stress was predominant. Therefore, the transcript levels of Tret1-like and Hsp70Ba proteins were increased. Blood appeared to be responsible for alterations found in the FE group, as most of the expressed transcripts, such as proteases and cathepsin D, were related to digestion. In FE + Tc group, there was a decreased expression of blood processing genes for insect metabolism (e.g., Antigen-5 precursor, Pr13a, and Obp), detoxification (Sult1) in INT and acid phosphatases in SG. We also found decreased transcriptional expression of lipocalins and nitrophorins in SG and two new proteins, pacifastin and diptericin, in INT. Several transcripts of unknown proteins with investigative potential were found in both tissues. Our results also show that the presence of Tc can change the expression in both tissues for a long or short period of time. While SG homeostasis seems to be re-established on day 9, changes in INT are still evident. The findings of this study may be used for future research on parasite-vector interactions and contribute to the understanding of food physiology and post-meal/infection in triatomines.

Structural and functional characterizations and heterogenous expression of the antimicrobial peptides, Hidefensins, from black soldier fly, Hermetia illucens (L.)

Insect defensins are effector components of the innate defense system. Defensins, which are widely distributed among insects, are a type of small cysteine-rich plant antimicrobial peptides with broad-spectrum antimicrobial activity. Here, the cDNAs of the black soldier fly, Hermetia illucens (L.), encoding six defensins, designated herein as Hidefensin1-1, 2, 3, 4, 5, 6. Moreover, Hidefensin1-1, 2, and 5 were identified for the first time by genome-targeted analysis. These Hidefensins were found to mainly adopt α-helix and β-sheet conformation homology as modeled by PRABI, Swiss-Model and ProFunc server. Six conserved cysteine residues that contribute to three disulfide bonds formed the spacing pattern "C-X₁₂-C-X₃-C-X₉-C-X₅-C-X-C", which play a vital role in the molecular stability of Hidefensins. Phylogenetic analysis revealed that the homology of five Hidefensins (except Hidefensin4) was about 59%-92% compared with other insect defensins, indicating that they are novel antimicrobial peptides genes in black soldier fly. Furthermore, the Hidefensin1-1 was expressed in the Escherichia coli strain BL21(DE3) as a fusion protein with thioredoxin. Results showed that the purified TRX-Hidefensin1-1 exerted strong inhibitory effects against the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli. The inhibitory efficacy of TRX-Hidefensin1-1 against Gram-positive bacteria was better than that against Gram-negative bacteria. These results indicated that Hidefensin1-1 has potent antimicrobial activities against test pathogens.

Differential activity on trypanosomatid parasites of a novel recombinant defensin type 1 from the insect Triatoma (Meccus) pallidipennis

Defensins are one of the major families of antimicrobial peptides (AMPs) that are widely distributed in insects. In Triatomines (Hemiptera: Reduviidae) vectors of Trypanosoma cruzi the causative agent of Chagas disease, two large groups of defensin isoforms have been described: type 1 and type 4. The aim of this study was to analyze the trypanocidal activity of a type 1 recombinant defensin (rDef1.3) identified in Triatoma (Meccus) pallidipennis, an endemic specie from México. The trypanocidal activity of this defensin was evaluated in vitro, against the parasites T. cruzi, T. rangeli, and two species of Leishmania (L. mexicana and L. major) both causative agents of cutaneous leishmaniasis. Our data demonstrated that the defensin was active against all the parasites although in different degrees. The defensin altered the morphology, reduced the viability and inhibited the growth of T.cruzi. When tested against T. rangeli (a parasite that infects a variety of mammalian species), stronger morphological effects where observed. Surprisingly the greatest effects were observed against the two Leishmania species, of which L. major was the parasite most affected with 50% of dead cells or with damaged membranes, in addition of a reduction in its proliferative capacity in culture. These results suggest that rDef1.3 has an important antimicrobial effect against trypanosomatids which cause some of the more important neglected tropical diseases transmitted by insect vectors.

Time- and tissue-specific antimicrobial activity of the common bed bug in response to blood feeding and immune activation by bacterial injection

Unlike almost all hematophagous insects, common bed bugs, Cimex lectularius, are not known to transmit pathogens to humans. To help unravel the reasons for their lack of vector competence, we studied the time- and tissue-dependent expression of innate immune factors after blood feeding or immune activation through the intrathoracic injection of bacteria. We used minimum inhibitory concentration (MIC¹) bioassays and the Kirby-Bauer protocol to evaluate antimicrobial peptide (AMP²) activity in tissue extracts from the midguts or 'rest of body' (RoB³) tissues (containing hemolymph and fat body AMPs) against Gram-positive and Gram-negative bacteria. We compared AMP activity between blood-fed female bed bugs and yellow fever mosquitoes, Aedes aegypti and determined how female and male bed bugs respond to immune challenges, and how long AMP gene expression remains elevated in bed bugs following a blood meal. Blood meal-induced AMP activity is 4-fold stronger in female bed bugs than in female mosquitoes. Male bed bugs have elevated AMP activity within 8 h of a blood meal or an intrathoracic injection with bacteria, with the strongest activity expressed in RoB tissue 24 h after the immune challenge. Female bed bugs have a stronger immune response than males within 24 h of a blood meal. The effects of blood meal-induced elevated AMP activity lasts longer against the Gram-positive bacterium, Bacillus subtilis, than against the Gram-negative bacterium Escherichia coli. Unravelling the specific immune pathways that are activated in the bed bugs' immune responses and identifying the bed bug-unique AMPs might help determine why these insects are not vectors of human parasites.

Modulation of IMD, Toll, and Jak/STAT Immune Pathways Genes in the Fat Body of Rhodnius prolixus During Trypanosoma rangeli Infection

Trypanosoma rangeli is the second most common American trypanosome that infects man. It is vectored by triatomines from the genus Rhodnius, in which it invades the hemolymph and infects the salivary glands, avoiding the bug immune responses. In insects, these responses are initiated by well conserved pathways, mainly the IMD, Toll, and Jak/STAT. We hypothesize that long-term infection with T. rangeli in the gut or hemolymph of Rhodnius prolixus triggers different systemic immune responses, which influence the number of parasites that survive inside the vector. Thus, we investigated groups of insects with infections in the gut and/or hemolymph, and evaluated the parasite load and the expression in the fat body of transcription factors (Rp-Relish, Rp-Dorsal, and Rp-STAT) and inhibitors (Rp-Cactus and Rp-Caspar) of the IMD, Toll, and Jak/STAT pathways. We detected lower parasite counts in the gut of insects without hemolymph infection, compared to hemolymph-infected groups. Besides, we measured higher parasite numbers in the gut of bugs that were first inoculated with T. rangeli and then fed on infected mice, compared with control insects, indicating that hemolymph infection increases parasite numbers in the gut. Interestingly, we observed that genes from the three immune pathways where differentially modulated, depending on the region parasites were present, as we found (1) Rp-Relish downregulated in gut-and/or-hemolymph-infected insects, compared with controls; (2) Rp-Cactus upregulated in gut-infected insect, compared with controls and gut-and-hemolymph-infected groups; and (3) Rp-STAT downregulated in all groups of hemolymph-infected insects. Finally, we uncovered negative correlations between parasite loads in the gut and Rp-Relish and Rp-Cactus expression, and between parasite counts in the hemolymph and Rp-Relish levels, suggesting an association between parasite numbers and the IMD and Toll pathways. Overall, our findings reveal new players in R. prolixus-T. rangeli interactions that could be key for the capacity of the bug to transmit the pathogen.

A rhamnose-binding lectin from Rhodnius prolixus and the impact of its silencing on gut bacterial microbiota and Trypanosoma cruzi

Lectins are ubiquitous proteins involved in the immune defenses of different organisms and mainly responsible for non-self-recognition and agglutination reactions. This work describes molecular and biological characterization of a rhamnose-binding lectin (RBL) from Rhodnius prolixus, which possesses a 21 amino acid signal peptide and a mature protein of 34.6 kDa. The in-silico analysis of the primary and secondary structures of RpLec revealed a lectin domain fully conserved among previous insects studied. The three-dimensional homology model of RpLec was similar to other RBL-lectins. Docking predictions with the monosaccharides showed rhamnose and galactose-binding sites comparable to Latrophilin-1 and N-Acetylgalactosamine-binding in a different site. The effects of RpLec gene silencing on levels of infecting Trypanosoma cruzi Dm 28c and intestinal bacterial populations in the R. prolixus midgut were studied by injecting RpLec dsRNA into the R. prolixus hemocoel. Whereas T. cruzi numbers remained unchanged compared with the controls, numbers of bacteria increased significantly. The silencing also induced the up regulation of the R. prolixus defC (defensin) expression gene. These results with RpLec reveal the potential importance of this little studied molecule in the insect vector immune response and homeostasis of the gut bacterial microbiota.

Rhodnius prolixus uses the peptidoglycan recognition receptor rpPGRP-LC/LA to detect Gram-negative bacteria and activate the IMD pathway

Insects rely on an innate immune system to recognize and eliminate pathogens. Key components of this system are highly conserved across all invertebrates. To detect pathogens, insects use Pattern recognition receptors (PRRs) that bind to signature motifs on the surface of pathogens called Pathogen Associated Molecular Patterns (PAMPs). In general, insects use peptidoglycan recognition proteins (PGRPs) in the Immune Deficiency (IMD) pathway to detect Gram-negative bacteria, and other PGRPs and Gram-negative binding proteins (GNBPs) in the Toll pathway to detect Gram-positive bacteria and fungi, although there is crosstalk and cooperation between these and other pathways. Once pathogens are recognized, these pathways activate the production of potent antimicrobial peptides (AMPs). Most PRRs in insects have been reported from genome sequencing initiatives but few have been characterized functionally. The initial studies on insect PRRs were done using established dipteran model organisms such as Drosophila melanogaster, but there are differences in the numbers and functional role of PRRs in different insects. Here we describe the genomic repertoire of PGRPs in Rhodnius prolixus, a hemimetabolous hemipteran vector of the parasite Trypanosoma cruzi that causes Chagas disease in humans. Using a de novo transcriptome from the fat body of immune activated insects, we found 5 genes encoding PGRPs. Phylogenetic analysis groups R. prolixus PGRPs with D. melanogaster PGRP-LA, which is involved in the IMD pathway in the respiratory tract. A single R. prolixus PGRP gene encodes isoforms that contain an intracellular region or motif (cryptic RIP Homotypic Interaction Motif-cRHIM) that is involved in the IMD signaling pathway in D. melanogaster. We characterized and silenced this gene using RNAi and show that the PGRPs that contain cRHIMs are involved in the recognition of Gram-negative bacteria, and activation of the IMD pathway in the fat body of R. prolixus, similar to the PGRP-LC of D. melanogaster. This is the first functional characterization of a PGRP containing a cRHIM motif that serves to activate the IMD pathway in a hemimetabolous insect.

Azadirachtin interferes with basal immunity and microbial homeostasis in the Rhodnius prolixus midgut

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.

Proteome of the Triatomine Digestive Tract: From Catalytic to Immune Pathways; Focusing on Annexin Expression

Rhodnius prolixus, Panstrongylus megistus, Triatoma infestans, and Dipetalogaster maxima are all triatomines and potential vectors of the protozoan Trypanosoma cruzi responsible for human Chagas' disease. Considering that the T. cruzi's cycle occurs inside the triatomine digestive tract (TDT), the analysis of the TDT protein profile is an essential step to understand TDT physiology during T. cruzi infection. To characterize the protein profile of TDT of D. maxima, P. megistus, R. prolixus, and T. infestans, a shotgun liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach was applied in this report. Most proteins were found to be closely related to metabolic pathways such as gluconeogenesis/glycolysis, citrate cycle, fatty acid metabolism, oxidative phosphorylation, but also to the immune system. We annotated this new proteome contribution gathering it with those previously published in accordance with Gene Ontology and KEGG. Enzymes were classified in terms of class, acceptor, and function, while the proteins from the immune system were annotated by reference to the pathways of humoral response, cell cycle regulation, Toll, IMD, JNK, Jak-STAT, and MAPK, as available from the Insect Innate Immunity Database (IIID). These pathways were further subclassified in recognition, signaling, response, coagulation, melanization and none. Finally, phylogenetic affinities and gene expression of annexins were investigated for understanding their role in the protection and homeostasis of intestinal epithelial cells against the inflammation.

The innate immune system of kissing bugs, vectors of chagas disease

Kissing bugs have long served as models to study many aspects of insect physiology. They also serve as vectors for the parasite Trypanosoma cruzi that causes Chagas disease in humans. The overall success of insects is due, in part, to their ability to recognize parasites and pathogens as non-self and to eliminate them using their innate immune system. This immune system comprises physical barriers, cellular responses (phagocytosis, nodulation and encapsulation), and humoral factors (antimicrobial peptides and the prophenoloxidase cascade). Trypanosoma cruzi survives solely in the gastrointestinal (GI) tract of the vector; if it migrates to the hemocoel it is eliminated. Kissing bugs may not mount a vigorous immune response in the GI tract to avoid eliminating obligate symbiotic microbes on which they rely for survival. Here we describe the current knowledge of innate immunity in kissing bugs and new opportunities using genomic and transcriptomic approaches to study the complex triatomine-trypanosome-microbiome interactions.

The limpet transcription factors of Triatoma infestans regulate the response to fungal infection and modulate the expression pattern of defensin genes

As part of the innate humoral response to microbial attack, insects activate the expression of antimicrobial peptides (AMP). Understanding the regulatory mechanisms of this response in the Chagas disease vector Triatoma infestans is important since biological control strategies against pyrethroid-resistant insect populations were recently addressed by using the entomopathogenic fungus Beauveria bassiana. By bioinformatics, gene expression, and silencing techniques in T. infestans nymphs, we achieved sequence and functional characterization of two variants of the limpet transcription factor (Tilimpet) and studied their role as regulators of the AMP expression, particularly defensins, in fungus-infected insects. We found that Tilimpet variants may act differentially since they have divergent sequences and different relative expression ratios, suggesting that Tilimpet-2 could be the main regulator of the higher expressed defensins and Tilimpet-1 might play a complementary or more general role. Also, the six defensins (Tidef-1 to Tidef-6) exhibited different expression levels in fungus-infected nymphs, consistent with their phylogenetic clustering. This study aims to contribute to a better understanding of T. infestans immune response in which limpet is involved, after challenge by B. bassiana infection.

Rhodnius prolixus: Identification of missing components of the IMD immune signaling pathway and functional characterization of its role in eliminating bacteria

The innate immune system in insects is regulated by specific signalling pathways. Most immune related pathways were identified and characterized in holometabolous insects such as Drosophila melanogaster, and it was assumed they would be highly conserved in all insects. The hemimetabolous insect, Rhodnius prolixus, has served as a model to study basic insect physiology, but also is a major vector of the human parasite, Trypanosoma cruzi, that causes 10,000 deaths annually. The publication of the R. prolixus genome revealed that one of the main immune pathways, the Immune-deficiency pathway (IMD), was incomplete and probably non-functional, an observation shared with other hemimetabolous insects including the pea aphid (Acyrthosiphon pisum) and the bedbug (Cimex lectularius). It was proposed that the IMD pathway is inactive in R. prolixus as an adaptation to prevent eliminating beneficial symbiont gut bacteria. We used bioinformatic analyses based on reciprocal BLAST and HMM-profile searches to find orthologs for most of the "missing" elements of the IMD pathway and provide data that these are regulated in response to infection with Gram-negative bacteria. We used RNAi strategies to demonstrate the role of the IMD pathway in regulating the expression of specific antimicrobial peptides (AMPs) in the fat body of R. prolixus. The data indicate that the IMD pathway is present and active in R. prolixus, which opens up new avenues of research on R. prolixus-T. cruzi interactions.

Variability of defensin genes from a Mexican endemic Triatominae: Triatoma (Meccus) pallidipennis (Hemiptera: Reduviidae)

Chagas disease remains a serious health problem for countries where the most common mode of transmission is infection contracted from the feces of a Triatominae insect vector. In México, 32 species of Triatoma have been identified; amongst them, Triatoma (Meccus) pallidipennis is an endemic species reported to have high percentages of infection with T. cruzi Defensins, cysteine-rich cationic peptides, are a family of antimicrobial peptides (AMPs); the synthesis of these molecules is crucial for insect's immune defense. In the present study, the genes encoding defensins in T. pallidipennis were sequenced with the purpose of identifying the variability of these genes in a Mexican vector of T. cruzi We found 12 different genes encoding three mature peptides, all of which had the typical folding of a functional insect defensin. In this work two Defensins type 1 and one type 4 were identified. The pro-peptide domain was highly variable and the mature peptide was not. This is the first report focus on variability of defensins from an epidemiologically important Triatoma in Mexico.

The NF-κB Inhibitor, IMD-0354, Affects Immune Gene Expression, Bacterial Microbiota and Trypanosoma cruzi Infection in Rhodnius prolixus Midgut

Rhodnius prolixus is an insect vector of Trypanosoma cruzi, the causative agent of Chagas disease in Latin America. Nuclear factor-κB (NF-κB) transcription factors (TF) are conserved components of the innate immune system in several multicellular organisms including insects. The drug IMD-0354 [N-(3,5-bis-trifluoromethyl-phenyl)-5-chloro-2-hydroxy-benzamide] is a selective inhibitor of IκB kinases. It blocks IκBα phosphorylation thus preventing nuclear translocation of the NF-κb TF. In humans, NF-κB is involved in several biological processes such as inflammation, cell proliferation and immunity. In insects, the activation of the immune system upon microbial challenge can be controlled by signaling pathways such as the immune deficiency (IMD) and Toll, to combat infection. These activated pathways signal to downstream NF-κB TF to stimulate specific immune genes, triggering the synthesis of several molecules such as the antimicrobial peptides. In Drosophila melanogaster, the activation and regulation of NF-κB TF have been elucidated, while in triatomines these mechanisms are not fully understood Therefore, the present study investigated the effects of oral administration of the drug IMD-0354 on the R. prolixus immune response to challenge with bacteria and T. cruzi, as well as the impact on the gut bacterial microbiota. R. prolixus were fed with rabbit blood containing IMD-0354 and Escherichia coli, Staphylococcus aureus, or T. cruzi. The effects of IMD-0354 on insect mortality and antimicrobial activity in insect midgut samples, as well as the relative expression of R. prolixus immune genes were recorded. The bacterial microbiota was analyzed, and viable parasites were counted in insect midgut samples. The IMD-0354 treatment modulated antibacterial activity and the gene expression patterns of defensin A, defensin B, defensin C, and prolixicin, and the genes involved in the IMD and Toll pathways. Additionally, there was an increase of bacterial microbiota in treated insects. Insects treated with IMD-0354 and concomitantly infected with bacteria or T. cruzi through the blood meal had increased mortality, while the T. cruzi population in R. prolixus midgut was reduced. The inhibitory effect of IMD-0354 indicates the importance of NF-κB TF in the innate immune responses involved in the control of bacteria and parasite infections in the R. prolixus midgut.

What makes an effective Chagas disease vector? Factors underlying Trypanosoma cruzi-triatomine interactions

The Chagas disease is caused by the parasite Trypanosoma cruzi, which infect blood-feeding triatomine bugs to finally reach mammal hosts. Chagas disease is endemic in Latin America, and is ranked among the 13 neglected tropical diseases worldwide. Currently, an estimate of 7 million people is infected by T. cruzi, leading to about 22 000 deaths per year throughout the Americas. As occurs with other vectors, a major question towards control programs is what makes a susceptible bug. In this review, we focus on findings linked to insect gut structure and microbiota, immunity, genetics, blood sources, abiotic factors (with special reference to ambient temperature and altitude) to understand the interactions occurring between T. cruzi and triatomine bugs, under a co-evolutionary scenario. These factors lead to varying fitness benefits and costs for bugs, explaining why infection in the insect takes place and how it varies in time and space. Our analysis highlights that major factors are gut components and microbiota, blood sources and temperature. Although their close interaction has never been clarified, knowledge reviewed here may help to boost the success of triatomine control programs, reducing the use of insecticides.

Comparative genomics analysis of triatomines reveals common first line and inducible immunity-related genes and the absence of Imd canonical components among hemimetabolous arthropods

Background

Insects operate complex humoral and cellular immune strategies to fend against invading microorganisms. The majority of these have been characterized in Drosophila and other dipterans. Information on hemipterans, including Triatominae vectors of Chagas disease remains incomplete and fractionated.

Results

We identified putative immune-related homologs of three Triatominae vectors of Chagas disease, Triatoma pallidipennis, T. dimidiata and T. infestans (TTTs), using comparative transcriptomics based on established immune response gene references, in conjunction with the predicted proteomes of Rhodnius prolixus, Cimex lecticularis and Acyrthosiphon pisum hemimetabolous. We present a compressive description of the humoral and cellular innate immune components of these TTTs and extend the immune information of other related hemipterans. Key homologs of the constitutive and induced immunity genes were identified in all the studied hemipterans.

Conclusions

Our results in the TTTs extend previous observations in other hemipterans lacking several components of the Imd signaling pathway. Comparison with other hexapods, using published data, revealed that the absence of various Imd canonical components is common in several hemimetabolous species.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2561-2) contains supplementary material, which is available to authorized users.

The NF-κB Inhibitor, IMD-0354, Affects Immune Gene Expression, Bacterial Microbiota and Trypanosoma cruzi Infection in Rhodnius prolixus Midgut

Rhodnius prolixus is an insect vector of Trypanosoma cruzi, the causative agent of Chagas disease in Latin America. Nuclear factor-κB (NF-κB) transcription factors (TF) are conserved components of the innate immune system in several multicellular organisms including insects. The drug IMD-0354 [N-(3,5-bis-trifluoromethyl-phenyl)-5-chloro-2-hydroxy-benzamide] is a selective inhibitor of IκB kinases. It blocks IκBα phosphorylation thus preventing nuclear translocation of the NF-κb TF. In humans, NF-κB is involved in several biological processes such as inflammation, cell proliferation and immunity. In insects, the activation of the immune system upon microbial challenge can be controlled by signaling pathways such as the immune deficiency (IMD) and Toll, to combat infection. These activated pathways signal to downstream NF-κB TF to stimulate specific immune genes, triggering the synthesis of several molecules such as the antimicrobial peptides. In Drosophila melanogaster, the activation and regulation of NF-κB TF have been elucidated, while in triatomines these mechanisms are not fully understood Therefore, the present study investigated the effects of oral administration of the drug IMD-0354 on the R. prolixus immune response to challenge with bacteria and T. cruzi, as well as the impact on the gut bacterial microbiota. R. prolixus were fed with rabbit blood containing IMD-0354 and Escherichia coli, Staphylococcus aureus, or T. cruzi. The effects of IMD-0354 on insect mortality and antimicrobial activity in insect midgut samples, as well as the relative expression of R. prolixus immune genes were recorded. The bacterial microbiota was analyzed, and viable parasites were counted in insect midgut samples. The IMD-0354 treatment modulated antibacterial activity and the gene expression patterns of defensin A, defensin B, defensin C, and prolixicin, and the genes involved in the IMD and Toll pathways. Additionally, there was an increase of bacterial microbiota in treated insects. Insects treated with IMD-0354 and concomitantly infected with bacteria or T. cruzi through the blood meal had increased mortality, while the T. cruzi population in R. prolixus midgut was reduced. The inhibitory effect of IMD-0354 indicates the importance of NF-κB TF in the innate immune responses involved in the control of bacteria and parasite infections in the R. prolixus midgut.

Campylobacter jejuni in Musca domestica: An examination of survival and transmission potential in light of the innate immune responses of the house flies

The house fly, Musca domestica, has been implicated as a vector of Campylobacter spp., a major cause of human disease. Little is known whether house flies serve as biological amplifying hosts or mechanical vectors for Campylobacter jejuni. We investigated the period after C. jejuni had been ingested by house flies in which viable C. jejuni colonies could be isolated from whole bodies, the vomitus and the excreta of adult M. domestica and evaluated the activation of innate immune responses of house flies to ingested C. jejuni over time. C. jejuni could be cultured from infected houseflies soon after ingestion but no countable C. jejuni colonies were observed > 24 h postingestion. We detected viable C. jejuni in house fly vomitus and excreta up to 4 h after ingestion, but no viable bacteria were detected ≥ 8 h. Suppression subtractive hybridization identified pathogen-induced gene expression in the intestinal tracts of adult house flies 4-24 h after ingesting C. jejuni. We measured the expression of immune regulatory (thor, JNK, and spheroide) and effector (cecropin, diptericin, attacin, defensing, and lysozyme) genes in C. jejuni-infected and -uninfected house flies using quantitative real time PCR. Some house fly factor, or combination of factors, eliminates C. jejuni within 24 h postingestion. Because C. jejuni is not amplified within the body of the housefly, this insect likely serves as a mechanical vector rather than as a true biological, amplifying vector for C. jejuni, and adds to our understanding of insect-pathogen interactions.

Structure-Activity Relationships of Insect Defensins

Insects make up the largest and most diverse group of organisms on earth with several million species to exist in total. Considering the sheer number of insect species and the vast variety of ways they interact with their environment through chemistry, it is clear that they have significant potential as a source of new lead molecules. They have adapted to a range of ecological habitats and exhibit a symbiotic lifestyle with various microbes such as bacteria and fungi. Accordingly, numerous antimicrobial compounds have been identified including for example defensin peptides. Insect defensins were found to have broad-spectrum activity against various gram-positive/negative bacteria as well as fungi. They exhibit a unique structural topology involving the complex arrangement of three disulfide bonds as well as an alpha helix and beta sheets, which is known as cysteine-stabilized αβ motif. Their stability and amenability to peptide engineering make them promising candidates for the development of novel antibiotics lead molecules. This review highlights the current knowledge regarding the structure-activity relationships of insect defensin peptides and provides basis for future studies focusing on the rational design of novel cysteine-rich antimicrobial peptides.

Rhodnius prolixus: from physiology by Wigglesworth to recent studies of immune system modulation by Trypanosoma cruzi and Trypanosoma rangeli

This review is dedicated to the memory of Professor Sir Vincent B. Wigglesworth (VW) in recognition of his many pioneering contributions to insect physiology which, even today, form the basis of modern-day research in this field. Insects not only make vital contributions to our everyday lives by their roles in pollination, balancing eco-systems and provision of honey and silk products, but they are also outstanding models for studying the pathogenicity of microorganisms and the functioning of innate immunity in humans. In this overview, the immune system of the triatomine bug, Rhodnius prolixus, is considered which is most appropriate to this dedication as this insect species was the favourite subject of VW's research. Herein are described recent developments in knowledge of the functioning of the R. prolixus immune system. Thus, the roles of the cellular defences, such as phagocytosis and nodule formation, as well as the role of eicosanoids, ecdysone, antimicrobial peptides, reactive oxygen and nitrogen radicals, and the gut microbiota in the immune response of R. prolixus are described. The details of many of these were unknown to VW although his work gives indications of his awareness of the importance to R. prolixus of cellular immunity, antibacterial activity, prophenoloxidase and the gut microbiota. This description of R. prolixus immunity forms a backdrop to studies on the interaction of the parasitic flagellates, Trypanosoma cruzi and Trypanosoma rangeli, with the host defences of this important insect vector. These parasites remarkably utilize different strategies to avoid/modulate the triatomine immune response in order to survive in the extremely hostile host environments present in the vector gut and haemocoel. Much recent information has also been gleaned on the remarkable diversity of the immune system in the R. prolixus gut and its interaction with trypanosome parasites. This new data is reviewed and gaps in our knowledge of R. prolixus immunity are identified as subjects for future endeavours. Finally, the publication of the T. cruzi, T. rangeli and R. prolixus genomes, together with the use of modern molecular techniques, should lead to the enhanced identification of the determinants of infection derived from both the vector and the parasites which, in turn, could form targets for new molecular-based control strategies.

Antiparasitic peptides

: The most important parasitic diseases, malaria, leishmaniasis, trypanosomiasis, and schistosomiasis, are a great burden to mankind, threatening the life of millions of people worldwide and mostly affecting the poorest. Because drug resistance is increasing and vaccines are rarely available, novel chemotherapeutic compounds are necessary in order to treat these devastating diseases. Insects serve as vectors of many human parasitic diseases and have been shown to express a huge variety of antimicrobial peptides (AMPs). Therefore, research activity on insect-derived AMPs has been increasing in the last 40 years. This chapter summarizes the current state of research on the possible role of AMPs as potential chemotherapeutic compounds against human parasitic diseases. As a representative antimicrobial peptide with antiparasitic activity, the structure of insect defensin A is shown [PDB accession code: 1ICA]. The molecule is surrounded by schematic representations of the human pathogenic parasites Plasmodium, Leishmania and Trypanosoma.

Interactions between Trypanosoma cruzi Secreted Proteins and Host Cell Signaling Pathways

Chagas disease is one of the prevalent neglected tropical diseases, affecting at least 6-7 million individuals in Latin America. It is caused by the protozoan parasite Trypanosoma cruzi, which is transmitted to vertebrate hosts by blood-sucking insects. After infection, the parasite invades and multiplies in the myocardium, leading to acute myocarditis that kills around 5% of untreated individuals. T. cruzi secretes proteins that manipulate multiple host cell signaling pathways to promote host cell invasion. The primary secreted lysosomal peptidase in T. cruzi is cruzipain, which has been shown to modulate the host immune response. Cruzipain hinders macrophage activation during the early stages of infection by interrupting the NF-kB P65 mediated signaling pathway. This allows the parasite to survive and replicate, and may contribute to the spread of infection in acute Chagas disease. Another secreted protein P21, which is expressed in all of the developmental stages of T. cruzi, has been shown to modulate host phagocytosis signaling pathways. The parasite also secretes soluble factors that exert effects on host extracellular matrix, such as proteolytic degradation of collagens. Finally, secreted phospholipase A from T. cruzi contributes to lipid modifications on host cells and concomitantly activates the PKC signaling pathway. Here, we present a brief review of the interaction between secreted proteins from T. cruzi and the host cells, emphasizing the manipulation of host signaling pathways during invasion.

cDNA cloning and molecular characterization of a defensin-like antimicrobial peptide from larvae of Protaetia brevitarsis seulensis (Kolbe)

We identified new defensin-like cDNA (called Psdefensin) by searching data set of high-throughput RNA sequencing (RNA-seq) expression profiling of immunized larva of white-spotted flower chafers, Protaetia brevitarsis seulensis. The length of the analyzed new defensin-like sequences were 240 base pair (bp) and encoded the deduced polypeptide of 79 amino acid residues with signal peptides (amino acids 1-20), pro-peptide region (amino acids 21-36), and mature peptide region (amino acids 37-79). The Psdefensin transcript levels were slightly up-regulated at 4 h post-infection and were highly expressed at 8 h post-infection compared to control larvae injected with sterile water. In addition, the Psdefensin did have antimicrobial activity against both Gram-negative bacteria, E. coli and Gram-positive bacteria, B. subtilis suggesting potentially pharmacologic agent.

Impact of Trypanosoma cruzi on antimicrobial peptide gene expression and activity in the fat body and midgut of Rhodnius prolixus

Background

Rhodnius prolixus is a major vector of Trypanosoma cruzi, the causative agent of Chagas disease in Latin America. In natural habitats, these insects are in contact with a variety of bacteria, fungi, virus and parasites that they acquire from both their environments and the blood of their hosts. Microorganism ingestion may trigger the synthesis of humoral immune factors, including antimicrobial peptides (AMPs). The objective of this study was to compare the expression levels of AMPs (defensins and prolixicin) in the different midgut compartments and the fat body of R. prolixus infected with different T. cruzi strains. The T. cruzi Dm 28c clone (TcI) successfully develops whereas Y strain (TcII) does not complete its life- cycle in R. prolixus. The relative AMP gene expressions were evaluated in the insect midgut and fat body infected on different days with the T. cruzi Dm 28c clone and the Y strain. The influence of the antibacterial activity on the intestinal microbiota was taken into account.

Methods

The presence of T. cruzi in the midgut of R. prolixus was analysed by optical microscope. The relative expression of the antimicrobial peptides encoding genes defensin (defA, defB, defC) and prolixicin (prol) was quantified by RT-qPCR. The antimicrobial activity of the AMPs against Staphylococcus aureus, Escherichia coli and Serratia marcescens were evaluated in vitro using turbidimetric tests with haemolymph, anterior and posterior midgut samples. Midgut bacteria were quantified using colony forming unit (CFU) assays and real time quantitative polymerase chain reaction (RT-qPCR).

Results

Our results showed that the infection of R. prolixus by the two different T. cruzi strains exhibited different temporal AMP induction profiles in the anterior and posterior midgut. Insects infected with T. cruzi Dm 28c exhibited an increase in defC and prol transcripts and a simultaneous reduction in the midgut cultivable bacteria population, Serratia marcescens and Rhodococcus rhodnii. In contrast, the T. cruzi Y strain neither induced AMP gene expression in the gut nor reduced the number of colony formation units in the anterior midgut. Beside the induction of a local immune response in the midgut after feeding R. prolixus with T. cruzi, a simultaneous systemic response was also detected in the fat body.

Conclusions

R. prolixus AMP gene expressions and the cultivable midgut bacterial microbiota were modulated in distinct patterns, which depend on the T. cruzi genotype used for infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1398-4) contains supplementary material, which is available to authorized users.

Tribolium castaneum defensins are primarily active against Gram-positive bacteria

The red flour beetle Tribolium castaneum is a destructive insect pest of stored food and feed products, and a model organism for development, evolutionary biology and immunity. The insect innate immune system includes antimicrobial peptides (AMPs) with a wide spectrum of targets including viruses, bacteria, fungi and parasites. Defensins are an evolutionarily-conserved class of AMPs and a potential new source of antimicrobial agents. In this context, we report the antimicrobial activity, phylogenetic and structural properties of three T. castaneum defensins (Def1, Def2 and Def3) and their relevance in the immunity of T. castaneum against bacterial pathogens. All three recombinant defensins showed bactericidal activity against Micrococcus luteus and Bacillus thuringiensis serovar tolworthi, but only Def1 and Def2 showed a bacteriostatic effect against Staphylococcus epidermidis. None of the defensins showed activity against the Gram-negative bacteria Escherichia coli and Pseudomonas entomophila or against the yeast Saccharomyces cerevisiae. All three defensins were transcriptionally upregulated following a bacterial challenge, suggesting a key role in the immunity of T. castaneum against bacterial pathogens. Phylogenetic analysis showed that defensins from T. castaneum, mealworms, Udo longhorn beetle and houseflies cluster within a well-defined clade of insect defensins. We conclude that T. castaneum defensins are primarily active against Gram-positive bacteria and that other AMPs may play a more prominent role against Gram-negative species.

Immune defence mechanisms of triatomines against bacteria, viruses, fungi and parasites

Triatomines are vectors that transmit the protozoan haemoflagellate Trypanosoma cruzi, the causative agent of Chagas disease. The aim of the current review is to provide a synthesis of the immune mechanisms of triatomines against bacteria, viruses, fungi and parasites to provide clues for areas of further research including biological control. Regarding bacteria, the triatomine immune response includes antimicrobial peptides (AMPs) such as defensins, lysozymes, attacins and cecropins, whose sites of synthesis are principally the fat body and haemocytes. These peptides are used against pathogenic bacteria (especially during ecdysis and feeding), and also attack symbiotic bacteria. In relation to viruses, Triatoma virus is the only one known to attack and kill triatomines. Although the immune response to this virus is unknown, we hypothesize that haemocytes, phenoloxidase (PO) and nitric oxide (NO) could be activated. Different fungal species have been described in a few triatomines and some immune components against these pathogens are PO and proPO. In relation to parasites, triatomines respond with AMPs, including PO, NO and lectin. In the case of T. cruzi this may be effective, but Trypanosoma rangeli seems to evade and suppress PO response. Although it is clear that three parasite-killing processes are used by triatomines - phagocytosis, nodule formation and encapsulation - the precise immune mechanisms of triatomines against invading agents, including trypanosomes, are as yet unknown. The signalling processes used in triatomine immune response are IMD, Toll and Jak-STAT. Based on the information compiled, we propose some lines of research that include strategic approaches of biological control.

Detection and preliminary physico-chemical properties of antimicrobial components in the native excretions/secretions of three species of Chrysomya (Diptera, Calliphoridae) in Brazil

Antibiotic-resistant bacteria in hospitals and communities increasingly threaten public health in Brazil and the rest of the World. There is an urgent need for additional antimicrobial drugs. Calliphorid blowfly larvae are a rich source of antimicrobial factors but the potential of Neotropical species has been neglected. This preliminary study evaluates the antimicrobial activity of the native excretions/secretions of larvae of three species of Brazilian calliphorids, Chrysomya megacephala, Chrysomya albiceps and Chrysomya putoria. Native excretions/secretions were collected from third instar larvae, sterile filtered and tested for antibacterial activity against Staphylococcus aureus 9518, Escherichia coli K12 4401 and Serratia marcescens 365. Turbidometric assays were made in micro-plates, using an ELISA reader, with readings taken up to 22 h. Bacterial suspensions at the start and end of each experiment were also serially diluted, spread on nutrient agar plates and then colony forming units counted. The physico-chemical characteristics of the native excretions/secretions were also tested by freezing/thawing, boiling, and protease digestion. The native excretions/secretions of larvae from these three Chrysomya species significantly inhibited bacterial growth. Therefore, Brazilian calliphorid flies could potentially provide new classes of antibiotics.

Assessing gene expression during pathogenesis: Use of qRT-PCR to follow toxin production in the entomopathogenic fungus Beauveria bassiana during infection and immune response of the insect host Triatoma infestans

Entomopathogenic fungi secrete toxic secondary metabolites during the invasion of the insect hemocoel as part of the infection process. Although these compounds have been frequently mentioned as virulence factors, the roles of many of them remain poorly understood, including the question of whether they are expressed during the infection process. A major hurdle to this issue remains the low sensitivity of biochemical detection techniques (e.g., HPLC) within the complex samples that may contain trace quantities of fungal molecules inside the insect. In this study, quantitative reverse transcription real-time PCR (qRT-PCR) was used to measure the transcript levels within the insect fungal pathogen Beauveria bassiana, that encode for the synthetase enzymes of the secondary metabolites tenellin (BbtenS), beauvericin (BbbeaS) and bassianolide (BbbslS) during the infection of Triatoma infestans, a Chagas disease insect vector. Absolute quantification was performed at different time periods after insect treatment with various concentrations of propagules, either by immersing the insects in conidial suspensions or by injecting them with blastospores. Both BbtenS and BbbeaS were highly expressed in conidia-treated insects at days 3 and 12 post-treatment. In blastospore-injected insects, BbtenS and BbbeaS expression peaked at 24h post-injection and were also highly expressed in insect cadavers. The levels of BbbslS transcripts were much lower in all conditions tested. The expression patterns of insect genes encoding proteins that belong to the T. infestans humoral immune system were also evaluated with the same technique. This qPCR-based methodology can contribute to decifering the dynamics of entomopathogenic fungal infection at the molecular level.

Rhodnius prolixus interaction with Trypanosoma rangeli: modulation of the immune system and microbiota population

BACKGROUND

Trypanosoma rangeli is a protozoan that infects a variety of mammalian hosts, including humans. Its main insect vector is Rhodnius prolixus and is found in several Latin American countries. The R. prolixus vector competence depends on the T. rangeli strain and the molecular interactions, as well as the insect's immune responses in the gut and haemocoel. This work focuses on the modulation of the humoral immune responses of the midgut of R. prolixus infected with T. rangeli Macias strain, considering the influence of the parasite on the intestinal microbiota.

METHODS

The population density of T. rangeli Macias strain was analysed in different R. prolixus midgut compartments in long and short-term experiments. Cultivable and non-cultivable midgut bacteria were investigated by colony forming unit (CFU) assays and by 454 pyrosequencing of the 16S rRNA gene, respectively. The modulation of R. prolixus immune responses was studied by analysis of the antimicrobial activity in vitro against different bacteria using turbidimetric tests, the abundance of mRNAs encoding antimicrobial peptides (AMPs) defensin (DefA, DefB, DefC), prolixicin (Prol) and lysozymes (LysA, LysB) by RT-PCR and analysis of the phenoloxidase (PO) activity.

RESULTS

Our results showed that T. rangeli successfully colonized R. prolixus midgut altering the microbiota population and the immune responses as follows: 1 - reduced cultivable midgut bacteria; 2 - decreased the number of sequences of the Enterococcaceae but increased those of the Burkholderiaceae family; the families Nocardiaceae, Enterobacteriaceae and Mycobacteriaceae encountered in control and infected insects remained the same; 3 - enhanced midgut antibacterial activities against Serratia marcescens and Staphylococcus aureus; 4 - down-regulated LysB and Prol mRNA levels; altered DefB, DefC and LysA depending on the infection (short and long-term); 5 - decreased PO activity.

CONCLUSION

Our findings suggest that T. rangeli Macias strain modulates R. prolixus immune system and modifies the natural microbiota composition.

A Kazal-type inhibitor is modulated by Trypanosoma cruzi to control microbiota inside the anterior midgut of Rhodnius prolixus

The triatomine insect, Rhodnius prolixus, is a vector of Trypanosoma cruzi, a protozoan parasite that causes Chagas disease. The parasite must overcome immune response and microbiota to develop inside the midgut of triatomines. In this study, we expressed, purified and characterized a Kazal-type inhibitor from the midgut of R. prolixus, named RpTI, which may be involved in microbiota - T. cruzi interactions. The qPCR showed that the RpTI transcript was primarily expressed in tissues from the intestinal tract and that it was upregulated in the anterior midgut after T. cruzi infection. A 315-bp cDNA fragment encoding the mature protein was cloned into the pPIC9 vector and expressed in Pichia pastoris system. Recombinant RpTI (rRpTI) was purified on a trypsin-Sepharose column and had a molecular mass of 11.5 kDa as determined by SDS-PAGE analysis. This protein inhibited trypsin (Ki = 0.42 nM), whereas serine proteases from the coagulation cascade were not inhibited. Moreover, trypanocidal assays revealed that rRpTI did not interfere in the viability of T. cruzi trypomastigotes. The RpTI transcript was also knocked down by RNA interference prior to infection of R. prolixus with T. cruzi. The amount of T. cruzi in the anterior midgut was significantly lower in RpTI knockdown insects compared to the non-silenced groups. We also verified that the bacterial load is higher in the anterior midgut of silenced and infected R. prolixus compared to non-silenced and infected insects. Our results suggest that T. cruzi infection increases the expression of RpTI to mediate microbiota modulation and is important for parasite immediately after infection with R. prolixus.

Anti-inflammatory activities of cecropin A and its mechanism of action

Cecropin A is a novel 37-residue cecropin-like antimicrobial peptide isolated from the cecropia moth, Hyalophora cecropia. We have demonstrated that cecropin A is an antibacterial agent and have investigated its mode of action. In this study, we show that cecropin A has potent antimicrobial activity against 2 multidrug resistant organisms-Acinetobacter baumanii and-Pseudomonas aeruginosa. Interactions between cecropin A and membrane phospholipids were studied using tryptophan blue shift experiments. Cecropin A has a strong interaction with bacterial cell mimetic membranes. These results imply that cecropin A has selectivity for bacterial cells. To address the potential the rapeutic efficacy of cecropin A, its anti-inflammatory activities and mode of action in mouse macrophage-derived RAW264.7 cells stimulated with lipopolysaccharide (LPS) were examined. Cecropin A suppressed nitrite production, mTNF-α, mIL-1β, mMIP-1, and mMIP-2 cytokine release in LPS-stimulated RAW264.7 cells. Furthermore, cecropin A inhibited intracellular cell signaling via the ERK, JNK, and p38 MAPK pathway, leading to the prevention of COX-2 expression in LPS-stimulated RAW264.7 cells. These results strongly suggest that cecropin A should be investigated as a potential agent for the prevention and treatment of inflammatory diseases.

Humoral responses in Rhodnius prolixus: bacterial feeding induces differential patterns of antibacterial activity and enhances mRNA levels of antimicrobial peptides in the midgut

BACKGROUND

The triatomine, Rhodnius prolixus, is a major vector of Trypanosoma cruzi, the causative agent of Chagas disease in Latin America. It has a strictly blood-sucking habit in all life stages, ingesting large amounts of blood from vertebrate hosts from which it can acquire pathogenic microorganisms. In this context, the production of antimicrobial peptides (AMPs) in the midgut of the insect is vital to control possible infection, and to maintain the microbiota already present in the digestive tract.

METHODS

In the present work, we studied the antimicrobial activity of the Rhodnius prolixus midgut in vitro against the Gram-negative and Gram-positive bacteria Escherichia coli and Staphylococcus aureus, respectively. We also analysed the abundance of mRNAs encoding for defensins, prolixicin and lysozymes in the midgut of insects orally infected by these bacteria at 1 and 7 days after feeding.

RESULTS

Our results showed that the anterior midgut contents contain a higher inducible antibacterial activity than those of the posterior midgut. We observed that the main AMP encoding mRNAs in the anterior midgut, 7 days after a blood meal, were for lysozyme A, B, defensin C and prolixicin while in the posterior midgut lysozyme B and prolixicin transcripts predominated.

CONCLUSION

Our findings suggest that R. prolixus modulates AMP gene expression upon ingestion of bacteria with patterns that are distinct and dependent upon the species of bacteria responsible for infection.

The effects of temperature and innate immunity on transmission of Campylobacter jejuni (Campylobacterales: Campylobacteraceae) between life stages of Musca domestica (Diptera: Muscidae)

The house fly (Musca domestica L.) is a well-established vector of human pathogens, including Campylobacter spp., which can cause infection of broiler chicken flocks, and through contaminated broiler meat can cause outbreaks of campylobacteriosis in humans. We investigated whether Campylobacter jejuni (Jones) could be transferred between life stages of M. domestica (larvae-pupae-adults) and determined bacterial counts of C. jejuni at different time points after bacterial exposure. C. jejuni was transmitted from infected larvae to pupae, but not to the adult stage. Infected larvae maintained at 25 degrees C had mean bacterial numbers of 6.5 +/- 0.2 SE log10 (colony forming units [CFU]/g) that subsequently dropped to 3.6 +/- 0.3 SE log10 (CFU/g) 8 h after infection. Pupae originating from infected larvae contained mean bacterial numbers of 5.3 +/- 0.1 SE log10 (CFU/g), and these numbers dropped to 4.8 +/- 0.1 SE log10 (CFU/g) 24 h after pupation. The decline in C. jejuni numbers during pupal development coincided with increased expression of antimicrobial peptides, including cecropin, diptericin, attacin, and defensin, in the larva-pupa transition stage and a later second peak in older pupae (4 or 48 h). Conversely, there was a reduced expression of the digestive enzyme, lysozyme, in pupae and adults compared with larvae.

Isolation and molecular characterization of a major hemolymph serpin from the triatomine, Panstrongylus megistus

Background

Chagas disease kills 2.5 thousand people per year of 15 million persons infected in Latin America. The disease is caused by the protozoan, Trypanosome cruzi, and vectored by triatomine insects, including Panstrongylus megistus, an important vector in Brazil. Medicines treating Chagas disease have unpleasant side effects and may be ineffective, therefore, alternative control techniques are required. Knowledge of the T. cruzi interactions with the triatomine host needs extending and new targets/strategies for control identified. Serine and cysteine peptidases play vital roles in protozoan life cycles including invasion and entry of T. cruzi into host cells. Peptidase inhibitors are, therefore, promising targets for disease control.

Methods

SDS PAGE and chromatograpy detected and isolated a P. megistus serpin which was peptide sequenced by mass spectrometry. A full amino acid sequence was obtained from the cDNA and compared with other insect serpins. Reverse transcription PCR analysis measured serpin transcripts of P. megistus tissues with and without T. cruzi infection. Serpin homology modeling used the Swiss Model and Swiss-PDB viewer programmes.

Results

The P. megistus serpin (PMSRP1) has a ca. 40 kDa molecular mass with 404 amino acid residues. A reactive site loop contains a highly conserved hinge region but, based on sequence alignment, the normal cleavage site for serine proteases at P1-P1′ was translocated to the putative position P4′-P5′. A small peptide obtained corresponded to the C-terminal 40 amino acid region. The secondary structure of PMSRP1 indicated nine α-helices and three β-sheets, similar to other serpins. PMSRP1 transcripts occurred in all tested tissues but were highest in the fat body and hemocytes. Levels of mRNA encoding PMSRP1 were significantly modulated in the hemocytes and stomach by T. cruzi infection indicating a role for PMSRP1 in the parasite interactions with P. megistus.

Conclusions

For the first time, a constitutively expressed serpin has been characterized from the hemolymph of a triatomine. This opens up new research avenues into the roles of serine peptidases in the T. cruzi/P. megistus association. Initial experiments indicate a role for PMSRP1 in T. cruzi interactions with P. megistus and will lead to further functional studies of this molecule.

An insight into the transcriptome of the digestive tract of the bloodsucking bug, Rhodnius prolixus

The bloodsucking hemipteran Rhodnius prolixus is a vector of Chagas' disease, which affects 7-8 million people today in Latin America. In contrast to other hematophagous insects, the triatomine gut is compartmentalized into three segments that perform different functions during blood digestion. Here we report analysis of transcriptomes for each of the segments using pyrosequencing technology. Comparison of transcript frequency in digestive libraries with a whole-body library was used to evaluate expression levels. All classes of digestive enzymes were highly expressed, with a predominance of cysteine and aspartic proteinases, the latter showing a significant expansion through gene duplication. Although no protein digestion is known to occur in the anterior midgut (AM), protease transcripts were found, suggesting secretion as pro-enzymes, being possibly activated in the posterior midgut (PM). As expected, genes related to cytoskeleton, protein synthesis apparatus, protein traffic, and secretion were abundantly transcribed. Despite the absence of a chitinous peritrophic membrane in hemipterans - which have instead a lipidic perimicrovillar membrane lining over midgut epithelia - several gut-specific peritrophin transcripts were found, suggesting that these proteins perform functions other than being a structural component of the peritrophic membrane. Among immunity-related transcripts, while lysozymes and lectins were the most highly expressed, several genes belonging to the Toll pathway - found at low levels in the gut of most insects - were identified, contrasting with a low abundance of transcripts from IMD and STAT pathways. Analysis of transcripts related to lipid metabolism indicates that lipids play multiple roles, being a major energy source, a substrate for perimicrovillar membrane formation, and a source for hydrocarbons possibly to produce the wax layer of the hindgut. Transcripts related to amino acid metabolism showed an unanticipated priority for degradation of tyrosine, phenylalanine, and tryptophan. Analysis of transcripts related to signaling pathways suggested a role for MAP kinases, GTPases, and LKBP1/AMP kinases related to control of cell shape and polarity, possibly in connection with regulation of cell survival, response of pathogens and nutrients. Together, our findings present a new view of the triatomine digestive apparatus and will help us understand trypanosome interaction and allow insights into hemipteran metabolic adaptations to a blood-based diet.

Single and mixed-species trypanosome and microsporidia infections elicit distinct, ephemeral cellular and humoral immune responses in honey bees

Frequently encountered parasite species impart strong selective pressures on host immune system evolution and are more apt to concurrently infect the same host, yet molecular impacts in light of this are often overlooked. We have contrasted immune responses in honey bees to two common eukaryotic endoparasites by establishing single and mixed-species infections using the long-associated parasite Crithidia mellificae and the emergent parasite Nosema ceranae. Quantitative polymerase chain reaction was used to screen host immune gene expression at 9 time points post inoculation. Systemic responses in abdomens during early stages of parasite establishment revealed conserved receptor (Down syndrome cell adhesion molecule, Dscam and nimrod C1, nimC1), signaling (MyD88 and Imd) and antimicrobial peptide (AMP) effector (Defensin 2) responses. Late, established infections were distinct with a refined 2 AMP response to C. mellificae that contrasted starkly with a 5 AMP response to N. ceranae. Mixed species infections induced a moderate 3 AMPs. Transcription in gut tissues highlighted important local roles for Dscam toward both parasites and Imd signaling toward N. ceranae. At both systemic and local levels Dscam, MyD88 and Imd transcription was consistently correlated based on clustering analysis. Significant gene suppression occurred in two cases from midgut to ileum tissue: Dscam was lowered during mixed infections compared to N. ceranae infections and both C. mellificae and mixed infections had reduced nimC1 transcription compared to uninfected controls. We show that honey bees rapidly mount complex immune responses to both Nosema and Crithidia that are dynamic over time and that mixed-species infections significantly alter local and systemic immune gene transcription.

Gene expression in gut symbiotic organ of stinkbug affected by extracellular bacterial symbiont

The bean bug Riptortus pedestris possesses a specialized symbiotic organ in a posterior region of the midgut, where numerous crypts harbor extracellular betaproteobacterial symbionts of the genus Burkholderia. Second instar nymphs orally acquire the symbiont from the environment, and the symbiont infection benefits the host by facilitating growth and by occasionally conferring insecticide resistance. Here we performed comparative transcriptomic analyses of insect genes expressed in symbiotic and non-symbiotic regions of the midgut dissected from Burkholderia-infected and uninfected R. pedestris. Expression sequence tag analysis of cDNA libraries and quantitative reverse transcription PCR identified a number of insect genes expressed in symbiosis- or aposymbiosis-associated patterns. For example, genes up-regulated in symbiotic relative to aposymbiotic individuals, including many cysteine-rich secreted protein genes and many cathepsin protease genes, are likely to play a role in regulating the symbiosis. Conversely, genes up-regulated in aposymbiotic relative to symbiotic individuals, including a chicken-type lysozyme gene and a defensin-like protein gene, are possibly involved in regulation of non-symbiotic bacterial infections. Our study presents the first transcriptomic data on gut symbiotic organ of a stinkbug, which provides initial clues to understanding of molecular mechanisms underlying the insect-bacterium gut symbiosis and sheds light on several intriguing commonalities between endocellular and extracellular symbiotic associations.

Differential expression profiles in the midgut of Triatoma infestans infected with Trypanosoma cruzi

Chagas disease, or American trypanosomiasis, is a parasitic disease caused by the protozoan Trypanosoma cruzi and is transmitted by insects from the Triatominae subfamily. To identify components involved in the protozoan-vector relationship, we constructed and analyzed cDNA libraries from RNA isolated from the midguts of uninfected and T. cruzi-infected Triatoma infestans, which are major vectors of Chagas disease. We generated approximately 440 high-quality Expressed Sequence Tags (ESTs) from each T. infestans midgut cDNA library. The sequences were grouped in 380 clusters, representing an average length of 664.78 base pairs (bp). Many clusters were not classified functionally, representing unknown transcripts. Several transcripts involved in different processes (e.g., detoxification) showed differential expression in response to T. cruzi infection. Lysozyme, cathepsin D, a nitrophorin-like protein and a putative 14 kDa protein were significantly upregulated upon infection, whereas thioredoxin reductase was downregulated. In addition, we identified several transcripts related to metabolic processes or immunity with unchanged expressions, including infestin, lipocalins and defensins. We also detected ESTs encoding juvenile hormone binding protein (JHBP), which seems to be involved in insect development and could be a target in control strategies for the vector. This work demonstrates differential gene expression upon T. cruzi infection in the midgut of T. infestans. These data expand the current knowledge regarding vector-parasite interactions for Chagas disease.