Studies on a haemolymph lectin isolated from Rhodnius prolixus and its interaction with Trypanosoma rangeli

Comparative proteomic analysis of the hemolymph and salivary glands of Rhodnius prolixus and R. colombiensis reveals candidates associated with differential lytic activity against Trypanosoma cruzi Dm28c and T. cruzi Y

BACKGROUND

Immune response of triatomines plays an important role in the success or failure of transmission of T. cruzi. Studies on parasite-vector interaction have shown the presence of trypanolytic factors and have been observed to be differentially expressed among triatomines, which affects the transmission of some T. cruzi strains or DTUs (Discrete Typing Units).

METHODOLOGY/PRINCIPAL FINDINGS

Trypanolytic factors were detected in the hemolymph and saliva of R. prolixus against epimastigotes and trypomastigotes of the Y strain (T. cruzi II). To identify the components of the immune response that could be involved in this lytic activity, a comparative proteomic analysis was carried out, detecting 120 proteins in the hemolymph of R. prolixus and 107 in R. colombiensis. In salivary glands, 1103 proteins were detected in R. prolixus and 853 in R. colombiensis. A higher relative abundance of lysozyme, prolixin, nitrophorins, and serpin as immune response proteins was detected in the hemolymph of R. prolixus. Among the R. prolixus salivary proteins, a higher relative abundance of nitrophorins, lipocalins, and triabins was detected. The higher relative abundance of these immune factors in R. prolixus supports their participation in the lytic activity on Y strain (T. cruzi II), but not on Dm28c (T. cruzi I), which is resistant to lysis by hemolymph and salivary proteins of R. prolixus due to mechanisms of evading oxidative stress caused by immune factors.

CONCLUSIONS/SIGNIFICANCE

The lysis resistance observed in the Dm28c strain would be occurring at the DTU I level. T. cruzi I is the DTU with the greatest geographic distribution, from the south of the United States to central Chile and Argentina, a distribution that could be related to resistance to oxidative stress from vectors. Likewise, we can say that lysis against strain Y could occur at the level of DTU II and could be a determinant of the vector inability of these species to transmit T. cruzi II. Future proteomic and transcriptomic studies on vectors and the interactions of the intestinal microbiota with parasites will help to confirm the determinants of successful or failed vector transmission of T. cruzi DTUs in different parts of the Western Hemisphere.

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.

Trypanosoma rangeli infection impairs reproductive success of Rhodnius prolixus

Trypanosoma rangeli is a protozoan that infects triatomines and mammals in Central and South America. Although it does not cause disease to humans, this parasite produces different levels of pathogenicity to its invertebrate host, mainly in species of the genus Rhodnius. In this study, we followed T. rangeli-infected and uninfected pairs throughout their adult lives and measured the amount of blood ingested, number of eggs laid, number of eggs hatched and proportion of infertile eggs, as well as female life expectancy. We found that all reproductive parameters were drastically decreased during infection, mainly due to the reduced amount of blood the infected insects ingested throughout their lives. Reproductive parameters were also affected by the reduction of the life expectancy of infected females, as survival was positively correlated with the number of eggs laid. The strategies used by the parasite to be transmitted are discussed in view of the pathological effects it causes in the insect.

The innate immune response of triatomines against Trypanosoma cruzi and Trypanosoma rangeli with an unresolved question: Do triatomines have immune memory?

The present work aimed to review the immune response from different triatomines against Trypanosoma cruzi and Trypanosoma rangeli and propose the study of immune memory in such insects. Trypanosoma use triatomines as vectors to reach and infect mammals. A key question to be answered about vector-parasite interaction is why the immune defense and resistance of the insect against the parasites vary. Up to date data shows that the defense of triatomines against parasites includes cellular (phagocytosis, nodulation and encapsulation) and humoral (antimicrobial peptides, phenoloxidase and reactive oxygen and nitrogen species) responses. The immune response varies depending on the triatomine species, the trypanosome strain and species, and the insect intestinal microbiota. Despite significant advances to understand parasite-insect interaction, it is still unknown if triatomines have immune memory against parasites and if this memory may derive from tolerance to parasites attack. Therefore, a closer study of such interaction could contribute and establish new proposals to control the parasite at the vector level to reduce parasite transmission to mammals, including men. For instance, if immune memory exists in the triatomines, it would be interesting to induce weak infections in insects to find out if subsequent infections are less intense and if the insects succeed in eliminating the parasites.

Isolation, characterization of galactose-specific lectin from Odoiporus longicollis and its antibacterial and anticancer activities

Lectins are renowned hemagglutinins and multivalent proteins with a well known quality for sugar-binding specificity that participate significantly in invertebrate defense functions. Studies on biological activity of lectin from coleopteran insect are very scarce. In this study, lectin from the hemolymph in the grub of banana pest, Odoiporus longicollis was subjected to purification, biochemical and functional characterizations. The lectin was purified by PEG precipitation and ion-exchange chromatography using Q-Sepharose as a matrix. The purified lectin showed hemagglutination activity against rat erythrocytes, heat-labile, cation independent and insensitive to EDTA. Further, the carbohydrate affinity of this lectin was found with mannitol, adonitol, L-arabinose, L-rhamnose, D-galactose and sorbitol. The native form of purified lectin was calculated as 360 kDa by FPLC system. Denatured gel electrophoresis of the purified lectin consisted of five distinct polypeptides with molecular weights approximately 160, 60, 52, 40 and 38 kDa, respectively. The amino acid sequences obtained through peptide mass fingerprinting analysis exhibited homologies to the known conserved regions of galactose binding lectins. Further, the purified lectin exhibited bacterial inhibition with LPS from Serratia marcescens. In addition, isolated lectin also exerted bacterial agglutination, antibacterial and anti-proliferative activity against Mycobacterium smegmatis, Bacillus pumilus and Neuro 2a cell line, respectively.

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.

Glycosylation on proteins of the intestine and perimicrovillar membrane of Triatoma (Meccus) pallidipennis, under different feeding conditions

Trypanosoma cruzi, the causative agent of Chagas disease, interacts with molecules in the midgut of its insect vector to multiply and reach the infective stage. Many studies suggest that the parasite binds to midgut-specific glycans. We identified several glycoproteins expressed in the intestine and perimicrovillar membrane (PMM) of Triatoma (Meccus) pallidipennis under different feeding conditions. In order to assess changes in protein-linked glycans, we performed lectin and immunoblot analyses on glycoprotein extracts from these intestinal tissues using well-characterized lectins, and an antibody, which collectively recognize a wide range of different glycans epitopes. We observed that the amount and composition of proteins and glycoproteins associated with different glycans structures changed over time in the intestines and PMM under different physiological conditions. PMM extracts contained a wide variety of glycoproteins with different sugar residues, including abundant high-mannose and complex sialylated glycans. We propose that these molecules could be involved in the process of parasite-vector interactions.

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.

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.

Triatomine physiology in the context of trypanosome infection

Triatomines are hematophagous insects that feed on the blood of vertebrates from different taxa, but can occasionally also take fluids from invertebrate hosts, including other insects. During the blood ingestion process, these insects can acquire diverse parasites that can later be transmitted to susceptible vertebrates if they complete their development inside bugs. Trypanosoma cruzi, the etiological agent of Chagas disease, and Trypanosoma rangeli are protozoan parasites transmitted by triatomines, the latter only transmitted by Rhodnius spp. The present work makes an extensive revision of studies evaluating triatomine-trypanosome interaction, with special focus on Rhodnius prolixus interacting with the two parasites. The sequences of events encompassing the development of these trypanosomes inside bugs and the consequent responses of insects to this infection, as well as many pathological effects produced by the parasites are discussed.

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.

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.

Characterization of multisugar-binding C-type lectin (SpliLec) from a bacterial-challenged cotton leafworm, Spodoptera littoralis

Background

Various proteins that display carbohydrate-binding activity in a Ca²⁺-dependent manner are classified into the C-type lectin family. They have one or two C-type carbohydrate-recognition domains (CRDs) composed of 110–130 amino acid residues in common. C-type lectins mediate cell adhesion, non-self recognition, and immuno-protection processes in immune responses and thus play significant roles in clearance of invaders, either as cell surface receptors for microbial carbohydrates or as soluble proteins existing in tissue fluids. The lectin of Spodoptera littoralis is still uncharacterized.

Methodology

A single orf encoding a deduced polypeptide consisting of an 18-residue signal peptide and a 291-residue mature peptide, termed SpliLec, was isolated from the haemolymph of the cotton leafworm, S. littoralis, after bacterial challenge using RACE-PCR. Sequence analyses of the data revealed that SpliLec consists of two CRDs. Short-form CRD₁ and long-form CRD₂ are stabilized by two and three highly conserved disulfide bonds, respectively. SpliLec shares homology with some dipteran lectins suggesting possible common ancestor. The purified SpliLec exhibited a 140-kDa molecular mass with a subunit molecular mass of 35 kDa. The hemagglutination assays of the SpliLec confirmed a thermally stable, multisugar-binding C-type lectin that binds different erythrocytes. The purified SpliLec agglutinated microorganisms and exhibited comparable antimicrobial activity against gram (+) and gram (−) bacteria too.

Conclusions

Our results suggested an important role of the SpliLec gene in cell adhesion and non-self recognition. It may cooperate with other AMPs in clearance of invaders of Spodoptera littoralis.

Parasite-mediated interactions within the insect vector: Trypanosoma rangeli strategies

Trypanosoma rangeli is a protozoan that is non-pathogenic for humans and other mammals but causes pathology in the genus Rhodnius. T. rangeli and R. prolixus is an excellent model for studying the parasite-vector interaction, but its cycle in invertebrates remains unclear. The vector becomes infected on ingesting blood containing parasites, which subsequently develop in the gut, hemolymph and salivary glands producing short and large epimastigotes and metacyclic trypomastigotes, which are the infective forms. The importance of the T. rangeli cycle is the flagellate penetration into the gut cells and invasion of the salivary glands. The establishment of the parasite depends on the alteration of some vector defense mechanisms. Herein, we present our understanding of T. rangeli infection on the vector physiology, including gut and salivary gland invasions, hemolymph reactions and behavior alteration.

Genetics and evolution of triatomines: from phylogeny to vector control

Triatomines are hemipteran bugs acting as vectors of the protozoan parasite Trypanosoma cruzi. This parasite causes Chagas disease, one of the major parasitic diseases in the Americas. Studies of triatomine genetics and evolution have been particularly useful in the design of rational vector control strategies, and are reviewed here. The phylogeography of several triatomine species is now slowly emerging, and the struggle to reconcile the phenotypic, phylogenetic, ecological and epidemiological species concepts makes for a very dynamic field. Population genetic studies using different markers indicate a wide range of population structures, depending on the triatomine species, ranging from highly fragmented to mobile, interbreeding populations. Triatomines transmit T. cruzi in the context of complex interactions between the insect vectors, their bacterial symbionts and the parasites; however, an integrated view of the significance of these interactions in triatomine biology, evolution and in disease transmission is still lacking. The development of novel genetic markers, together with the ongoing sequencing of the Rhodnius prolixus genome and more integrative studies, will provide key tools to expanding our understanding of these important insect vectors and allow the design of improved vector control strategies.

Trypanosoma rangeli: a new perspective for studying the modulation of immune reactions of Rhodnius prolixus

Insects are exposed to a wide range of microorganisms (bacteria, fungi, parasites and viruses) and have interconnected powerful immune reactions. Although insects lack an acquired immune system they have well-developed innate immune defences that allow a general and rapid response to infectious agents.

Over the last few decades we have observed a dramatic increase in the knowledge of insect innate immunity, which relies on both humoral and cellular responses. However, innate reactions to natural insect pathogens and insect-transmitted pathogens, such as parasites, still remain poorly understood.

In this review, we briefly introduce the general immune system of insects and highlight our current knowledge of these reactions focusing on the interactions of Trypanosoma rangeli with Rhodnius prolixus, an important model for innate immunity investigation.

Triatominae-Trypanosoma cruzi/T. rangeli: Vector-parasite interactions

Of the currently known 140 species in the family Reduviidae, subfamily Triatominae, those which are most important as vectors of the aetiologic agent of Chagas disease, Trypanosoma cruzi, belong to the tribes Triatomini and Rhodniini. The latter not only transmit T. cruzi but also Trypanosoma rangeli, which is considered apathogenic for the mammalian host but can be pathogenic for the vectors. Using different molecular methods, two main lineages of T. cruzi have been classified, T. cruzi I and T. cruzi II. Within T. cruzi II, five subdivisions are recognized, T. cruzi IIa-IIe, according to the variability of the ribosomal subunits 24Salpha rRNA and 18S rRNA. In T. rangeli, differences in the organization of the kinetoplast DNA separate two forms denoted T. rangeli KP1+ and KP1-, although differences in the intergenic mini-exon gene and of the small subunit rRNA (SSU rRNA) suggest four subpopulations denoted T. rangeli A, B, C and D. The interactions of these subpopulations of the trypanosomes with different species and populations of Triatominae determine the epidemiology of the human-infecting trypanosomes in Latin America. Often, specific subpopulations of the trypanosomes are transmitted by specific vectors in a particular geographic area. Studies centered on trypanosome-triatomine interaction may allow identification of co-evolutionary processes, which, in turn, could consolidate hypotheses of the evolution and the distribution of T. cruzi/T. rangeli-vectors in America, and they may help to identify the mechanisms that either facilitate or impede the transmission of the parasites in different vector species. Such mechanisms seem to involve intestinal bacteria, especially the symbionts which are needed by the triatomines to complete nymphal development and to produce eggs. Development of the symbionts is regulated by the vector. T. cruzi and T. rangeli interfere with this system and induce the production of antibacterial substances. Whereas T. cruzi is only subpathogenic for the insect host, T. rangeli strongly affects species of the genus Rhodnius and this pathogenicity seems based on a reduction of the number of symbionts.

Rhodnius prolixus: identification of immune-related genes up-regulated in response to pathogens and parasites using suppressive subtractive hybridization

We report the identification of immune-related molecules from the fat body, and intestine of Rhodnius prolixus, an important vector of Chagas disease. Insects were challenged by introducing pathogens or Trypanosoma cruzi, the parasite that causes Chagas disease, into the hemocoel. RNA from intestines, or fat body were isolated 24h after stimulation. We used suppressive subtractive hybridization to identify immune-related genes, generated three subtracted libraries, sequenced the clones and assembled the sequences. The functional annotation revealed expressed sequence tags (ESTs) generated in response to various stimuli in all tissues, and included pathogen recognition molecules, regulatory molecules, and effector molecules.

Purification and characterization of a lectin from the banana shrimp Fenneropenaeus merguiensis hemolymph

A lectin from the hemolymph of the banana shrimp Fenneropenaeus merguiensis was purified by affinity chromatography on a fetuin-agarose column following by gel filtration on a Superose-12 column. The native molecular mass of purified F. merguiensis lectin (FmL) determined by gel filtration was 316.2 kDa and its carbohydrate content was estimated to be 4.4%. By SDS-PAGE analysis, purified FmL consisted of 32.3 kDa and 30.9 kDa subunits. These data suggest that this lectin is an oligomer. Two-dimensional electrophoresis showed that it had a pI value of 6.0 and was mainly composed of glycine, serine, histidine, glutamic acids and glutamine, with relatively lower amounts of methionine and tyrosine. Purified FmL expressed higher agglutination activity against rabbit and rat erythrocytes than with those from human, and its activity was Ca(2+)-dependent. The hemagglutinating activity of FmL was stable up to 55 degrees C and at pH 7.5-8. N-acetylated sugars, such as ManNAc, GlcNAc, GalNAc, and NeuNAc were strong inhibitors of the FmL induced hemagglutinating activity with NeuNAc being most effective. Porcine stomach mucin and fetuin were the most potent inhibitors of FmL. Purified FmL caused selective agglutination of Vibrio harveyi, and Vibrio parahemolyticus both pathogens of this Penaeus species and to a lesser extent Vibrio vulnificus but had no effect on the non-pathogenic strains; Vibrio cholerae, Salmonella typhi and Escherichia coli. Its bacterial agglutination was also completely inhibited by NeuNAc, mucin, fetuin and also anti-FmL antibody. This observation indicates that FmL may contribute to the defense response of this species of penaeid shrimps to potentially pathogenic bacteria.

Participation of a galactose-specific C-type lectin in Drosophila immunity

A galactose-specific C-type lectin has been purified from a pupal extract of Drosophila melanogaster. This lectin gene, named DL1 (Drosophila lectin 1), is part of a gene cluster with the other two galactose-specific C-type lectin genes, named DL2 (Drosophila lectin 2) and DL3 (Drosophila lectin 3). These three genes are expressed differentially in fruit fly, but show similar haemagglutinating activities. The present study characterized the biochemical and biological properties of the DL1 protein. The recombinant DL1 protein bound to Escherichia coli and Erwinia chrysanthemi, but not to other Gram-negative or any other kinds of microbial strains that have been investigated. In addition, DL1 agglutinated E. coli and markedly intensified the association of a Drosophila haemocytes-derived cell line with E. coli. For in vivo genetic analysis of the lectin genes, we also established a null-mutant Drosophila. The induction of inducible antibacterial peptide genes was not impaired in the DL1 mutant, suggesting that the galactose-specific C-type lectin does not participate in the induction of antibacterial peptides, but possibly participates in the immune response via the haemocyte-mediated mechanism.

Trypanosoma rangeli interactions within the vector Rhodnius prolixus: a mini review

This article is an integrative mini review of the research on the interactions between Trypanosoma rangeli and the insect vector, Rhodnius prolixus. Special attention is given to the interactions of these parasites with the gut environment, gut walls, with hemolymph invasion, hemocytes, hemocyte microaggregations, prophenoloxidase-activating system, superoxide, and nitric acid generation and eicosanoid pathways. We described factors affecting vectorial capacity and suggested that T. rangeli may modulate the hemocoelic invasion and the survival of the parasites by overcoming the cellular and humoral defense reactions of the insect vector at different physiological events. The mechanisms of these interactions and their significance for parasite transmission are discussed.

Towards an understanding of the interactions of Trypanosoma cruzi and Trypanosoma rangeli within the reduviid insect host Rhodnius prolixus

This review outlines aspects on the developmental stages of Trypanosoma cruzi and Trypanosoma rangeli in the invertebrate host, Rhodnius prolixus. Special attention is given to the interactions of these parasites with gut and hemolymph molecules and the effects of the organization of midgut epithelial cells on the parasite development. The vector insect's permissiveness to T. cruzi, which develops in the vector gut, largely depends on the host nutritional state, the parasite strain and the molecular interactions with trypanolytic compounds, lectins and resident bacteria in the gut. T. rangeli invades the hemocoel and once in the hemolymph, can be recognized and activates the defense system of its insect vector, i.e., the prophenoloxidase system, phagocytosis, hemocyte microaggregation, superoxide and nitric oxide activity and the eicosanoid biosynthesis pathway. Taken together, these findings not only provide a better understanding of the interactions parasite-insect vector, but also offer new insights into basic physiological processes involved in the parasites transmission.

A role for insect galectins in parasite survival

Insect galectins are associated with embryonic development or immunity against pathogens. Here, we show that they can be exploited by parasites for survival in their insect hosts. PpGalec, a tandem repeat galectin expressed in the midgut of the sandfly Phlebotomus papatasi, is used by Leishmania major as a receptor for mediating specific binding to the insect midgut, an event crucial for parasite survival, and accounts for species-specific vector competence for the most widely distributed form of cutaneous leishmaniasis in the Old World. In addition, these studies demonstrate the feasibility of using midgut receptors for parasite ligands as target antigens for transmission-blocking vaccines.

TsetseEP, a gut protein from the tsetse Glossina morsitans, is related to a major surface glycoprotein of trypanosomes transmitted by the fly and to the products of a Drosophila gene family

African trypanosomes live in the lumen of the gut of tsetse (Glossina) and may have to face an immune response. As yet, it is unclear whether they are sensitive to antimicrobial peptides in vivo, but for some years there has been indirect evidence that one or more lectins can influence the infection. We have purified a protein complex from midgut extracts that, by SDS-PAGE, is a doublet of 37 and 38 kDa in a ratio of 3:1. Through prediction from corresponding cDNA clones, the full-length protein (tsetseEP) contains 320 amino acids, including a signal peptide. There is apparently only one gene encoding this protein. Towards the C terminus, the protein contains a run of 59 (EP) repeats, which surprisingly is what comprises almost the entire mature EP procyclin molecule present on the surface of trypanosomes in the tsetse gut. Drosophila contains a number of genes encoding proteins, of unknown function, with the same cysteine pattern as tsetseEP; this pattern is not reported for any other protein. Immunoblotting with a monoclonal antibody against (EP) repeats reveals expression in the gut, but not salivary glands, of female and male flies, whether or not fed. Immunoelectron microscopy shows the presence in vesicles in midgut cells and in the lumen of the gut. Attempts to demonstrate lectin activity were thwarted by limited availability of the protein complex.

Characterization of an ecto-phosphatase activity in malpighian tubules of hematophagous bug Rhodnius prolixus

We have characterized a phosphatase activity present on the external surface of intact Malpighian tubules in Rhodnius prolixus. This phosphatase hydrolyses the substrate p-nitrophenyl phosphate at a rate of 3.38 +/- 0.07 nmol Pi x mg(-1) x min(-1). Phosphatase activity decreased with the increase of the pH from 6.4 to 7.6 pH, a range in which tubules cellular integrity was maintained for at least 1 h. Classical inhibitors of acid phosphatase, such as ammonium molybdate, fluoride, vanadate, mpV-PIC, and bpV-PHEN, caused different patters of inhibition. The ecto-phosphatase present an apparent Km of 1.67 +/- 0.34 mM and Vmax of 5.71 +/- 0.37 nmol Pi x mg(-1) x min(-1) for p-NPP. Zinc chloride inhibited 78.2% of ecto-phosphatase activity, with Ki of 0.35 mM. Such inhibition was reversed by incubation with cysteine and GSH, but not DTT, serine, and GSSG, showing that cysteine residues are important for enzymatic activity. Phosphatase activity increased 141% three days after blood meal, and returned to basal levels 2 days later. These results suggest that ecto-phosphatase activity could be involved in a diuretic mechanism, essential in the initial days after a blood meal for the control of Rhodnius homeostasis.

Suppression of the prophenoloxidase system in Rhodnius prolixus orally infected with Trypanosoma rangeli

Investigations were carried out to compare aspects of the prophenoloxidase (proPO)-activating pathway in Rhodnius prolixus hemolymph in response to oral infection and inoculation of the insects with two developmental forms of Trypanosoma rangeli epimastigotes strain H14. In vivo experiments demonstrated that in control insects fed on uninfected blood, inoculation challenge with short epimastigotes resulted in high phenoloxidase (PO) activity. In contrast, previous feeding on blood containing either short or long epimastigotes was able to suppress the proPO activation induced by thoracic inoculation of the short forms. In vitro assays in the presence of short epimastigotes demonstrated that control hemolymph or hemolymph provided by insects previously fed on blood containing epimastigotes incubated with fat body homogenates from control insects significantly increased the PO activity. However, fat body homogenates from insects previously fed on blood containing epimastigotes, incubated with hemolymph taken from insects fed on control blood or blood infected with epimastigotes, drastically reduced the proPO activation. The proteolytic activity in the fat body homogenates of control insects was significantly higher than in those obtained from fat body extracts of insects previously fed on blood containing epimastigotes. These findings indicate that the reduction of the proteolytic activities in the fat body from insects fed on infected blood no longer allows a significant response of the proPO system against parasite challenge. It also provides a better understanding of T. rangeli infection in the vector and offer novel insights into basic immune processes in their invertebrate hosts.

Isolation and characterization of an acetyl group-recognizing agglutinin from the serum of the Indian white shrimp Fenneropenaeus indicus

A natural agglutinin from the serum of the Indian white shrimp Fenneropenaeus (Penaeus) indicus was purified to electrophoretic homogeneity by a single-step affinity chromatography on N-acetylglucosamine-Sepharose 6B. The expression of hemagglutinating (HA) activity of F. indicus agglutinin (FIA) was independent of the presence of divalent cations and insensitive to their chelators. FIA gave a single symmetrical peak in its native form with a molecular mass estimate of 200 kDa on gel filtration in HPLC, and SDS-PAGE under reducing conditions revealed that it is a homo-oligomer of a 27-kDa subunit protein. The pattern of reactivity of FIA against anti-FIA rabbit serum in immunodiffusion and immunoelectrophoretic analysis provided additional evidence for its purity and homogeneity. HA-inhibition studies documented exclusive specificity of FIA for acetyl groups in carbohydrates independently of the presence of these groups at the C-2 or C-5 position and its stereochemical arrangement in the axial or equatorial orientation. The unique ability of FIA to recognize acetyl groups was also explicitly demonstrated with sialo- and asialo-glycoproteins. Strikingly, FIA also interacted equally with amino acids and chemicals containing acetyl groups, thereby unambiguously demonstrating the exquisite specificity of FIA for an acetyl group, irrespective of the presence of this group in carbohydrate or noncarbohydrate ligands. The susceptibility of HA activity of FIA to inhibition by lipopolysaccharides from diverse gram-negative bacteria as well as its ability to selectively agglutinate several bacterial species isolated from infected shrimps implicate a potential role of this humoral agglutinin of F. indicus in the host immunodefense reactions against microbial invaders.

Influence of calcium on Manduca sexta plasmatocyte spreading and network formation

Plasmatocytes are a class of insect hemocytes important in the cellular defense response. In some species, they are phagocytic, protecting the insect from smaller pathogens. In many insects, they work in concert with other hemocytes (particularly other plasmatocytes and granular cells) to form nodules and to encapsulate foreign material. To perform these functions, plasmatocytes attach to, spread on, and surround suitable targets. Because of their importance, because we had previously observed that prolonged incubation of hemocytes in solutions containing the divalent cation chelator ethylenediaminetetraacetic acid (EDTA) inhibited plasmatocyte spreading, and because of the importance of divalent cations in many immune-related functions, we investigated the effect of calcium and magnesium on spreading of plasmatocytes from fifth instar Manduca sexta larvae. On glass slides, plasmatocytes spread more quickly and elongated in Grace's medium containing 5 mM calcium, compared to calcium-free medium. In the presence of calcium, plasmatocyte adhesion, spreading, and network formation were not visibly different in magnesium-free and magnesium-containing Grace's medium. Using immunomicroscopy with a monoclonal antibody specific for plasmatocytes, we measured the length and width of plasmatocytes incubated with several different concentrations of calcium. Plasmatocyte length positively correlated with calcium concentration to 5 mM (maximum concentration tested and approximately the hemolymph concentration). Mean plasmatocyte width was less in 0 and 5 mM calcium than in 0.05 or 0.5 mM calcium. On plastic, hemocytes survived longer than on glass (they survived beyond 24 h) and, in 5 mM calcium, formed an extensive network readily visible by phase-contrast microscopy. This network was never as extensive in the absence of calcium. Network formation in the absence of magnesium, but presence of calcium, resembled network formation in standard Grace's medium.

Identification and distribution of carbohydrate moieties on the salivary glands of Rhodnius prolixus and their possible involvement in attachment/invasion by Trypanosoma rangeli

In the present study, FITC-labelled lectins (WGA, Con A, PNA, HPA, and TPA) were utilized to investigate carbohydrate residues on the surface of Rhodnius prolixus salivary glands. The results revealed that the salivary glands are rich in carbohydrate moieties and the diversity in binding pattern of particular lectins showed the presence of specific carbohydrate residues in the basal lamina, muscle, and cell layers of the glands. Subsequently, the sugars detected on the salivary gland surface were employed to investigate the interaction between Trypanosoma rangeli and the R. prolixus salivary glands. In vitro adhesion inhibition assays using long epimastigote forms (the invasion/adhesion forms) showed that some sugars tested were able to block the receptors on both the surfaces of the salivary glands and on T. rangeli. Among the sugars tested, GlcNAc, GalNAc, and galactose showed the highest overall inhibitory effect, following pre-incubation of either the salivary glands or parasites. These results are discussed in relation to previous work on the role of carbohydrates and lectins in insect vector/parasite interactions.

Immune response of Drosophila melanogaster to infection with the flagellate parasite Crithidia spp

Insects are able to recognize invading microorganisms and to mount an immune response to bacterial and fungal infections. Recently, the fruitfly Drosophila melanogaster has emerged as a promising invertebrate model to investigate innate immunity because of its well-characterized genetics. Insects are also vectors of numerous parasites which can trigger an immune response. We have investigated the interaction of Drosophila melanogaster with the flagellate protozoan Crithidia spp. We show that a per os parasitic infection triggers the synthesis of several antimicrobial peptides. By reverse phase HPLC and mass spectrometry, peptides were shown to be present in the hemolymph and not in the gut tissue, suggesting the presence of immune messengers between the site of the infection, namely the gut, and the fat body, the main site of synthesis for antimicrobial peptides. Interestingly, we have identified one molecule which is specifically induced in the hemolymph after infection with Crithidia, but not with bacteria, suggesting that Drosophila can discriminate between pathogens. When flagellates were injected into the hemolymph, a low synthesis of antimicrobial peptides was observed together with phagocytosis of parasites by circulating hemocytes. The data presented here suggest that Drosophila-Crithidia spp. represents an interesting model to study host defense against protozoan parasites.

Isolation and characterization of Dorin M, a lectin from plasma of the soft tick Ornithodoros moubata

A lectin with high hemagglutinating activity, which we have named Dorin M, was identified in the plasma of the soft tick Ornithodoros moubata. The activity of the plasma lectin could be efficiently inhibited by sialic acid, N-acetyl-D-hexosamines and sialoglycoproteins. Dorin M was purified to homogeneity using two different isolation systems: affinity chromatography on a column of bovine submaxillary mucin conjugated to Sepharose 4B with specific elution by N-acetyl-D-glucosamine and chromatography on Blue-Sepharose followed by anion exchange FPLC on a MonoQ column. The purified lectin is a glycoprotein which, in the native state, forms aggregates with molecular mass of about 640 kDa. Non-reducing SDS PAGE revealed that the lectin consists of two noncovalently bound subunits migrating closely around 37 kDa. Dorin M is a glycoprotein, probably modified by N-type glycosylation. After chemical deglycosylation, only one band of about 32 kDa was detected. Dorin M is the first lectin purified from ticks.

Metalloproteases in Trypanosoma rangeli-infected Rhodnius prolixus

Protease activities in the haemolymph and fat body in a bloodsucking insect, Rhodnius prolixus, infected with Trypanosoma rangeli, were investigated. After SDS-polyacrylamide gel electrophoresis containing gelatin as substrate, analysis of zymograms performed on samples of different tissues of controls and insects inoculated or orally infected with short or long epimastigotes of T. rangeli, demonstrated distinct patterns of protease activities: (i) proteases were detected in the haemolymph of insects which were fed on, or inoculated with, short epimastigotes of T. rangeli (39 kDa and 33 kDa, respectively), but they were not observed in the fat body taken from these insects; (ii) protease was also presented in the fat bodies derived from naive insects or controls inoculated with sterile phosphate-saline buffer (49 kDa), but it was not detected in the haemolymph of these insects; (iii) no protease activity was observed in both haemolymph and fat bodies taken from insects inoculated with, or fed on, long epimastigotes of T. rangeli. Furthermore, in short epimastigotes of T. rangeli extracts, three bands of the protease activities with apparent molecular weights of 297, 198 and 95 kDa were detected while long epimastigotes preparation presented only two bands of protease activities with molecular weights of 297 and 198 kDa. The proteases from the insect infected with T. rangeli and controls belong to the class of either metalloproteases or metal-activated enzymes since they are inhibited by 1,10-phenanthroline. The significance of these proteases in the insects infected with short epimastigotes of T. rangeli is discussed in relation to the success of the establishment of infection of these parasites in its vector, R. prolixus.