Antimicrobial properties of Anopheles albimanus pericardial cells

Localization of nitric oxide-producing hemocytes in Aedes and Culex mosquitoes infected with bacteria

Mosquitoes are significant vectors of various pathogens. Unlike vertebrates, insects rely solely on innate immunity. Hemocytes play a crucial role in the cellular part of the innate immune system. The gaseous radical nitric oxide (NO) produced by hemocytes acts against pathogens and also functions as a versatile transmitter in both the immune and nervous systems, utilizing cyclic guanosine monophosphate (cGMP) as a second messenger. This study conducted a parallel comparison of NO synthase (NOS) expression and NO production in hemocytes during Escherichia coli K12 infection in four vector species: Aedes aegypti, Aedes albopictus, Culex pipiens molestus, and Culex pipiens quinquefasciatus. Increased NOS expression by NADPH diaphorase (NADPHd) staining and NO production by immunofluorescence against the by-product L-citrulline were observed in infected mosquito hemocytes distributed throughout the abdomens. NADPHd activity and citrulline labeling were particularly found in periostial hemocytes near the heart, but also on the ventral nerve chord (VNC). Pericardial cells of Ae. aegypti and Cx. p. molestus showed increased citrulline immunofluorescence, suggesting their involvement in the immune response. Oenocytes displayed strong NADPHd and citrulline labeling independent of infection status. This comparative study, consistent with findings in other species, suggests a widespread phenomenon of NO's role in hemocyte responses during E. coli infection. Found differences within and between genera highlight the importance of species-specific investigations.

Toxic effect of Cd burden on the gut microflora and immune responses of wolf spider Pardosa pseudoannulata

Spiders are dominant predators in the paddy ecosystem, but the immunotoxicity induced by environmental contaminants like heavy metals is still largely unknown. The gut microbiota-host interaction was the basic immune mechanism discovered in the arthropods. Here, we investigated the gut microflora and immune responses of wolf spider Pardosa pseudoannulata under Cd burden. Cd exposure was identified to shape the gut microbial community structure of spiders, with increased levels of Firmicutes and pathogens, and decreased levels of Proteobacteria and Bacteroidota. The alteration of microbiota-derived immune messengers like peptidoglycan (PGN) was also observed. ELISA and hemolymph metabolomic analysis showed that the activities of immune effectors phenoloxidase (PO) and lysozyme (LZM) and the abundance of tyrosine derivates were decreased, which indicated the suppression of Cd on the melanization immune response of spiders. Correlation analysis revealed a close relationship between the impaired immune system and the disordered microbiota. This study provides insight into the underlying mechanisms of the gut microflora-immune system interaction of P. pseudoannulata in response to Cd burden.

Mosquito pericardial cells upregulate Cecropin expression after an immune challenge

Most mosquito-transmitted pathogens grow or replicate in the midgut before invading the salivary glands. Pathogens are exposed to several immunological factors along the way. Recently, it was shown that hemocytes gather near the periostial region of the heart to efficiently phagocytose pathogens circulating in the hemolymph. Nerveless, not all pathogens can be phagocyted by hemocytes and eliminated by lysis. Interestingly, some studies have shown that pericardial cells (PCs) surrounding periostial regions, may produce humoral factors, such as lysozymes. Our current work provides evidence that Anopheles albimanus PCs are a major producer of Cecropin 1 (Cec1). Furthermore, our findings reveal that after an immunological challenge, PCs upregulate Cec1 expression. We conclude that PCs are positioned in a strategic location that could allow releasing humoral components, such as cecropin, to lyse pathogens on the heart or circulating in the hemolymph, implying that PCs could play a significant role in the systemic immune response.

Differential Production of Nitric Oxide and Hydrogen Peroxide among Drosophila melanogaster, Apis mellifera, and Mamestra brassicae Immune-Activated Hemocytes after Exposure to Imidacloprid and Amitraz

Invertebrates have a diverse immune system that responds differently to stressors such as pesticides and pathogens, which leads to different degrees of susceptibility. Honeybees are facing a phenomenon called colony collapse disorder which is attributed to several factors including pesticides and pathogens. We applied an in vitro approach to assess the response of immune-activated hemocytes from Apis mellifera, Drosophila melanogaster and Mamestra brassicae after exposure to imidacloprid and amitraz. Hemocytes were exposed to the pesticides in single and co-exposures using zymosan A for immune activation. We measured the effect of these exposures on cell viability, nitric oxide (NO) production from 15 to 120 min and on extracellular hydrogen peroxide (H₂O₂) production after 3 h to assess potential alterations in the oxidative response. Our results indicate that NO and H₂O₂ production is more altered in honeybee hemocytes compared to D. melanogaster and M. brassicae cell lines. There is also a differential production at different time points after pesticide exposure between these insect species as contrasting effects were evident with the oxidative responses in hemocytes. The results imply that imidacloprid and amitraz act differently on the immune response among insect orders and may render honeybee colonies more susceptible to infection and pests.

Four antimicrobial peptides of Asian gypsy moth respond to infection of its viral pathogen, nucleopolyhedrovirus (LdMNPV)

Antimicrobial peptides (AMPs) play essential roles in defending against various invading pathogens. Although antibacterial or antifungal properties of AMPs have been well characterized, the contribution of AMPs to immune defenses against viruses especially baculoviruses is still unclear. In this study, four full-length AMP genes (Ldcec, Ldatt, Ldglo and Ldmor) that encode the cecropin, attacin, gloverin and moricin, respectively, were characterized in Lymantria dispar (Asian gypsy moth). All four AMPs were cationic peptides and exhibited hydrophilicity. Structural analysis showed that the Ldcec and Ldmor were α-helical peptides. Tissue-specific Ldcec expression was the highest in fat body, while expression of Ldatt, Ldglo and Ldmor was the highest in epidermis. All four AMP genes were expressed during all developmental stages with the highest expression in the pupa and adult. Compared to mock infection, expression of these four AMP genes were significantly induced following Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) challenge and sharply increased at 72 h post infection. After Ldglo gene silencing, the DNA replication levels of LdMNPV in L. dispar larvae significantly increased at 48 and 72 h post infection, indicating that the Ldglo could suppress the DNA replication of LdMNPV. Our results suggest that four AMPs of L. dispar may play important roles in antiviral immunity against LdMNPV.

The Role of Mosquito Hemocytes in Viral Infections

Insect hemocytes are the only immune cells that can mount a humoral and cellular immune response. Despite the critical involvement of hemocytes in immune responses against bacteria, fungi, and parasites in mosquitoes, our understanding of their antiviral potential is still limited. It has been shown that hemocytes express humoral factors such as TEP1, PPO, and certain antimicrobial peptides that are known to restrict viral infections. Insect hemocytes also harbor the major immune pathways, such as JAK/STAT, TOLL, IMD, and RNAi, which are critical for the control of viral infection. Recent research has indicated a role for hemocytes in the regulation of viral infection through RNA interference and autophagy; however, the specific mechanism by which this regulation occurs remains uncharacterized. Conversely, some studies have suggested that hemocytes act as agonists of arboviral infection because they lack basal lamina and circulate throughout the whole mosquito, likely facilitating viral dissemination to other tissues such as salivary glands. In addition, hemocytes produce arbovirus agonist factors such as lectins, which enhance viral infection. Here, we summarize our current understanding of hemocytes’ involvement in viral infections.

The immune deficiency and c-Jun N-terminal kinase pathways drive the functional integration of the immune and circulatory systems of mosquitoes

The immune and circulatory systems of animals are functionally integrated. In mammals, the spleen and lymph nodes filter and destroy microbes circulating in the blood and lymph, respectively. In insects, immune cells that surround the heart valves (ostia), called periostial haemocytes, destroy pathogens in the areas of the body that experience the swiftest haemolymph (blood) flow. An infection recruits additional periostial haemocytes, amplifying heart-associated immune responses. Although the structural mechanics of periostial haemocyte aggregation have been defined, the genetic factors that regulate this process remain less understood. Here, we conducted RNA sequencing in the African malaria mosquito, Anopheles gambiae, and discovered that an infection upregulates multiple components of the immune deficiency (IMD) and c-Jun N-terminal kinase (JNK) pathways in the heart with periostial haemocytes. This upregulation is greater in the heart with periostial haemocytes than in the circulating haemocytes or the entire abdomen. RNA interference-based knockdown then showed that the IMD and JNK pathways drive periostial haemocyte aggregation and alter phagocytosis and melanization on the heart, thereby demonstrating that these pathways regulate the functional integration between the immune and circulatory systems. Understanding how insects fight infection lays the foundation for novel strategies that could protect beneficial insects and harm detrimental ones.

Transglutaminase 3 negatively regulates immune responses on the heart of the mosquito, Anopheles gambiae

The immune and circulatory systems of insects are functionally integrated. Following infection, immune cells called hemocytes aggregate around the ostia (valves) of the heart. An earlier RNA sequencing project in the African malaria mosquito, Anopheles gambiae, revealed that the heart-associated hemocytes, called periostial hemocytes, express transglutaminases more highly than hemocytes elsewhere in the body. Here, we further queried the expression of these transglutaminase genes and examined whether they play a role in heart-associated immune responses. We found that, in the whole body, injury upregulates the expression of TGase2, whereas infection upregulates TGase1, TGase2 and TGase3. RNAi-based knockdown of TGase1 and TGase2 did not alter periostial hemocyte aggregation, but knockdown of TGase3 increased the number of periostial hemocytes during the early stages of infection and the sequestration of melanin by periostial hemocytes during the later stages of infection. In uninfected mosquitoes, knockdown of TGase3 also slightly reduced the number of sessile hemocytes outside of the periostial regions. Taken altogether, these data show that TGase3 negatively regulates periostial hemocyte aggregation, and we hypothesize that this occurs by negatively regulating the immune deficiency pathway and by altering hemocyte adhesion. In conclusion, TGase3 is involved in the functional integration between the immune and circulatory systems of mosquitoes.

Diversity of insect antimicrobial peptides and proteins - A functional perspective: A review

The innate immune response of insects provides a robust line of defense against pathogenic microbes and eukaryotic parasites. It consists of two types of overlapping immune responses, named humoral and cellular, which share protective molecules and regulatory mechanisms that closely coordinate to prevent the spread and replication of pathogens within the compromised insect hemocoel. The major feature of the humoral part of the insect immune system involves the production and secretion of antimicrobial peptides from the fat body, which is considered analogous to adipose tissue and liver in vertebrates. Previous research has identified and characterized the nature of antimicrobial peptides that are directed against various targets during the different stages of infection. Here we review this information focusing mostly on the diversity and mode of action of these host defense components, and their critical contribution to maintaining host homeostasis. Extending this knowledge is paramount for understanding the evolution of innate immune function and the physiological balance required to provide sufficient protection to the host against external enemies while avoiding overactivation signaling events that would severely undermine physiological stability.

The Search of a Malaria Vaccine: The Time for Modified Immuno-Potentiating Probes

Malaria is a deadly disease that takes the lives of more than 420,000 people a year and is responsible for more than 229 million clinical cases globally. In 2019, 95% of malaria morbidity occurred in African countries. The development of a highly protective vaccine is an urgent task that remains to be solved. Many vaccine candidates have been developed, from the use of the entire attenuated and irradiated pre-erythrocytic parasite forms (or recombinantly expressed antigens thereof) to synthetic candidates formulated in a variety of adjuvants and delivery systems, however these have unfortunately proven a limited efficacy. At present, some vaccine candidates are finishing safety and protective efficacy trials, such as the PfSPZ and the RTS,S/AS01 which are being introduced in Africa. We propose a strategy for introducing non-natural elements into target antigens representing key epitopes of Plasmodium spp. Accordingly, chemical strategies and knowledge of host immunity to Plasmodium spp. have served as the basis. Evidence is obtained after being tested in experimental rodent models for malaria infection and recognized for human sera from malaria-endemic regions. This encourages us to propose such an immune-potentiating strategy to be further considered in the search for new vaccine candidates.

Lysozyme c-1 gene is overexpressed in Anopheles albimanus pericardial cells after an immune challenge

Different evidences suggest that pericardial cells play an important role during the immune response against pathogens that invade the mosquito hemocoel. Previously, we identified two lysozyme genes in Anopheles albimanus heart transcriptome. The present study showed that one of these genes (ID_VB: AALB004517) has high percentage of identity to mosquito lysozyme genes related to immunity, suggesting its possible participation during the mosquito immune response. This An. albimanus gen, constitutively expressed lysozyme c-1 mRNA (albLys c-1) in mosquito heart; however, it was overexpressed in bacteria-injected mosquitoes. In heart extract samples, we identified a protein of approximately 14 kDa (likely lysozyme c-1), which lysed M. luteus. In addition, mRNA-FISH assay in heart samples, showed specific fluorescent hybridization signal in pericardial cells from M. luteus-injected mosquitos. We conclude that for the first time an inducible immune factor (lysozyme c-1) is identified in Anopheles albimanus mosquito pericardial cells, which could be a key component in the response against pathogens that interact with the mosquito heart.

Nitric oxide produced by periostial hemocytes modulates the bacterial infection-induced reduction of the mosquito heart rate

The circulatory and immune systems of mosquitoes are functionally integrated. An infection induces the migration of hemocytes to the dorsal vessel, and specifically, to the regions surrounding the ostia of the heart. These periostial hemocytes phagocytose pathogens in the areas of the hemocoel that experience the highest hemolymph flow. Here, we investigated whether a bacterial infection affects cardiac rhythmicity in the African malaria mosquito, Anopheles gambiae We discovered that infection with Escherichia coli, Staphylococcus aureus and Staphylococcus epidermidis, but not Micrococcus luteus, reduces the mosquito heart rate and alters the proportional directionality of heart contractions. Infection does not alter the expression of genes encoding crustacean cardioactive peptide (CCAP), FMRFamide, corazonin, neuropeptide F or short neuropeptide F, indicating that they do not drive the cardiac phenotype. Infection upregulates the transcription of two superoxide dismutase (SOD) genes, catalase and a glutathione peroxidase, but dramatically induces upregulation of nitric oxide synthase (NOS) in both the heart and hemocytes. Within the heart, nitric oxide synthase is produced by periostial hemocytes, and chemically inhibiting the production of nitric oxide using l-NAME reverses the infection-induced cardiac phenotype. Finally, infection induces the upregulation of two lysozyme genes in the heart and other tissues, and treating mosquitoes with lysozyme reduces the heart rate in a manner reminiscent of the infection phenotype. These data demonstrate an exciting new facet of the integration between the immune and circulatory systems of insects, whereby a hemocyte-produced factor with immune activity, namely nitric oxide, modulates heart physiology.

Developmental and comparative perspectives on mosquito immunity

Diseases spread by mosquitoes have killed more people than those spread by any other group of arthropod vectors and remain an important factor in determining global health and economic stability. The mosquito innate immune system can act to either modulate infection with human pathogens or fight off entomopathogens and increase the fitness and longevity of infected mosquitoes. While work remains towards understanding the larval immune system and the development of the mosquito immune system, it has recently become clearer that environmental factors heavily shape the developing mosquito immune system and continue to influence the adult immune system as well. The adult immune system has been well-studied and is known to involve multiple tissues and diverse molecular mechanisms. This review summarizes and synthesizes what is currently understood about the development of the mosquito immune system and includes comparisons of immune components unique to mosquitoes among the blood-feeding arthropods as well as important distinguishing factors between the anopheline and culicine mosquitoes. An explanation is included for how mosquito immunity factors into vector competence and vectorial capacity is presented along with a model for the interrelationships between nutrition, microbiome, pathogen interactions and behavior as they relate to mosquito development, immune status, adult female fitness and ultimately, vectorial capacity. Novel discoveries in the fields of mosquito ecoimmunology, neuroimmunology, and intracellular antiviral responses are highlighted.

Transcriptome-wide responses of adult melon thrips (Thrips palmi) associated with capsicum chlorosis virus infection

Thrips palmi is a widely distributed major agricultural pest in the tropics and subtropics, causing significant losses in cucurbit and solanaceous crops through feeding damage and transmission of tospoviruses. Thrips palmi is a vector of capsicum chlorosis virus (CaCV) in Australia. The present understanding of transmission biology and potential effects of CaCV on T. palmi is limited. To gain insights into molecular responses to CaCV infection, we performed RNA-Seq to identify thrips transcripts that are differentially-abundant during virus infection of adults. De-novo assembly of the transcriptome generated from whole bodies of T. palmi adults generated 166,445 contigs, of which ~24% contained a predicted open reading frame. We identified 1,389 differentially-expressed (DE) transcripts, with comparable numbers up- (708) and down-regulated (681) in virus-exposed thrips compared to non-exposed thrips. Approximately 59% of these DE transcripts had significant matches to NCBI non-redundant proteins (Blastx) and Blast2GO identified provisional functional categories among the up-regulated transcripts in virus-exposed thrips including innate immune response-related genes, salivary gland and/or gut-associated genes and vitellogenin genes. The majority of the immune-related proteins are known to serve functions in lysosome activity and melanisation in insects. Most of the up-regulated oral and extra-oral digestion-associated genes appear to be involved in digestion of proteins, lipids and plant cell wall components which may indirectly enhance the likelihood or frequency of virus transmission or may be involved in the regulation of host defence responses. Most of the down-regulated transcripts fell into the gene ontology functional category of 'structural constituent of cuticle'. Comparison to DE genes responsive to tomato spotted wilt virus in Frankliniella occidentalis indicates conservation of some thrips molecular responses to infection by different tospoviruses. This study assembled the first transcriptome in the genus Thrips and provides important data to broaden our understanding of networks of molecular interactions between thrips and tospoviruses.

Allatotropin: A pleiotropic neuropeptide that elicits mosquito immune responses

Allatotropins (AT) are neuropeptides with pleotropic functions on a variety of insect tissues. They affect processes such as juvenile hormone biosynthesis, cardiac rhythm, oviduct and hindgut contractions, nutrient absorption and circadian cycle. The present work provides experimental evidence that AT elicits immune responses in two important mosquito disease vectors, Anopheles albimanus and Aedes aegypti. Hemocytes and an immune-competent mosquito cell line responded to AT by showing strong morphological changes and increasing bacterial phagocytic activity. Phenoloxidase activity in hemolymph was also increased in Ae. aegypti mosquitoes treated with AT but not in An. albimanus, suggesting differences in the AT-dependent immune activation in the two species. In addition, two important insect immune markers, nitric oxide levels and expression of antimicrobial peptide genes, were increased in An. albimanus guts after AT treatment. AT conjugated to quantum dot nanocrystals (QDots) specifically labeled hemocytes in vivo in both mosquito species, implying molecular interactions between AT and hemocytes. The results of our studies suggest a new role for AT in the modulation of the immune response in mosquitoes.

Functional integration of the circulatory, immune, and respiratory systems in mosquito larvae: pathogen killing in the hemocyte-rich tracheal tufts

BACKGROUND

As both larvae and adults, mosquitoes encounter a barrage of immune insults, ranging from microbe-rich communities in larval habitats to ingested blood-borne pathogens in adult blood meals. Given that mosquito adults have evolved an efficient means of eliminating infections in their hemocoel (body cavity) via the coordinated action of their immune and circulatory systems, the goal of the present study was to determine whether such functional integration is also present in larvae.

RESULTS

By fluorescently labeling hemocytes (immune cells), pericardial cells, and the heart, we discovered that fourth instar larvae, unlike adults, contain segmental hemocytes but lack the periostial hemocytes that surround the ostia (heart valves) in abdominal segments 2-7. Instead, larvae contain an abundance of sessile hemocytes at the tracheal tufts, which are respiratory structures that are unique to larvae, are located in the posterior-most abdominal segment, and surround what in larvae are the sole incurrent openings for hemolymph entry into the heart. Injection of fluorescent immune elicitors and bacteria into the larval hemocoel then showed that tracheal tuft hemocytes mount rapid and robust immune responses against foreign insults. Indeed, green fluorescent protein-labeled Escherichia coli flowing with the hemolymph rapidly aggregate exclusively at the tracheal tufts, where they are killed within 24 h post-infection via both phagocytosis and melanization.

CONCLUSION

Together, these findings show that the functional integration of the circulatory, respiratory, and immune systems of mosquitoes varies drastically across life stages.

Limited Specificity in the Injury and Infection Priming against Bacteria in Aedes aegypti Mosquitoes

Injury and infection priming has been observed in several insect groups, reported as host immune protection against contact with a pathogen caused by a previous infection with the same. However, the specific response against a pathogen has not been demonstrated in all insect species. Investigating the specific priming response in insects is important because their immune strategies probably reflect particular selective pressures exerted by different pathogens. Here, we determined whether previous infection of Aedes aegypti would enhance survival and/or lead to greater and specific AMP expression after a second exposure to the same or a distinct bacterium. Mosquitoes previously immunized with a low dose of Escherichia coli, but not Staphylococcus aureus, showed increased survival. Although the host protection herein demonstrated was not specific, each bacterium elicited differential AMP expression. These results can be explained by the susceptible-primed-infected (SPI) epidemiological model, which poses that in the evolution of memory-like responses (priming), a pivotal role is played by pathogen virulence, associated host damage, and the host capacity of pathogen recognition.

Mosquito hemocytes preferentially aggregate and phagocytose pathogens in the periostial regions of the heart that experience the most hemolymph flow

When a mosquito acquires an infection in the hemocoel, dedicated immune cells called hemocytes aggregate around the valves of the heart. These sessile hemocytes are called periostial hemocytes. In the present study we scrutinized the immune response mounted by the periostial hemocytes of the malaria mosquito, Anopheles gambiae, against bacterial pathogens, and tested the relationship between periostial hemocyte aggregation, immune activity, and hemolymph flow. Initially, we quantified the process of periostial hemocyte aggregation and found that hemocytes migrate to the periostial regions in response to infection with Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, and Micrococcus luteus (all infections tested). Then, we investigated whether the periostial hemocytes are evenly distributed along the six periostial regions of the heart, and found that they preferentially aggregate in the periostial regions of the mid-abdominal segments (4, 5 and 6). This distribution perfectly correlates with the spatial distribution of phagocytic activity along the surface of the heart, and to a lesser extent, with the distribution of melanin deposits. Finally, experiments measuring circulatory physiology found that the majority of hemolymph enters the heart through the ostia located in the periostial regions of abdominal segments 4, 5, and 6. These data show that periostial hemocytes aggregate on the surface of the heart in response to diverse foreign stimuli, and that both hemocytes and immune activity preferentially occur in the regions that experience the swiftest hemolymph flow. Thus, these data show that two major organ systems - the immune and circulatory systems - interact to control infections.

Location, morphology and function of nephrocytes in termites

Insect nephrocytes are cells bathed in hemolymph and considered to have an excretory function. These cells have ambiguous nomenclature and are understudied in termites. This study is the first report on the occurrence, morphology and function of nephrocytes in different termite castes. Cytological characteristics in specific developmental stages and castes enable physiological functions to be inferred. Perforate diaphragms indicate a role in filtration, while the extensive peripheral invaginations of the cell membrane suggest active endocytosis. A sequence of morphologies in putative digestive vacuoles infers a lysosomal system and the occurrence of phosphatases suggests a function involving detoxification of substances sequestered from hemolymph. Pericardical nephrocytes took up the dye trypan blue injected in live termites, suggesting their activity connected to the filtration of the hemolymph. Additionally, histochemical tests showed the existence of stored proteins in their cytoplasm. These cells present a well-developed Golgi apparatus and abundant rough endoplasmic reticulum, consistent with protein synthesis. This study highlights the importance of nephrocytes in Isoptera and opens perspectives for further research of these cells.

Development and glycoprotein composition of the perimicrovillar membrane in Triatoma (Meccus) pallidipennis (Hemiptera: Reduviidae)

Hemipterans and thysanopterans (Paneoptera: Condylognatha) differ from other insects by having an intestinal perimicrovillar membrane (PMM) which extends from the base of the microvilli to the intestinal lumen. The development and composition of the PMM in hematophagous Reduviidae depend on factors related to diet. The PMM may also allow the human parasite Trypanosoma cruzi, the etiological agent of human Chagas Disease, to establish and develop in this insect vector. We studied the PMM development in the Mexican vector of Chagas Disease, Triatoma (Meccus) pallidipennis. We describe changes in the midgut epithelial cells of insects in response to starvation, and at different times (10, 15 and 20 days) after bloodfeeding. In starved insects, the midguts showed epithelial cells closely connected to each other but apparently free of PMM with some regions being periodic acid-Schiff (PAS-Schiff) positive. In contrast, the PMM was evident and fully developed in the midgut region of insects 15 days after feeding. After this time, the PMM completely covered the microvilli and reached the midgut lumen. At 15 days following feeding the labeled PAS-Schiff increased in the epithelial apex, suggesting an increase in carbohydrates. Lectins as histochemical reagents show the presence of a variety of glycoconjugates including mannose, glucose, galactosamine, N-acetyl-galactosamine. Also present were N-acetyl-glucosamine and sialic acid which contribute to the successful establishment and replication or T. cruzi in its insect vectors. By means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the formation and structure of the PMM is confirmed at 15 days post feeding. Our results confirmed the importance of the feeding processes in the formation of the PMM and showed the nature of the biochemical composition of the vectors' intestine in this important Mexican vector of Chagas disease.

The ultrastructure of the Aedes aegypti heart

Comparative structural analyses of the heart and associated tissues in 4th instar larvae (L4), pupae and adults of Aedes aegypti were undertaken using a combination of microscopy techniques. The Ae. aegypti heart consists of cardiomyocytes arranged in a helical fashion, and it is physically associated with intersegmental groups of pericardial cells (PCs) and the alary muscles (AMs). Ramifications commonly present in AMs are more developed in adults than in the immature stages. Pericardial cells absorb and store extracellular components as shown by the uptake of carmine dye fed in larval diet. We also observed that carmine stained inclusions corresponding to electron-dense structures resembling lysosomes that were more abundant and prominent in pupae, suggestive of increase of waste accumulation during pupation. The results presented here expand on previously known aspects of the mosquito heart and describe for the first time comparative aspects of the morphology of the heart in different developmental stages.

Spatial and temporal in vivo analysis of circulating and sessile immune cells in mosquitoes: hemocyte mitosis following infection

Background

Mosquitoes respond to infection by mounting immune responses. The primary regulators of these immune responses are cells called hemocytes, which kill pathogens via phagocytosis and via the production of soluble antimicrobial factors. Mosquito hemocytes are circulated throughout the hemocoel (body cavity) by the swift flow of hemolymph (blood), and data show that some hemocytes also exist as sessile cells that are attached to tissues. The purpose of this study was to create a quantitative physical map of hemocyte distribution in the mosquito, Anopheles gambiae, and to describe the cellular immune response in an organismal context.

Results

Using correlative imaging methods we found that the number of hemocytes in a mosquito decreases with age, but that regardless of age, approximately 75% of the hemocytes occur in circulation and 25% occur as sessile cells. Infection induces an increase in the number of hemocytes, and tubulin and nuclear staining showed that this increase is primarily due to mitosis and, more specifically, autonomous cell division, by circulating granulocytes. The majority of sessile hemocytes are present on the abdominal wall, although significant numbers of hemocytes are also present in the thorax, head, and several of the appendages. Within the abdominal wall, the areas of highest hemocyte density are the periostial regions (regions surrounding the valves of the heart, or ostia), which are ideal locations for pathogen capture as these are areas of high hemolymph flow.

Conclusions

These data describe the spatial and temporal distribution of mosquito hemocytes, and map the cellular response to infection throughout the hemocoel.