Immune mechanisms in insects

Lipopolysaccharide-Induced Immunological Tolerance in Monocyte-Derived Dendritic Cells

Bacterial lipopolysaccharides (LPS), also referred to as endotoxins, are major outer surface membrane components present on almost all Gram-negative bacteria and are major determinants of sepsis-related clinical complications including septic shock. LPS acts as a strong stimulator of innate or natural immunity in a wide variety of eukaryotic species ranging from insects to humans including specific effects on the adaptive immune system. However, following immune stimulation, lipopolysaccharide can induce tolerance which is an essential immune-homeostatic response that prevents overactivation of the inflammatory response. The tolerance induced by LPS is a state of reduced immune responsiveness due to persistent and repeated challenges, resulting in decreased expression of pro-inflammatory modulators and up-regulation of antimicrobials and other mediators that promote a reduction of inflammation. The presence of environmental-derived LPS may play a key role in decreasing autoimmune diseases and gut tolerance to the plethora of ingested antigens. The use of LPS may be an important immune adjuvant as demonstrated by the promotion of IDO1 increase when present in the fusion protein complex of CTB-INS (a chimera of the cholera toxin B subunit linked to proinsulin) that inhibits human monocyte-derived DC (moDC) activation, which may act through an IDO1-dependent pathway. The resultant state of DC tolerance can be further enhanced by the presence of residual E. coli lipopolysaccharide (LPS) which is almost always present in partially purified CTB-INS preparations. The approach to using an adjuvant with an autoantigen in immunotherapy promises effective treatment for devastating tissue-specific autoimmune diseases like multiple sclerosis (MS) and type 1 diabetes (T1D).

Hematopoietic plasticity mapped in Drosophila and other insects

Hemocytes, similar to vertebrate blood cells, play important roles in insect development and immunity, but it is not well understood how they perform their tasks. New technology, in particular single-cell transcriptomic analysis in combination with Drosophila genetics, may now change this picture. This review aims to make sense of recently published data, focusing on Drosophila melanogaster and comparing to data from other drosophilids, the malaria mosquito, Anopheles gambiae, and the silkworm, Bombyx mori. Basically, the new data support the presence of a few major classes of hemocytes: (1) a highly heterogenous and plastic class of professional phagocytes with many functions, called plasmatocytes in Drosophila and granular cells in other insects. (2) A conserved class of cells that control melanin deposition around parasites and wounds, called crystal cells in D. melanogaster, and oenocytoids in other insects. (3) A new class of cells, the primocytes, so far only identified in D. melanogaster. They are related to cells of the so-called posterior signaling center of the larval hematopoietic organ, which controls the hematopoiesis of other hemocytes. (4) Different kinds of specialized cells, like the lamellocytes in D. melanogaster, for the encapsulation of parasites. These cells undergo rapid evolution, and the homology relationships between such cells in different insects are uncertain. Lists of genes expressed in the different hemocyte classes now provide a solid ground for further investigation of function.

Novel host immune evasion strategy of the endoparasitoid Drino inconspicuoides

The tachinid fly Drino inconspicuoides (Diptera: Tachinidae) is an ovolarviparous endoparasitoid whose larvae develop in the host haemocoel and avoids the host immune system. In this study, we investigated the immune evasion mechanisms of this species during infestation in the host Mythimna separata (Lepidoptera: Noctuidae). We discovered a unique 'cloak' that surrounded D. inconspicuoides larvae that penetrated into the host and determined through genomic polymerase chain reaction analysis that this structure originated from the host rather than the tachinid. The 'cloak' contained both haemocytes and fat body cells from the host, with the haemocytes assembling around the larvae first and the fat body cells then covering the haemocyte layer, following which the two mixed. Living D. inconspicuoides larvae that were wrapped in the 'cloak' were not melanized whereas encapsulated dead larvae were melanized, suggesting that this structure contributes to the avoidance of host immune reactions.

A parasitological evaluation of edible insects and their role in the transmission of parasitic diseases to humans and animals

From 1 January 2018 came into force Regulation (EU) 2015/2238 of the European Parliament and of the Council of 25 November 2015, introducing the concept of "novel foods", including insects and their parts. One of the most commonly used species of insects are: mealworms (Tenebrio molitor), house crickets (Acheta domesticus), cockroaches (Blattodea) and migratory locusts (Locusta migrans). In this context, the unfathomable issue is the role of edible insects in transmitting parasitic diseases that can cause significant losses in their breeding and may pose a threat to humans and animals. The aim of this study was to identify and evaluate the developmental forms of parasites colonizing edible insects in household farms and pet stores in Central Europe and to determine the potential risk of parasitic infections for humans and animals. The experimental material comprised samples of live insects (imagines) from 300 household farms and pet stores, including 75 mealworm farms, 75 house cricket farms, 75 Madagascar hissing cockroach farms and 75 migrating locust farms. Parasites were detected in 244 (81.33%) out of 300 (100%) examined insect farms. In 206 (68.67%) of the cases, the identified parasites were pathogenic for insects only; in 106 (35.33%) cases, parasites were potentially parasitic for animals; and in 91 (30.33%) cases, parasites were potentially pathogenic for humans. Edible insects are an underestimated reservoir of human and animal parasites. Our research indicates the important role of these insects in the epidemiology of parasites pathogenic to vertebrates. Conducted parasitological examination suggests that edible insects may be the most important parasite vector for domestic insectivorous animals. According to our studies the future research should focus on the need for constant monitoring of studied insect farms for pathogens, thus increasing food and feed safety.

Caterpillars induce jasmonates in flowers and alter plant responses to a second attacker

In nature, herbivorous insects and plant pathogens are generally abundant when plants are flowering. Thus, plants face a diversity of attackers during their reproductive phase. Plant responses to one attacker can interfere with responses to a second attacker, and phytohormones that orchestrate plant reproduction are also involved in resistance to insect and pathogen attack. We quantified phytohormonal responses of flowering plants exposed to single or dual attack and studied resistance mechanisms of plants in the flowering stage. Flowering Brassica nigra were exposed to either a chewing caterpillar, a phloem-feeding aphid or a bacterial pathogen, and plant hormonal responses were compared with dual attack situations. We quantified phytohormones in inflorescences and leaves, and determined the consequences of hormonal changes for components of direct and indirect plant resistance. Caterpillars were the main inducers of jasmonates in inflorescences, and the phytohormonal profile of leaves was not affected by either insect or pathogen attack. Dual attack increased plant resistance to caterpillars, but compromised resistance to aphids. Parasitoid performance was negatively correlated with the performance of their hosts. We conclude that plants prioritize resistance of reproductive tissues over vegetative tissues, and that a chewing herbivore species is the main driver of responses in flowering B. nigra.

The functions of serpin-3, a negative-regulator involved in prophenoloxidase activation and antimicrobial peptides expression of Chinese oak silkworm, Antheraea pernyi

Serpins are a superfamily of proteins engaged in various physiological processes in all kingdoms of life. To date, many striking results have demonstrated serpins are involved in the invertebrate immune system by regulating the proteolytic cascades. However, in most insect species, the immune functions of serpins in response against pathogen invasion remain obscure. In this study, we identified a full-length cDNA sequence of serpin, named serpin-3, from the Chinese oak silkworm Antheraea pernyi. Sequence alignments have indicated that Apserpin-3 might regulate the melanization reaction via inhibiting prophenoloxidases-activating protease(s) in plasma. Furthermore, it was detected to be primarily transcribed within the fat body, epidermis and hemocytes with significant induction following immune-challenge. Further studies have shown that the knockdown of serpin-3 up-regulated the prophenoloxidases cascade stimulated by pathogen in hemolymph, while the addition of recombinant serpin-3 along with the same elicitor led to the suppressed activation of prophenoloxidase. Besides, the injection of dsRNA of serpin-3 caused the elevated expression of antimicrobial peptides. Altogether, we arrived at a conclusion that serpin-3 might act as a negative-regulator in prophenoloxidases activation and inhibit the production of antimicrobial peptides in Antheraea pernyi larvae.

Structural, functional, and evolutionary aspects of galectins in aquatic mollusks: From a sweet tooth to the Trojan horse

Galectins constitute a conserved and widely distributed lectin family characterized by their binding affinity for β-galactosides and a unique binding site sequence motif in the carbohydrate recognition domain (CRD). In spite of their structural conservation, galectins display a remarkable functional diversity, by participating in developmental processes, cell adhesion and motility, regulation of immune homeostasis, and recognition of glycans on the surface of viruses, bacteria and protozoan parasites. In contrast with mammals, and other vertebrate and invertebrate taxa, the identification and characterization of bona fide galectins in aquatic mollusks has been relatively recent. Most of the studies have focused on the identification and domain organization of galectin-like transcripts or proteins in diverse tissues and cell types, including hemocytes, and their expression upon environmental or infectious challenge. Lectins from the eastern oyster Crassostrea virginica, however, have been characterized in their molecular, structural and functional aspects and some notable features have become apparent in the galectin repertoire of aquatic mollusks. These including less diversified galectin repertoires and different domain organizations relative to those observed in vertebrates, carbohydrate specificity for blood group oligosaccharides, and up regulation of galectin expression by infectious challenge, a feature that supports their proposed role(s) in innate immune responses. Although galectins from some aquatic mollusks have been shown to recognize microbial pathogens and parasites and promote their phagocytosis, they can also selectively bind to phytoplankton components, suggesting that they also participate in uptake and intracellular digestion of microalgae. In addition, the experimental evidence suggests that the protozoan parasite Perkinsus marinus has co-evolved with the oyster host to be selectively recognized by the oyster hemocyte galectins over algal food or bacterial pathogens, thereby subverting the oyster's innate immune/feeding recognition mechanisms to gain entry into the host cells.

Parasite killing in malaria non-vector mosquito Anopheles culicifacies species B: implication of nitric oxide synthase upregulation

Background

Anopheles culicifacies, the main vector of human malaria in rural India, is a complex of five sibling species. Despite being phylogenetically related, a naturally selected subgroup species B of this sibling species complex is found to be a poor vector of malaria. We have attempted to understand the differences between vector and non-vector Anopheles culicifacies mosquitoes in terms of transcriptionally activated nitric oxide synthase (AcNOS) physiologies to elucidate the mechanism of refractoriness. Identification of the differences between genes and gene products that may impart refractory phenotype can facilitate development of novel malaria transmission blocking strategies.

Methodology/Principal Findings

We conducted a study on phylogenetically related susceptible (species A) and refractory (species B) sibling species of An. culicifacies mosquitoes to characterize biochemical and molecular differences in AcNOS gene and gene elements and their ability to inhibit oocyst growth. We demonstrate that in species B, AcNOS specific activity and nitrite/nitrates in mid-guts and haemolymph were higher as compared to species A after invasion of the mid-gut by P. vivax at the beginning and during the course of blood feeding. Semiquantitative RT-PCR and real time PCR data of AcNOS concluded that this gene is more abundantly expressed in midgut of species B than in species A and is transcriptionally upregulated post blood meals. Dietary feeding of L-NAME along with blood meals significantly inhibited midgut AcNOS activity leading to an increase in oocyst production in An. culicifacies species B.

Conclusions/Significance

We hypothesize that upregulation of mosquito innate cytotoxicity due to NOS in refractory strain to Plasmodium vivax infection may contribute to natural refractoriness in An. culicifacies mosquito population. This innate capacity of refractory mosquitoes could represent the ancestral function of the mosquito immune system against the parasite and could be utilized to understand the molecular basis of refractoriness in planning effective vector control strategies.

Detection of insect immunity substances (lectins) in the midgut extracts from larvae and adult red palm weevil Rhynchophorus ferrugineus (Olivier) in Al-Ahsa, Saudi Arabia

The hemagglutination activities of midgut (MG) fractions of red palm weevil, Rhynchophorus ferrugineus against mammalian erythrocytes (RBC) from man (ABO), rabbit, horse and sheep were studied. The highest titers were seen with rabbit RBC (p < 0.05) followed by human group B, human group O, horse, human group A, human group AB and sheep, respectively. Insect age and nutritional status significantly influenced the agglutinating activities. Some of the unfed insects were having low activities (p > 0.01) than the well fed insects (p < 0.05). The agglutination activities were linearly correlated with the insect age. The agglutination activities were higher in old insects than the young insects (p < 0.05). Further studies are needed to investigate the lectins in the hemolymph of the red palm weevil, Rhynchophorus ferrugineus beside demonstrating their agglutination activities against the natural entomopathogenes organisms of this economically important insect for use in its biological control.

Immunosuppression by larvae ofMoniliformis moniliformis(Acanthocephala) in their cockroach host (Periplaneta Americana)

The results of 4 different assays for haemocytic immune responsiveness in the cockroach,Periplaneta americana, have shown that the presence of larvae ofMoniliformis moniliformiswithin the haemocoele depresses the insect's immune reactivity. Thus, the proportion of haemocytes that phagocytose fluorescent latex beadsin vivo, the proportion of haemocytes that can be stimulatedin vitroby theβ1,3-glucan, laminarin, to produce phenoloxidase, and the number of haemocytic aggregates producedin vivoin response to zymosan stimulation, are significantly depressed compared with control, unparasitized cockroaches. Also, when cockroaches are injected intra-haemocoelically with hatched oncospheres of the tapeworm,Hymenolepis diminuta, a higher prevalence and intensity of tapeworm larvae are found in insects already parasitized byM. moniliformis. All of these assays show that depression rather than total suppression of the immune response occurs; in the wild, this may be sufficient to ensure that the cockroach does not succumb to unrelated infections during the long developmental period of the parasite.

Determination of nitric oxide metabolites, nitrate and nitrite, in Anopheles culicifacies mosquito midgut and haemolymph by anion exchange high-performance liquid chromatography: plausible mechanism of refractoriness

Background

The diverse physiological and pathological role of nitric oxide in innate immune defenses against many intra and extracellular pathogens, have led to the development of various methods for determining nitric oxide (NO) synthesis. NO metabolites, nitrite (NO₂^-) and nitrate (NO₃^-) are produced by the action of an inducible Anopheles culicifacies NO synthase (AcNOS) in mosquito mid-guts and may be central to anti-parasitic arsenal of these mosquitoes.

Method

While exploring a plausible mechanism of refractoriness based on nitric oxide synthase physiology among the sibling species of An. culicifacies, a sensitive, specific and cost effective high performance liquid chromatography (HPLC) method was developed, which is not influenced by the presence of biogenic amines, for the determination of NO₂^- and NO₃^- from mosquito mid-guts and haemolymph.

Results

This method is based on extraction, efficiency, assay reproducibility and contaminant minimization. It entails de-proteinization by centrifugal ultra filtration through ultracel 3 K filter and analysis by high performance anion exchange liquid chromatography (Sphereclone, 5 μ SAX column) with UV detection at 214 nm. The lower detection limit of the assay procedure is 50 pmoles in all midgut and haemolymph samples. Retention times for NO₂^- and NO₃^- in standards and in mid-gut samples were 3.42 and 4.53 min. respectively. Assay linearity for standards ranged between 50 nM and 1 mM. Recoveries of NO₂^- and NO₃^- from spiked samples (1–100 μM) and from the extracted standards (1–100 μM) were calculated to be 100%. Intra-assay and inter assay variations and relative standard deviations (RSDs) for NO₂^- and NO₃^- in spiked and un-spiked midgut samples were 5.7% or less. Increased levels NO₂^- and NO₃^- in midguts and haemolymph of An. culicifacies sibling species B in comparison to species A reflect towards a mechanism of refractoriness based on AcNOS physiology.

Conclusion

HPLC is a sensitive and accurate technique for identification and quantifying pmole levels of NO metabolites in mosquito midguts and haemolymph samples that can be useful for clinical investigations of NO biochemistry, physiology and pharmacology in various biological samples.

A Galectin of Unique Domain Organization from Hemocytes of the Eastern Oyster (Crassostrea virginica) Is a Receptor for the Protistan Parasite Perkinsus marinus

Invertebrates display effective innate immune responses for defense against microbial infection. However, the protozoan parasite Perkinsus marinus causes Dermo disease in the eastern oyster Crassostrea virginica and is responsible for catastrophic damage to shellfisheries and the estuarine environment in North America. The infection mechanisms remain unclear, but it is likely that, while filter feeding, the healthy oysters ingest P. marinus trophozoites released to the water column by the infected neighboring individuals. Inside oyster hemocytes, trophozoites resist oxidative killing, proliferate, and spread throughout the host. However, the mechanism(s) for parasite entry into the hemocyte are unknown. In this study, we show that oyster hemocytes recognize P. marinus via a novel galectin (C. virginica galectin (CvGal)) of unique structure. The biological roles of galectins have only been partly elucidated, mostly encompassing embryogenesis and indirect roles in innate and adaptive immunity mediated by the binding to endogenous ligands. CvGal recognized a variety of potential microbial pathogens and unicellular algae, and preferentially, Perkinsus spp. trophozoites. Attachment and spreading of hemocytes to foreign surfaces induced localization of CvGal to the cell periphery, its secretion and binding to the plasma membrane. Exposure of hemocytes to Perkinsus spp. trophozoites enhanced this process further, and their phagocytosis could be partially inhibited by pretreatment of the hemocytes with anti-CvGal Abs. The evidence presented indicates that CvGal facilitates recognition of selected microbes and algae, thereby promoting phagocytosis of both potential infectious challenges and phytoplankton components, and that P. marinus subverts the host's immune/feeding recognition mechanism to passively gain entry into the hemocytes.

Immunohistochemical examination of PDGF-AB, TGF-beta and their receptors in the hemocytes of a tick, Ornithodoros moubata (Acari: Argasidae)

Growth factors, Platelet Derived Growth Factor (PDGF) and Transforming Growth Factor (TGF)-beta, were demonstrated in vertebrate and invertebrate immmunocytes. It is generally known that the growth factors are important in various biological processes, such as the regulation of cell differentiation, development and wound healing. In the present study, the presence of TGF-beta1 and PDGF-receptor-alpha in plasmatocytes and PDGF-AB in granulocytes of a soft tick, Ornithodoros moubata, was confirmed immunohistochemically. The tick midgut might be damaged by intracellular digestion and penetration of protozoa. Therefore, it is considered that PDGF from granulocytes may affect the PDGF-receptor-alpha in plasmatocytes and TGF-beta from plasmatocytes may function to repair the midgut. The results obtained here add to the elucidation of the functions of tick hemocytes.

Immune responses of the argasid tick Ornithodoros moubata moubata induced by infection with the filarial worm Acanthocheilonema viteae

Investigations were undertaken to determine whether the tick Ornithodoros moubatamoubata mounted a detectable immune response to primary and secondary infections with Acanthocheilonema viteae. Uninfected control tick survival rate was 70%, but only 45% in the primary infection group. Post-secondary infection survival rate (82%) was comparable to controls, indicating that these selected ticks had some protective advantage. Mean A. viteae infective larvae recovery from ticks with secondary infections was 31.4% lower than expected, suggesting the development of immunity. SDS–PAGE of haemolymph for proteins induced post-primary infection yielded a stronger signal at 45 kDa than controls, which was further elevated post-secondary infection. Proteins at 48, 22 and 16 to 18 kDa were detected in haemolymph from infected ticks but not seen from controls. The direct effect of haemolymph on microfilarial viability was examined using a novel in vitro assay; in these preliminary trials no differences were observed in parasite viability when exposed to haemolymph from infected or uninfected groups of ticks.

Induction of cysteine proteinase in the encapsulation of Hymenolepis diminuta eggs in the American cockroach, Periplaneta americana

Haemocytes play an essential role in defending invertebrates against pathogens and parasites that enter their haemocoel. In the present study, the cockroach, Periplaneta americana was able to encapsulate Hymenolepis diminuta eggs within 24 h after injection. Proteolytic activity of egg capsules was determined by gelatin zymography. A gelatinase-type proteolytic enzyme with molecular weight about 65 kDa was present at the time of capsule formation. Enzyme activity was obviously inhibited by leupeptin but not by ethylenediamine tetraacetic acid (EDTA) or 1,10-phenanthroline or phenylmethanesulfonyl fluoride (PMSF). Hence, we tentatively characterized this enzyme as a cysteine proteinase. The specificity of the cellular immune response in vivo and the increased cysteine proteinase activity coincided with the capsule size and encapsulation process. The possible function of this cysteine proteinase activity during encapsulation of the H. diminuta eggs by P. americana is discussed.

Interaction between non-specific electrostatic forces and humoral factors in haemocyte attachment and encapsulation in the edible cockle, Cerastoderma edule

In invertebrates, encapsulation is the common immune defence reaction towards foreign bodies, including multicellular parasites, which enter the haemocoel and are too large to be phagocytosed. This immune response has been most extensively studied in insects, in which it is highly complex, involving a diversity of cellular and molecular processes, but little is known of this process in bivalve molluscs. Non-specific physicochemical properties are known to influence parasite-haemocyte interactions in many invertebrates, and these may provide the common basis of encapsulation on which highly specific biochemical interactions are imposed. The present study uses synthetic beads and thread to mimic inactive metacercarial cysts of trematodes, and thus investigates factors involved in the basic, non-specific mechanisms of cell attachment and encapsulation in the edible cockle, Cerastoderma edule. Results showed that positively charged targets stimulated the most vigorous response, and further detailed experiments revealed that non-specific electrostatic forces and humoral plasma factors have a synergistic role in haemocyte attachment and the encapsulation response of C. edule.

Arbovirus-mosquito interactions and vector specificity

Mosquito-borne arboviruses cause important and expanding disease problems. In this article, Colin Leake reviews the increasing knowledge of the complex interaction of arboviruses with their mosquito vectors and mosquito cells, in vitro, and considers the factors influencing vector specificity and vector competence.

Critical stages in the development of Plasmodium in mosquitoes

One tool for the control of malaria that may become available to future generations of public health workers is the introduction of genes into the Anopheline vector populations that will render the mosquitoes refractory to Plasmodium. Insights from basic research that could transform this idea into a technical reality are presently lacking. In this review, Alon Warburg and Louis Miller focus on one crucial area of research: the identification of potentially vulnerable points in the developmental cycle of Plasmodium in mosquitoes.

TICKCIDAL EFFECT OF MONOCLONAL ANTIBODIES AGAINST HEMOCYTES, OM21, IN AN ADULT FEMALE TICK, ORNITHODOROS MOUBATA (ACARI: ARGASIDAE)

In the present study, monoclonal antibodies (mAbs) against adult Ornithodoros moubata hemocytes were established. Afterward, artificial feeding was performed to assess the tickcidal effect of fetal bovine serum meal containing each mAb. As a result, Om21 showed the strongest tickcidal effect on adult female O. moubata. The reactivity of various tick cells and organs, including the hemocyte, midgut, trachea, ovary, fat body, and muscle, to Om21 was then examined by an indirect immunofluorescent antibody test and by immunoelectron microscopy. Om21 reacted with not only hemocytes but also with fat body cells, epidermis, cuticle of the trachea, connective tissue of the muscle, and the basement membrane of the midgut, trachea, fat body, oocyte, and epidermis. These results suggest that Om21 passing through the midgut epithelium induced a tickcidal effect on hemocytes or various organs. However, the target of Om21 could not be identified in the present study. The antihemocyte mAb produced in this study, Om21, may be useful for the immunological control of ticks.

Association of reticular cells with CD34+/Sca-1+ apoptotic cells in the hemopoietic organ of grasshopper, Euprepocnemis shirakii

Hemopoiesis in orthopteran insects occurs in a hemopoietic organ that is located bilaterally along the aorta. This organ is also known as a reticulo-hemopoietic organ because of the rich presence of reticular cells. This study was performed to further elucidate hemopoiesis in the reticulo-hemopoietic organ of an orthopteran, Euprepocnemis shirakii. We focused on the question why reticular cells are so abundant (35% of cells in hemopoietic organ). Interestingly, 21% of these reticular cells surrounded hemocytes with their reticular cytoplasm. The surrounded hemocytes were distinguished by their different size and darkly stained nucleus. These cells were characterized by immunostaining using antibodies against several types of hemocytes: 45% of the surrounded hemocytes were CD34+, and these positive cells were double stained (over 85%) when immunostained by another hemopoietic pluripotent cell marker, Sca-1. Transmission electron microscopic analysis showed that reticular cells surrounded hemocytes containing large nuclei and poorly developed cytoplasmic organelles. This strongly suggests that the reticular cells surround hemopoietic stem cells. Additionally, surrounded hemopoietic progenitor cells are undergoing apoptosis as indicated by the TUNEL assay. The enclosed apoptotic cells are engulfed and then phagocytosed by reticular cells. Our results suggest that reticular cells are related to the differentiation and apoptosis of hemopoietic stem cells.

Development, characterization, and lethal effect of monoclonal antibodies against hemocytes in an adult female tick, Ornithodoros moubata (Acari: Argasidae)

In the present study, 19 monoclonal antibodies (mAbs) against adult Ornithodoros moubata hemocytes were established, and the reactivity of the hemocytes to these mAbs was examined by an indirect fluorescent antibody test (IFAT), Western blot and immunoprecipitation analyses. It was shown that the reactivities of the hemocytes to the mAbs varied among morphologically similar hemocyte types, and most mAbs produced in the present study showed the multiple band reactivity. However, the presence of shared epitopes among peptide subunits of the same protein or entirely different proteins are not common, so their reactivity could not be explained in detail. These results suggest that there are morphologically similar but functionally differentiated hemocytes. Therefore, in addition to morphological classification, the molecular-based classification of the hemocytes is also required. In order to assess the lethal effect of blood meal containing each mAb, artificial feeding was performed. The OmHC 31 showed the strongest lethal effect on adult female O. moubata. In conclusion, anti-hemocyte mAbs produced in this study are useful not only for the immunological classification of hemocytes but also for the immunological control of the tick.

Classification of larval circulating hemocytes of the silkworm, Bombyx mori, by acridine orange and propidium iodide staining

Circulating hemocytes of the silkworm can be classified by fluorescence microscopy following staining with acridine orange and propidium iodide. Based on their fluorescence characteristics, three groups of circulating hemocytes can be distinguished. The first group, granulocytes and spherulocytes, is positive for acridine orange and contain bright green fluorescent granules when observed by fluorescence microscopy. In granulocytes, these green granules are heterogeneous and relatively small. In contrast, in spherulocytes, the green granules appear more homogenous and larger. The second group of hemocytes consists of prohemocytes and plasmatocytes. These cells appear faint green following staining with acridine orange and do not contain any green fluorescent granules in the cytoplasm. Prohemocytes are round, and their nuclei are dark and clear within a background of faint green fluorescence. Inside the nucleus there are one or two small bright green fluorescent bodies. Plasmatocytes are irregularly shaped and their nuclei are invisible. Oenocytoids belong to the third group, and their nuclei are positive for propidium iodide. Therefore, all five types of circulating hemocytes of the silkworm, including many peculiar ones that are difficult to identify by light microscopy, can now be easily classified by fluorescence microscopy following staining with acridine orange and propidium iodide. In addition, we show that hemocytes positive for acridine orange and propidium iodide are in fact living cells based on assays for hemocyte composition, phagocytosis, and mitochondrial enzyme activity.

Quantitative trait loci in Anopheles gambiae controlling the encapsulation response against Plasmodium cynomolgi Ceylon

Background

Anopheles gambiae females are the world's most successful vectors of human malaria. However, a fraction of these mosquitoes is refractory to Plasmodium development. L3-5, a laboratory selected refractory strain, encapsulates transforming ookinetes/early oocysts of a wide variety of Plasmodium species. Previous studies on these mosquitoes showed that one major (Pen1) and two minor (Pen2, Pen3) autosomal dominant quantitative trait loci (QTLs) control the melanotic encapsulation response against P. cynomolgi B, a simian malaria originating in Malaysia.

Results

We have investigated the response of L3-5 to infection with P. cynomolgi Ceylon, a different but related parasite species, in crosses with the susceptible strain 4Arr. Refractoriness to this parasite is incompletely recessive. Infection and genotyping of F2 intercross females at genome-spanning microsatellite loci revealed that 3 autosomal QTLs control encapsulation of this species. Two loci map to the regions containing Pen2 and Pen3. The novel QTL maps to chromosome 3R, probably to polytene division 32 or 33. Thus the relative contribution of any QTL to oocyst encapsulation varies with the species of parasite. Further, different QTLs were most readily identified in different F2 families. This, like the F1 data, suggests that L3-5 is not genetically homogeneous and that somewhat different pathways may be used to achieve an encapsulation response.

Conclusion

We have shown here that different QTLs are involved in responses against different Plasmodium parasites.

Costs of resistance in insect-parasite and insect-parasitoid interactions

Most, if not all, organisms face attack by natural enemies and will be selected to evolve some form of defence. Resistance may have costs as well as its obvious benefits. These costs may be associated with actual defence or with the maintenance of the defensive machinery irrespective of whether a challenge occurs. In this paper, the evidence for costs of resistance in insect-parasite and insect-parasitoid systems is reviewed, with emphasis on two host-parasitoid systems, based on Drosophila melanogaster and pea aphids as hosts. Data from true insect-parasite systems mainly concern the costs of actual defence; evidence for the costs of standing defences is mostly circumstantial. In pea aphids, the costs of standing defences have so far proved elusive. Resistance amongst clones is not correlated with life-time fecundity, whether measured on good or poor quality plants. Successful defence by a D. melanogaster larva results in a reduction in adult size and fecundity and an increased susceptibility to pupal parasitoids. Costs of standing defences are a reduction in larval competitive ability though these costs only become important when food is limited. It is concluded that costs of resistance can play a pivotal role in the evolutionary and population dynamic interactions between hosts and their parasites.

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.

Plasmatocytes from the moth Pseudoplusia includens induce apoptosis of granular cells

The primary immune response toward internal parasites and other large foreign objects that enter the insect hemocoel is encapsulation. Prior studies indicated that granular cells and plasmatocytes are the two hemocyte types required for capsule formation by the moth Pseudoplusia includens (Lepidoptera: Noctuidae). Capsules formed by P. includens also have a defined architecture with primarily granular cells attaching directly to the target, multiple layers of plasmatocytes adhering to this inner layer of granular cells, and a monolayer of granular cells attaching to the capsule periphery. Dye-exclusion assays indicated that granular cells die shortly after attaching to the capsule periphery, leaving a basal lamina-like layer around the capsule. In examining the mechanisms underlying granular cell death, we found that culture medium preconditioned by plasmatocytes induced apoptosis of granular cells. Characteristics of plasmatocyte-induced apoptosis included condensation of chromatin, cell surface blebbing and fragmentation of nuclear DNA. Plasmatocyte-conditioned medium did not induce apoptosis of other hemocyte types, and medium conditioned by other hemocyte types did not induce apoptosis of granular cells. The adhesive state of granular cells and plasmatocytes also affected levels of apoptosis. Conditioned medium from spread plasmatocytes induced higher levels of granular cell apoptosis than medium conditioned by unspread plasmatocytes. Reciprocally, spread granular cells underwent significantly higher rates of apoptosis than unspread granular cells in medium conditioned by spread plasmatocytes. In situ analysis indicated that granular cells on the periphery of capsules also undergo apoptosis. Collectively, our results suggest that spread plasmatocytes release one or more factors that induce apoptosis of granular cells, and that this response is important in the final phases of capsule formation.

Role of habitat components on the dynamics of Aedes albopictus (Diptera: Culicidae) from New Orleans

Monthly sampling of tire pile populations of Aedes albopictus (Skuse) in Orleans Parish, New Orleans, LA, was done in 1995 to determine prevalence of ascogregarine parasites and changes in wing length. Prevalence of Ascogregarina taiwanensis (Lien & Levine) infection was 100% in midsummer and decreased in the fall and spring (60-70%). Wing lengths were longest in the spring and fall and shortest in midsummer. We evaluated the effect of A. taiwanensis infections under high and deficient levels of leaf litter nutrients on mortality, development time, wing length, and reproductive potential of a New Orleans strain of Ae. albopictus. Parasitism and deficient nutrients caused a 35% increase in the rate of larval mortality and significantly extended the development time of females. Parasitized adults were 5% smaller and produced 23% fewer eggs than unparasitized siblings. In addition, abnormal Malpighian tubule morphology and melanization of ascogregarines were seen in adults from nutrient-deficient microcosms. We conclude that ascogregarine infections affect the dynamics of Ae. albopictus by increasing the mortality of immature stages when nutrients supplies are scarce, and by decreasing the reproductive capacity of females under high nutrient conditions.

Insect immunity: molecular cloning, expression, and characterization of cDNAs and genomic DNA encoding three isoforms of insect defensin in Aedes aegypti

Aedes aegypti were immune activated by injection with bacteria, and the expression of insect defensins was measured over time. Northern analyses indicated that defensin transcriptional activity continued for at least 21 days after bacterial injection, and up to 10 days after saline inoculation. Mature defensin levels in the haemolymph reached approximately 45 microM at 24 h post inoculation. cDNAs encoding the preprodefensins of three previously described mature Ae. aegypti defensins were amplified by PCR, cloned and sequenced. Genomic clones were amplified using primers designed against the cDNA sequence. Sequence comparison indicates that there is significant inter- and intra-isoform variability in the signal peptide and prodefensin sequences of defensin genes. Preprodefensin sequences of isoforms A and B are very similar, consisting of a signal peptide region of twenty amino acids, a prodefensin region of thirty-eight amino acids and a forty amino acid mature peptide domain. The sequence encoding isoform C is significantly different, comprising a signal peptide region of twenty-three amino acids, a prodefensin region of thirty-six amino acids, and the mature protein domain of forty amino acids. Analysis of the genomic clones of each isoform revealed one intron spatially conserved in the prodefensin region of all sequences. The intron in isoforms A and B is 64 nt long, and except for a 4 nt substitution in one clone, these intron sequences are identical. The intron in isoform C is 76 nt long and does not share significant identity with the intron sequences of isoforms A or B. The defensin gene mapped to chromosome 3, between two known loci, blt and LF168.

The role of surface characteristics in eliciting humoral encapsulation of foreign bodies in Plasmodium-refractory and -susceptible strains of Anopheles gambiae

A refractory strain of the mosquito, Anopheles gambiae, melanotically encapsulates and kills many species of malaria parasites, whereas susceptible strains allow the parasites to develop normally. To study the role of surface characteristics in eliciting this immune response, 27 types of chromatography beads that differed in matrix type, charge, functional group, and functional group density were assayed for degree of melanotic encapsulation in refractory and susceptible mosquitoes. Overall, two glucan-based matrices, Sephadex (dextran) and cellulose, stimulated the strongest responses, regardless of functional group. Substituting matrix hydroxyl groups with functional groups on Sephadex and cellulose beads decreased the level of encapsulation. These results demonstrate that glucans induce melanotic encapsulation in An. gambiae. Beads with agarose, polystyrene, and acrylic matrices, and most methacrylate-based beads elicited little or no melanization; however, epoxide-methacrylate beads were encapsulated, demonstrating that glucans are not essential for eliciting a response. Comparisons between the two strains demonstrated that refractory mosquitoes melanized many bead types to a greater degree than did susceptible mosquitoes. On this basis, we propose that an important difference between the two strains is that one of the enzymes involved in the melanization pathway functions at a higher level in the refractory strain. Finally, of all beads tested, only 85% substituted CM-Sephadex beads were virtually unmelanized in susceptible mosquitoes but highly melanized in the refractory strain; thus, a specific surface microenvironment is necessary to demonstrate this effect.

The coevolution of host resistance and parasitoid virulence

Host-parasitoid interactions are abundant in nature and offer great scope for the study of coevolution. A particularly fertile area is the interaction between internal feeding parasitoids and their hosts. Hosts have evolved a variety of means of combating parasitoids, in particular cellular encapsulation, while parasitoids have evolved a wide range of countermeasures. Studies of the evolution of host resistance and parasitoid virulence are reviewed, with an emphasis on work involving Drosophila and its parasitoids. Genetic variation in both traits has been demonstrated using isofemale line and artificial selection techniques. Recent studies have investigated the fitness costs of maintaining the ability to resist parasitoids, the comparative fitness of flies that have successfully defended themselves against parasitoids, and the degree to which resistance and virulence act against one or more species of host or parasitoid. A number of studies have examined geographical patterns, and sought to look for local adaptation; or have compared the traits across a range of species. Finally, the physiological and genetic basis of change in resistance and virulence is being investigated. While concentrating on Drosophila, the limited amount of work on different systems is reviewed, and other possible areas of coevolution in host-parasitoid interactions are briefly discussed.

[Review of the biologic and diagnostic aspects of Trypanosoma (Herpetosoma) rangeli]

This review has three objectives: a) To stimulate further research of this prevalent human infection b) to examine the progress of current diagnostic techniques and c) to emphasise the significance of the flagellate parasite Trypanosoma (Herpetosoma) rangeli in Chagas' Disease endemic areas of South and Central America. Both Trypanosoma rangeli and Trypanosoma cruzi overlap in many of the areas of Latin America utilising the same triatomine vectors. Also a vast range of mammalian species have been found naturally infected with T. rangeli. The biology of the parasitism of T. rangeli is revised and emphasis is given regarding its biological cycle. T. cruzi and T. rangeli share common antigens and cross react serologically. Human infection in the chronic phase may be misdiagnosed as T. cruzi infection. Conventional and modern diagnostic and identification methods are discussed. Unfortunately we do not know the real distribution of T. rangeli infections in most areas and epidemiological studies to examine concomitant dual infections deserve further investigation.

Plasmodium activates the innate immune response of Anopheles gambiae mosquitoes

Innate immune-related gene expression in the major disease vector mosquito Anopheles gambiae has been analyzed following infection by the malaria parasite, Plasmodium berghei. Substantially increased levels of mRNAs encoding the antibacterial peptide defensin and a putative Gram-negative bacteria-binding protein (GNBP) are observed 20-30 h after ingestion of an infected blood-meal, at a time which indicates that this induction is a response to parasite invasion of the midgut epithelium. The induction is dependent upon the ingestion of infective, sexual-stage parasites, and is not due to opportunistic co-penetration of resident gut micro-organisms into the hemocoel. The response is activated following infection both locally (in the midgut) and systemically (in remaining tissues, presumably fat body and/or hemocytes). The observation that Plasmodium can trigger a molecularly defined immune response in the vector constitutes an important advance in our understanding of parasite-vector interactions that are potentially involved in malaria transmission, and extends knowledge of the innate immune system of insects to encompass responses to protozoan parasites.

Drosophila cellular immunity against parasitoids

Insect host-parasite interrelations involve co-adaptations of considerable complexity. Against endoparasites, immune competent insect hosts initiate a hemocyte-mediated response that quickly destroys the intruders and envelops them in multilayered, melanotic capsules. In this review, Yves Carton and Anthony Nappi focus on recent studies of the cytological, biochemical and genetic mechanisms involved in the cellular immune response of Drosophila against wasp parasitoids.

Inducible immune factors of the vector mosquito Anopheles gambiae: biochemical purification of a defensin antibacterial peptide and molecular cloning of preprodefensin cDNA

Larvae of the mosquito vector of human malaria, Anopheles gambiae, were inoculated with bacteria and extracts were biochemically fractionated by reverse-phase HPLC. Multiple induced polypeptides and antibacterial activities were observed following bacterial infection, including a member of the insect defensin family of antibacterial proteins. A cDNA encoding An. gambiae preprodefensin was isolated using PCR primers based on phylogenetically conserved sequences. The mature peptide is highly conserved, but the signal and propeptide segments are not, relative to corresponding defensin sequences of other insects. Defensin expression is induced in response to bacterial infection, in both adult and larval stages. In contrast, pupae express defensin mRNA constitutively. Defensin expression may prove a valuable molecular marker to monitor the An. gambiae host response to infection by parasitic protozoa of medical importance.

Differential induction of antibacterial transcripts in Drosophila susceptible and resistant to parasitism by Leptopilina boulardi

Two well-described elements of the immune response of insects include encapsulation of metazoan parasites (blood-cell-mediated) and the production of antibacterial peptides (humoral and/or cellular). However, the possible functional interrelationship between cellular encapsulation and antibacterial responses, and the extent to which the two components may be co-regulated, are poorly understood. We used a novel approach involving strains of Drosophila resistant (R) or susceptible (S) to the wasp parasitoid Leptopilina boulardi to study the expression of three genes involved in the antibacterial response: Dorsal-related immunity factor (Dif), Cecropin (CecA1) and Diptericin (Dip). Both S and R strains produced high levels of all antibacterial transcripts upon bacterial injection. However, when parasitized the R strain showed no induction whilst the S strain did. This lack of antibacterial transcript induction in the parasitized R strain not only clarifies the separation of these two types of immune response but also raises the fascinating possibility of a link in their genetic regulation.

Immunity to eukaryotic parasites in vector insects

Mosquitoes and blackflies have been the focus of recent efforts to elucidate factors influencing the susceptibility of vector insects to metazoan and protozoan parasites of medical significance. Vector species exhibit variation in cellular and humoral immune responses, as highlighted by studies of melanotic encapsulation and components of the phenoloxidase system. Significant progress has been made in the development of genetic maps based upon molecular markers, leading to the genetic analysis of loci influencing susceptibility. The identification of specific inducible antibacterial peptides, and the cloning of genes encoding immune effector proteins as well as potential regulatory factors, open the path to fruitful studies of vector insect innate immunity and its relationship to insect-parasite interactions.

Prophenoloxidase system activation in the crayfish Procambarus clarki

The prophenoloxidase system (proPO) was studied in primary cultures of hemocytes of the crayfish Procambarus clarki. Both zymosan and lipopolysaccharide (LPS) separately induced rapid degranulation and lysis of semigranular hemocytes, with concurrent release of proPO. ProPO could be demonstrated in the hemocyte lysate supernatant (HLS) obtained by a freeze/thaw method, and was specifically activated by LPS and zymosan. Phenoloxidase activity was blocked by serine protease inhibitors, such as soybean trypsin inhibitor (STI), leupeptin, and phenylmethyl-sulphonylfluoride (PMSF), and substantially increased by cysteine protease inhibitors (N-methylmaleimide, N-ethylmaleimide, and iodoacetamide). This enhancement was observed only when the proPO system was activated. Incubation without activators or preincubation with STI prevented the induced enhancement. Electrophoretic analyses of HLS treated with zymosan or LPS showed that three bands at 41, 39, and 37 kDa were specifically modified when the system was activated. These results suggest that a serine protease is involved in the activation of the proPO system in P. clarki, and a mechanism susceptible to cysteine protease inhibitors could be related to its regulation.

Echinostoma paraensei and Schistosoma mansoni: adherence of unaltered or modified latex beads to hemocytes of the host snail Biomphalaria glabrata

Hemocytes derived from a strain (13-16-R1) of Biomphalaria glabrata resistant to Schistosoma mansoni were significantly more likely to bind untreated latex beads than hemocytes from the schistosome-susceptible M line strain. Beads preincubated in 13-16-R1 plasma were more readily bound by both 13-16-R1 and M line hemocytes than beads preincubated in M line plasma. Beads preincubated in plasma derived from snails of either strain infected with the trematode Echinostoma paraensei were more readily bound by hemocytes than beads preincubated in plasma from control snails of the corresponding strain. Plasma from snails exposed to S. mansoni did not have a similar effect. Throughout these experiments, beads receiving a particular treatment were consistently bound at higher rates by 13-16-R1 than M line hemocytes. SDS-PAGE of plasma components eluted from beads revealed differences between treatments, particularly in diffuse bands falling into two groups, of 75-130 and 150-220 kDa. The results indicate that both hemocytes and plasma components from the two host strains differ and identify plasma molecules deserving of additional study as possible modulators of hemocyte effector functions. Also, S. mansoni and E. paraensei provoked different responses in the same host snail.

Cecropia immunoresponsive factor, an insect immunoresponsive factor with DNA-binding properties similar to nuclear-factor kappa B

The immune genes in Hyalophora cecropia contain an upstream sequence that is homologous to the binding site of the mammalian nuclear-factor kappa B (NF-kappa B). These genes are strongly induced by bacteria, lipopolysaccharides and 4 beta-phorbol 12-myristate 13-acetate. Induction of the immune genes involves the activation of a DNA-binding protein complex that we have named Cecropia immunoresponsive factor (CIF). CIF specifically recognizes the kappa B-like DNA sequences in the promoter regions of the Cecropia immune genes. The DNA binding activity of CIF correlates well with the transcriptional induction of the immune genes. Competition assays show that CIF has a DNA binding specificity similar to mammalian NF-kappa B. The two factors also share other characteristics, including the pattern of induction and the migration on the native gel.

Induction of antibacterial activity in the haemolymph of the silkworm, Bombyx mori, by injection of formalin-treated Escherichia coli K-12 in the anterior and posterior body part of the ligated larvae

1. Induction of antibacterial activity was investigated in the ligated fifth instar larvae of the silkworm, Bombyx mori, by injection of formalin-treated Escherichia coli K-12 into the haemocoel in the anterior and in the posterior body part, followed by activity determination by inhibition zone assay of the haemolymph at 12 and 24 hr after immunization. 2. At 12 hr after immunization, high antibacterial activity, approximately 6.8-7.5 mm in the anterior body part and 4.5-6.4 mm in the posterior body part in diameter of a clear zone (2.0 mm for no activity) was detectable in day 3 larvae. This result was in good contrast to expression of lectin gene in the ligated flesh fly, Sarcophaga peregrena (Shiraishi and Natori, 1988, FEBS Lett. 232, 163-166), in which only the anterior part of insect responded to stimulus of injury. 3. Antibacterial activity at 24 hr after immunization in days 3 or 4 ligated larvae was lower than that at 12 hr; 4.0-4.5 mm of activity was observed in the anterior body part, and no activity was observed in day 3 ligated larvae in the posterior body part. 4. Acid polyacrylamide gel electrophoresis of the haemolymph of immunized insects followed by overlay assay showed that the size of antibacterial activity bands were similar between the haemolymph from 12 hr and from 24 hr, and between the anterior and the posterior body part. This result was contradictory to the observation of activity by inhibition zone assay. The activity bands were associated with peptides that were similar to cecropin-like peptides A and B in the silkworm.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibacterial activity inducible in the haemolymph of the silkworm, Bombyx mori, by injection of formalin-treated Escherichia coli K-12 during the fifth larval instar and pharate adult development

1. Antibacterial activity inducible in the haemolymph of the silkworm, Bombyx mori, by immunization, i.e. by injection of formalin-treated Escherichia coli (E. coli) K-12 during the fifth larval instar and pharate adult development that was reared aseptically on an artificial diet was determined by inhibition zone assay using the same bacterium as a test organism. 2. A peak of antibacterial activity was observed in each development stage; approximately 8 mm in diameter of a clear zone at days 3 or 4 in the fifth larval instar and approximately 5 mm at day 1 in the pharate adults. 3. Acid polyacrylamide gel electrophoresis of immunized haemolymph followed by overlay assay showed that an activity band was associated with two peptide bands that were similar to the cecropin-like peptides A and B that were reported in the silkworm (Morishima et al., 1988, Agri. Biol. Chem. 52, 929-934). Any other activity bands were not observed. No activity band was detectable from the haemolymph of non-immunized insects. 4. Fractionation of antibacterial peptides in immunized haemolymph on a CM-cellulose column resulted in separation of two groups of activity, both in the fifth instar larvae and in the pharate adults with a slight difference in elution conditions. 5. Duration of high antibacterial activity induced by a single immunization was approximately 12 hr in the fifth instar day 3 larvae and 48 hr in the day 2 pharate adults.

Localization of juvenile hormone esterase during development in normal and in recombinant baculovirus-infected larvae of the moth Trichoplusia ni

The pathogenesis and cellular localization of juvenile hormone esterase (JHE) was examined in larvae of the moth Trichoplusia ni, infected with a recombinant baculovirus (Autographa californica nuclear polyhedrosis virus: AcNPV) engineered to produce high levels of JHE (JHE virus). The course of JHE localization in the recombinant virus infected larvae was compared with that of both wild type AcNPV infected, and uninfected larvae, using immunogold electron microscopy. In the JHE virus infected insects, high levels of JHE were observed in the endoplasmic reticulum of all cells showing evidence of viral structures in the nucleus, except for gut cells which showed only background JHE levels. Tracheole cells and haemocytes appeared to play a role in the dissemination of infection. In uninfected larvae, fat body and epidermis were the major tissues staining for JHE, which was only detectable at peak times of JHE activity during the fifth instar: lower levels at other times could not be distinguished from background. JHE was also present in lysosomes of granular haemocytes: these lysosomes increased in number in the fifth instar compared to the fourth instar. Similar lysosome-like granules in the pericardial cells did not become highly positive for JHE antigen until the fifth instar.

Insect antibacterial proteins: not just for insects and against bacteria

In response to a bacterial infection, insects launch an array of countermeasures. Among these are the antibacterial proteins, which effectively lyse bacteria or are bacteriostatic. These proteins were generally assumed to be restricted to insects, yet recent information has shown some homologous counterparts in vertebrates, including humans. Recent data have revealed that at least some of these proteins can also act against eukaryotic cells, including human infectious parasites. The latter activities have opened up new possibilities for disease control.

Mosquito host influences on development of filariae

A brief review is presented of the literature relating to factors which limit the capacity of filariae to develop in mosquitoes, with particular emphasis on immune mechanisms. Most insects respond to bacterial infection by the production of potent antibacterial proteins, but little is known of this aspect of the immune response in mosquitoes or of the possible influence of immune proteins on the fate of filarial infections in mosquitoes. A summary account is given of recent experiments with the mosquito Aedes aegypti which involve passive transfer of immune haemolymph together with its in vitro assay and SDS-PAGE examination for induced proteins. These experiments demonstrate the production, in response to inoculation with Brugia pahangi, Escherichia coli, and various components of microbial cell walls, of haemolymph factors which are protective against filarial infection. It remains to be seen whether mosquitoes can produce a specific protective response to infection with eukaryotic organisms such as filaria that is distinctive from that mobilized against bacteria.