Microplitis demolitor bracovirus inhibits phagocytosis by hemocytes from Pseudoplusia includens

A serpin (CvT-serpin15) of teratocytes contributes to microbial-resistance in Plutella xylostella during Cotesia vestalis parasitism

BACKGROUND

Parasitic wasps are an important group of entomophagous insects for pest control. As parasitic wasps often lay eggs on or into their associated hosts, parasitoids evolve to utilize several factors including venom, polydnavirus (PDV) to alter host physiology for successful parasitism. Some taxa of endoparasitoids produce teratocytes, which are a type of cell that is released into host insects when wasp eggs hatch. Teratocytes display multifunction in parasitism such as host nutritional exploration, immune and developmental regulation, by secreting plenty of proteins into host hemocoel.

RESULTS

A serpin (CvT-serpin15) secreted by teratocytes was characterized. QPCR results showed the expressional level of CvT-serpin15 was upregulated following bacterial challenges. Enzyme activity experiment indicated the recombinant CvT-serpin15 protein could interfere with the growth of Gram-positive bacteria Staphylococcus aureus. The survival rate assay demonstrated CvT-serpin15 increased survival rate of Plutella xylostella infected by S. aureus.

CONCLUSION

CvT-serpin15 secreted by teratocytes would boost the host immune system when pathogens invade host hemocoel during parasitism, and ultimately protect the development of wasp larva from bacterial infection. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Plant-phenotypic changes induced by parasitoid ichnoviruses enhance the performance of both unparasitized and parasitized caterpillars

There is increasing awareness that interactions between plants and insects can be mediated by microbial symbionts. Nonetheless, evidence showing that symbionts associated with organisms beyond the second trophic level affect plant‐insect interactions are restricted to a few cases belonging to parasitoid‐associated bracoviruses. Insect parasitoids harbour a wide array of symbionts which, like bracoviruses, can be injected into their herbivorous hosts to manipulate their physiology and behaviour. Yet, the function of these symbionts in plant‐based trophic webs remains largely overlooked. Here, we provide the first evidence of a parasitoid‐associated symbiont belonging to the group of ichnoviruses which affects the strength of plant‐insect interactions. A comparative proteomic analysis shows that, upon parasitoid injection of calyx fluid containing ichnovirus particles, the composition of salivary glands of caterpillars changes both qualitatively (presence of two viral‐encoded proteins) and quantitatively (abundance of several caterpillar‐resident enzymes, including elicitors such as glucose oxidase). In turn, plant phenotypic changes triggered by the altered composition of caterpillar oral secretions affect the performance of herbivores. Ichnovirus manipulation of plant responses to herbivory leads to benefits for their parasitoid partners in terms of reduced developmental time within the parasitized caterpillar. Interestingly, plant‐mediated ichnovirus‐induced effects also enhance the performances of unparasitized herbivores which in natural conditions may feed alongside parasitized ones. We discuss these findings in the context of ecological costs imposed to the plant by the viral symbiont of the parasitoid. Our results provide intriguing novel findings about the role played by carnivore‐associated symbionts on plant‐insect‐parasitoid systems and underline the importance of placing mutualistic associations in an ecological perspective.

Plants impact cellular immunity of caterpillars to an entomovirus

BACKGROUND

Tri-trophic interactions among plants, insect herbivores and entomopathogens are one of the hot topics in ecology. Although plants have been shown to impact the interactions between herbivores and entomopathogens, it is still unclear how plants affect the cellular immunity of herbivores to entomopathogens.

RESULTS

The number of hemocytes and the proportion of two main cell types (granular hemocytes and plasmatocytes), plasmatocyte-spreading rate, apoptosis rate, two Spodoptera exigua caspase (SeCasp-1, SeCasp-5) activities and gene expressions were all higher and the activities and gene expression of S. exigua inhibitor of apoptosis protein (SeIAP) were lower in nucleopolyhedrovirus (NPV)-infected caterpillars fed Ipomoea aquatica than those fed other plants or artificial diet. Scanning electron microscopy images were consistent with molecular patterns of immune responses.

CONCLUSION

This study suggests that host plants affect the immune responses of herbivores to entomopathogens by manipulating the composition, morphology and apoptosis of herbivore hemocytes, which sheds light on the mechanisms that allow host plants to influence multi-trophic interactions. © 2021 Society of Chemical Industry.

MicroRNAs from Snellenius manilae bracovirus regulate innate and cellular immune responses of its host Spodoptera litura

To avoid inducing immune and physiological responses in insect hosts, parasitoid wasps have developed several mechanisms to inhibit them during parasitism, including the production of venom, specialized wasp cells, and symbioses with polydnaviruses (PDVs). These mechanisms alter the host physiology to give the wasp offspring a greater chance of survival. However, the molecular mechanisms for most of these alterations remain unclear. In the present study, we applied next-generation sequencing analysis and identified several miRNAs that were encoded in the genome of Snellenius manilae bracovirus (SmBV), and expressed in the host larvae, Spodoptera litura, during parasitism. Among these miRNAs, SmBV-miR-199b-5p and SmBV-miR-2989 were found to target domeless and toll-7 in the host, which are involved in the host innate immune responses. Microinjecting the inhibitors of these two miRNAs into parasitized S. litura larvae not only severely decreased the pupation rate of Snellenius manilae, but also restored the phagocytosis and encapsulation activity of the hemocytes. The results demonstrate that these two SmBV-encoded miRNAs play an important role in suppressing the immune responses of parasitized hosts. Overall, our study uncovers the functions of two SmBV-encoded miRNAs in regulating the host innate immune responses upon wasp parasitism.

Microbial Symbionts of Parasitoids

Parasitoids depend on other insects for the development of their offspring. Their eggs are laid in or on a host insect that is consumed during juvenile development. Parasitoids harbor a diversity of microbial symbionts including viruses, bacteria, and fungi. In contrast to symbionts of herbivorous and hematophagous insects, parasitoid symbionts do not provide nutrients. Instead, they are involved in parasitoid reproduction, suppression of host immune responses, and manipulation of the behavior of herbivorous hosts. Moreover, recent research has shown that parasitoid symbionts such as polydnaviruses may also influence plant-mediated interactions among members of plant-associated communities at different trophic levels, such as herbivores, parasitoids, and hyperparasitoids. This implies that these symbionts have a much more extended phenotype than previously thought. This review focuses on the effects of parasitoid symbionts on direct and indirect species interactions and the consequences for community ecology.

Immune response and susceptibility to Cotesia flavipes parasitizing Diatraea saccharalis larvae exposed to and surviving an LC25 dosage of Bacillus thuringiensis

Biological control using entomopathogens and natural enemies is an ecofriendly method for pest management in agriculture. Biological control agents often can be simultaneously employed and compatibility between agents may improve pest suppression. We investigated the influence of the entomopathogen Bacillus thuringiensis (Bt) on the immune system of the sugarcane borer Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) to determine if such changes impact parasitization by Cotesia flavipes Cameron, 1891 (Hymenoptera: Braconidae). The immune response of surviving D. saccharalis larvae fed with an LC₂₅ dosage of a Bt-based biopesticide (Dipel®) was analyzed (total hemocyte count, hemocyte adhesion, and activities of phenoloxidase and lysozyme). Furthermore, the suitability of surviving Bt-fed larvae as hosts for C. flavipes was assessed by measuring parasitoid attributes such as number and size of teratocytes, weight of pupae, length of adult female tibia and number of emerged adults. Total hemocyte count, but not hemocyte adhesion, total protein content and phenoloxidase activity increased in the hemolymph of non-parasitized Bt-fed larvae (Bt-NP) compared to control larvae (NBt-NP). Lysozyme activity increased only after parasitization without Bt exposure (NBt-P). After parasitization, the immunological parameters activated in Bt-NP larvae decreased to levels at or below those observed in control larvae, showing that C. flavipes can regulate the activated immune response of Bt-fed larvae. The development of C. flavipes was not impaired in Bt-fed larval hosts (Bt-P); no changes were observed for teratocyte size, weight of pupal mass, length of hind tibia and number of adults emerged.

Alteration of the phagocytosis and antimicrobial defense of Octodonta nipae (Coleoptera: Chrysomelidae) pupae to Escherichia coli following parasitism by Tetrastichus brontispae (Hymenoptera: Eulophidae)

Although parasites and microbial pathogens are both detrimental to insects, little information is currently available on the mechanism involved in how parasitized hosts balance their immune responses to defend against microbial infections. We addressed this in the present study by comparing the immune response between unparasitized and parasitized pupae of the chrysomelid beetle, Octodonta nipae (Maulik), to Escherichia coli invasion. In an in vivo survival assay, a markedly reduced number of E. coli colony-forming units per microliter was detected in parasitized pupae at 12 and 24 h post-parasitism, together with decreased phagocytosis and enhanced bactericidal activity at 12 h post-parasitism. The effects that parasitism had on the mRNA expression level of selected antimicrobial peptides (AMPs) of O. nipae pupae showed that nearly all transcripts of AMPs examined were highly upregulated during the early and late parasitism stages except defensin 2B, whose mRNA expression level was downregulated at 24 h post-parasitism. Further elucidation on the main maternal fluids responsible for alteration of the primary immune response against E. coli showed that ovarian fluid increased phagocytosis at 48 h post-injection. These results indicated that the enhanced degradation of E. coli in parasitized pupae resulted mainly from the elevated bactericidal activity without observing the increased transcripts of target AMPs. This study contributes to a better understanding of the mechanisms involved in the immune responses of a parasitized host to bacterial infections.

Recent Advances in the Use of Galleria mellonella Model to Study Immune Responses against Human Pathogens

The use of invertebrates for in vivo studies in microbiology is well established in the scientific community. Larvae of Galleria mellonella are a widely used model for studying pathogenesis, the efficacy of new antimicrobial compounds, and immune responses. The immune system of G. mellonella larvae is structurally and functionally similar to the innate immune response of mammals, which makes this model suitable for such studies. In this review, cellular responses (hemocytes activity: phagocytosis, nodulation, and encapsulation) and humoral responses (reactions or soluble molecules released in the hemolymph as antimicrobial peptides, melanization, clotting, free radical production, and primary immunization) are discussed, highlighting the use of G. mellonella as a model of immune response to different human pathogenic microorganisms.

Cotesia vestalis teratocytes express a diversity of genes and exhibit novel immune functions in parasitism

Some endoparasitoid wasps lay eggs that produce cells called teratocytes. In this study, we sequenced and analyzed the transcriptome of teratocytes from the solitary endoparasitoid Cotesia vestalis (Braconidae), which parasitizes larval stage Plutella xylostella (Plutellidae). Results identified many teratocyte transcripts with potential functions in affecting host immune defenses, growth or metabolism. Characterization of teratocyte-secreted venom-like protein 8 (TSVP-8) indicated it inhibits melanization of host hemolymph in vitro, while two predicted anti-microbial peptides (CvT-def 1 and 3) inhibited the growth of bacteria. Results also showed the parasitized hosts lacking teratocytes experienced higher mortality after immune challenge by pathogens than hosts with teratocytes. Taken together, these findings indicate that C. vestalis teratocytes secrete products that alter host immune functions while also producing anti-microbial peptides with functions that help protect the host from infection by other organisms.

Venom of Parasitoid Pteromalus puparum Impairs Host Humoral Antimicrobial Activity by Decreasing Host Cecropin and Lysozyme Gene Expression

Insect host/parasitoid interactions are co-evolved systems in which host defenses are balanced by parasitoid mechanisms to disable or hide from host immune effectors. Here, we report that Pteromalus puparum venom impairs the antimicrobial activity of its host Pieris rapae. Inhibition zone results showed that bead injection induced the antimicrobial activity of the host hemolymph but that venom inhibited it. The cDNAs encoding cecropin and lysozyme were screened. Relative quantitative PCR results indicated that all of the microorganisms and bead injections up-regulated the transcript levels of the two genes but that venom down-regulated them. At 8 h post bead challenge, there was a peak in the transcript level of the cecropin gene, whereas the peak of lysozyme gene occurred at 24 h. The transcripts levels of the two genes were higher in the granulocytes and fat body than in other tissues. RNA interference decreased the transcript levels of the two genes and the antimicrobial activity of the pupal hemolymph. Venom injections similarly silenced the expression of the two genes during the first 8 h post-treatment in time- and dose-dependent manners, after which the silence effects abated. Additionally, recombinant cecropin and lysozyme had no significant effect on the emergence rate of pupae that were parasitized by P. puparum females. These findings suggest one mechanism of impairing host antimicrobial activity by parasitoid venom.

Variation in a Host-Parasitoid Interaction across Independent Populations

Antagonistic relationships between parasitoids and their insect hosts involve multiple traits and are shaped by their ecological and evolutionary context. The parasitoid wasp Cotesia melitaearum and its host butterfly Melitaea cinxia occur in several locations around the Baltic sea, with differences in landscape structure, population sizes and the histories of the populations. We compared the virulence of the parasitoid and the susceptibility of the host from five populations in a reciprocal transplant-style experiment using the progeny of five independent host and parasitoid individuals from each population. The host populations showed significant differences in the rate of encapsulation and parasitoid development rate. The parasitoid populations differed in brood size, development rate, pupal size and adult longevity. Some trait differences depended on specific host-parasitoid combinations, but neither species performed systematically better or worse in experiments involving local versus non-local populations of the other species. Furthermore, individuals from host populations with the most recent common ancestry did not perform alike, and there was no negative effect due to a history of inbreeding in the parasitoid. The complex pattern of variation in the traits related to the vulnerability of the host and the ability of the parasitoid to exploit the host may reflect multiple functions of the traits that would hinder simple local adaptation.

Pteromalus puparum venom impairs host cellular immune responses by decreasing expression of its scavenger receptor gene

Insect host/parasitoid interactions are co-evolved systems in which host defenses are balanced by parasitoid mechanisms to disable or hide from host immune effectors. Although there is a rich literature on these systems, parasitoid immune-disabling mechanisms have not been fully elucidated. Here we report on a newly discovered immune-disabling mechanism in the Pieris rapae/Pteromalus puparum host/parasitoid system. Because venom injections and parasitization suppresses host phagocytosis, we turned attention to the P. rapae scavenger receptor (Pr-SR), posing the hypothesis that P. puparum venom suppresses expression of the host Pr-SR gene. To test our hypothesis, we cloned a full-length cDNA of the Pr-SR. Multiple sequences alignment showed the deduced amino acid sequence of Pr-SR is similar to scavenger receptors of other lepidopterans. Bacterial and bead injections induced Pr-SR mRNA and protein expression, which peaked at 4h post-bead injection. Venom injection inhibited Pr-SR expression. Pr-SR was specifically expressed in granulocytes compared to plasmatocytes. We localized the Pr-SR protein in cytoplasm and cellular membrane, with no evidence of secretion into host plasma. Double-strand RNA designed to Pr-SR mRNA silenced expression of Pr-SR and significantly impaired host phagocytosis and encapsulation reactions. Venom injections similarly silenced Pr-SR expression during the first 8h post-treatment, after which the silencing effects gradually abated. We infer from these findings that one mechanism of impairing P. rapae hemocytic immune reactions is by silencing expression of Pr-SR.

Venom of parasitoid, Pteromalus puparum, suppresses host, Pieris rapae, immune promotion by decreasing host C-type lectin gene expression

Background

Insect hosts have evolved immunity against invasion by parasitoids, and in co-evolutionary response parasitoids have also developed strategies to overcome host immune systems. The mechanisms through which parasitoid venoms disrupt the promotion of host immunity are still unclear. We report here a new mechanism evolved by parasitoid Pteromalus puparum, whose venom inhibited the promotion of immunity in its host Pieris rapae (cabbage white butterfly).

Methodology/Principal Findings

A full-length cDNA encoding a C-type lectin (Pr-CTL) was isolated from P. rapae. Quantitative PCR and immunoblotting showed that injection of bacterial and inert beads induced expression of Pr-CTL, with peaks of mRNA and Pr-CTL protein levels at 4 and 8 h post beads challenge, respectively. In contrast, parasitoid venom suppressed Pr-CTL expression when co-injected with beads, in a time and dose-dependent manner. Immunolocalization and immunoblotting results showed that Pr-CTL was first detectable in vesicles present in cytoplasm of granulocytes in host hemolymph, and was then secreted from cells into circulatory fluid. Finally, the secreted Pr-CTL bound to cellular membranes of both granulocytes and plasmatocytes. Injection of double-stranded RNA specific for target gene decreased expression of Pr-CTL, and a few other host immune-related genes. Suppression of Pr-CTL expression also down-regulated antimicrobial and phenoloxidase activities, and reducing phagocytotic and encapsulation rates in host. The inhibitory effect of parasitoid venom on host encapsulation is consistent with its effect in suppressing Pr-CTL expression. Binding assay results showed that recombinant Pr-CTL directly attached to the surface of P. puparum egges. We infer that Pr-CTL may serve as an immune signalling co-effector, first binding to parasitoid eggs, regulating expression of a set of immune-related genes and promoting host immunity.

Conclusions/Significance

P. puparum venom inhibits promotion of host immune responses by silencing expression of host C-type lectin gene Pr-CTL, whose expression affected transcription of other host immune-related genes.

The protein P23 identifies capsule-forming plasmatocytes in the moth Pseudoplusia includens

The moth Pseudoplusia includens produces four types of hemocytes named granulocytes, plasmatocytes, spherule cells and oenocytoids. Prior studies established that the main function of plasmatocytes in P. includens is encapsulation of parasitoids and other foreign entitites. P. includens plasmatocytes are also recognized by several monoclonal antibodies that bind unknown antigens. Of particular interest is the antibody 43E9A10 whose binding properties indicate that plasmatocytes consist of two subpopulations: cells that can spread on foreign surfaces and cells that cannot. Here we report 43E9A10 recognizes P23, which is a member of the aegerolysin protein family. Expression analyses confirmed that p23 is specifically expressed in plasmatocytes. Functional studies indicated that only P23-expressing plasmatocytes form capsules and spread in response to the cytokine plasmatocyte spreading peptide. In contrast, P23 showed no antibacterial or cytolytic activity toward bacteria and mammalian erythrocytes. Overall, our results suggest that P23 is a maturation marker that identifies capsule-forming plasmatocytes.

Socialized medicine: individual and communal disease barriers in honey bees

Honey bees are attacked by numerous parasites and pathogens toward which they present a variety of individual and group-level defenses. In this review, we briefly introduce the many pathogens and parasites afflicting honey bees, highlighting the biology of specific taxonomic groups mainly as they relate to virulence and possible defenses. Second, we describe physiological, immunological, and behavioral responses of individual bees toward pathogens and parasites. Third, bees also show behavioral mechanisms for reducing the disease risk of their nestmates. Accordingly, we discuss the dynamics of hygienic behavior and other group-level behaviors that can limit disease. Finally, we conclude with several avenues of research that seem especially promising for understanding host-parasite relationships in bees and for developing breeding or management strategies for enhancing honey bee health. We discuss how human efforts to maintain healthy colonies intersect with similar efforts by the bees, and how bee management and breeding protocols can affect disease traits in the short and long term.

Protein tyrosine phosphatase-H2 from a polydnavirus induces apoptosis of insect cells

The family Polydnaviridae is a large group of immunosuppressive insect viruses that are symbiotically associated with parasitoid wasps. The polydnavirus Microplitis demolitor bracovirus (MdBV) causes several alterations that disable the cellular and humoral immune defences of host insects, including apoptosis of the primary phagocytic population of circulating immune cells (haemocytes), called granulocytes. Here, we show that MdBV infection causes granulocytes in the lepidopteran Spodoptera frugiperda to apoptose. An expression screen conducted in the S. frugiperda 21 cell line identified the MdBV gene ptp-H2 as an apoptosis inducer, as indicated by cell fragmentation, annexin V binding, mitochondrial membrane depolarization and caspase activation. PTP-H2 is a classical protein tyrosine phosphatase that has been shown previously to function as an inhibitor of phagocytosis. PTP-H2-mediated death of Sf-21 cells was blocked by the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-(O-methyl) Asp-fluoromethylketone (Z-VAD-FMK), but cells maintained in this inhibitor still exhibited a suppressed phagocytic response. Mutagenesis experiments indicated that the essential catalytic cysteine residue required for the phosphatase activity of PTP-H2 was required for apoptotic activity in Sf-21 cells. Loss of adhesion was insufficient to stimulate apoptosis of Sf-21 cells. PTP-H2 expression, however, did significantly reduce proliferation of Sf-21 cells, which could contribute to the apoptotic activity of this viral gene. Overall, our results indicate that specific genes expressed by MdBV induce apoptosis of certain insect cells and that this activity contributes to immunosuppression of hosts.

Two homologous parasitism-specific proteins encoded in Cotesia plutellae bracovirus and their expression profiles in parasitized Plutella xylostella

A wasp, Cotesia plutellae, parasitizes the diamondback moth, Plutella xylostella, and interrupts host physiology for wasp survival and development. Identification of parasitism-specific factors would be helpful to understand the host-parasitoid interaction. This study focused on identification of a 15-kDa protein found only in plasma of the parasitized P. xylostella. Degenerate primers were designed after N-terminal amino acid sequencing of the parasitism-specific protein and used to clone the corresponding gene from the parasitized P. xylostella by a nested reverse transcriptase-polymerase chain reaction (RT-PCR). Two homologous genes were cloned and identified as "CpBV15alpha" and "CpBV15beta," respectively, due to the identical size (158 amino acid residues) of the predicted open reading frames, in which they shared amino acid sequences in both terminal regions, but varied in internal sequences. Southern hybridization analysis indicated that both genes were located on C. plutellae bracovirus genome. Real-time quantitative RT-PCR revealed that both genes were mostly expressed at the late parasitization period, which was further confirmed by an immunoblotting assay using CpBV15 antibody. A recombinant CpBV15 protein was produced from Sf9 cells via a baculovirus expression system. The purified CpBV15 protein could enter hemocytes of P. xylostella and were localized in the cytosol. Along with the sequence similarities of CpBV15s with eukaryotic initiation factors, their putative biological role has been discussed in terms of the host translation inhibitory factor.

An entomopathogenic bacterium, Xenorhabdus nematophila, inhibits hemocyte phagocytosis of Spodoptera exigua by inhibiting phospholipase A2

Phagocytosis is a hemocytic behavior against bacterial infection. An entomopathogenic bacterium, Xenorhabdus nematophila, inhibits immune responses of target insects and causes hemolymph septicemia. This study analyzed how X. nematophila could inhibit phagocytosis to increase its pathogenicity. Granular cells and plasmatocytes were the main phagocytic hemocytes of Spodoptera exigua determined by observing fluorescence-labeled bacteria in the cytosol. X. nematophila significantly inhibited phagocytosis of both hemocytes, while heat-killed X. nematophila lost its inhibitory potency. However, co-injection of X. nematophila with arachidonic acid did not show any significant inhibition of hemocyte phagocytosis. In fact, hemocytes of S. exigua infected with X. nematophila showed significant reduction in phospholipase A(2) (PLA(2)) activity. Dexamethasone, a specific PLA(2) inhibitor, significantly inhibited phagocytosis of both cell types. However, the inhibitory effect of dexamethasone was recovered by addition of arachidonic acid. Incubation of hemocytes with benzylideneacetone, a metabolite of X. nematophila, inhibited phagocytosis in a dose-dependent manner. These results suggest that X. nematophila produces and secretes PLA(2) inhibitor(s), which in turn inhibit the phagocytic response of hemocytes.

PTP-H2 and PTP-H3 from Microplitis demolitor Bracovirus localize to focal adhesions and are antiphagocytic in insect immune cells

Viruses in the family Polydnaviridae are symbiotically associated with parasitoid wasps. Wasps inject polydnaviruses (PDVs) when laying an egg into their insect host, and expression of viral gene products causes several physiological alterations, including immunosuppression, that allow the wasp's progeny to develop. As with other PDVs, most Microplitis demolitor bracovirus (MdBV) genes are related variants that form gene families. The largest MdBV gene family includes 13 members that encode predicted proteins related to protein tyrosine phosphatases (PTPs). Sequence analysis during the present study indicated that five PTP family members (PTP-H2, -H3, -N1, and -N2) have fully conserved catalytic domains, whereas other family members exhibited replacements, deletions, or rearrangements of amino acids considered essential for tyrosine phosphatase activity. Expression studies indicated that most MdBV PTP genes are expressed in virus-infected host insects, with transcript abundance usually being highest in hemocytes. MdBV-infected hemocytes also exhibited higher levels of tyrosine phosphatase activity than noninfected hemocytes. We produced expression constructs for four of the most abundantly expressed PTP family members and conducted functional studies with hemocyte-like Drosophila S2 cells. These experiments suggested that recombinant PTP-H2 and PTP-H3 are functional tyrosine phosphatases whereas PTP-H1 and PTP-J1 are not. PTP-H2 and -H3 localized to focal adhesions in S2 cells, and coexpression with another MdBV gene product, Glc1.8, resulted in complete inhibition of phagocytosis.

Characterization of hemocytes from the mosquitoes Anopheles gambiae and Aedes aegypti

Hemocytes are an essential component of the mosquito immune system but current knowledge of the types of hemocytes mosquitoes produce, their relative abundance, and their functions is limited. Addressing these issues requires improved methods for collecting and maintaining mosquito hemocytes in vitro, and comparative data that address whether important vector species produce similar or different hemocyte types. Toward this end, we conducted a comparative study with Anopheles gambiae and Aedes aegypti. Collection method greatly affected the number of hemocytes and contaminants obtained from adult females of each species. Using a collection method called high injection/recovery, we concluded that hemolymph from An. gambiae and Ae. aegypti adult females contains three hemocyte types (granulocytes, oenocytoids and prohemocytes) that were distinguished from one another by a combination of morphological and functional markers. Significantly more hemocytes were recovered from An. gambiae females than Ae. aegypti. However, granulocytes were the most abundant cell type in both species while oenocytoids and prohemocytes comprised less than 10% of the total hemocyte population. The same hemocyte types were collected from larvae, pupae and adult males albeit the absolute number and proportion of each hemocyte type differed from adult females. The number of hemocytes recovered from sugar fed females declined with age but blood feeding transiently increased hemocyte abundance. Two antibodies tested as potential hemocyte markers (anti-PP06 and anti-Dox-A2) also exhibited alterations in staining patterns following immune challenge with the bacterium Escherichia coli.

Parasitism by Cotesia plutellae alters the hemocyte population and immunological function of the diamondback moth, Plutella xylostella

Cotesia plutellae, a solitary endoparasitoid wasp, parasitizes the diamondback moth, Plutella xylostella, and induces host immunosuppression and lethality in the late larval stage. This study focused on changes of cellular immunity in the parasitized P. xylostella in terms of hemocyte composition and cellular functions. In third and fourth instar larvae of nonparasitized P. xylostella, granular cells represented the main hemocyte type (60-70%) and plasmatocytes were also present at around 15% among the total hemocytes. Following parasitization by C. plutellae, the relative proportions of these two major hemocytes changed very little, but the total hemocyte counts exhibited a significant reduction. Functionally, the granular cells played a significant role in phagocytosis based on a fluorescence assay using fluorecein isothiocyanate-labeled bacteria. The phagocytic activity of the granular cells occurred as early as 5 min after incubation with the bacteria, and increased during the first 40 min of incubation. The parasitism by C. plutellae significantly inhibited phagocytosis of the granular cells. Plasmatocytes also exhibited minor phagocytic activity. Moreover, plasmatocyte phagocytosis was not inhibited by parasitism. On the other hand, hemocyte-spreading behavior in response to pathogen infection was significant only for plasmatocytes, which exhibited a characteristic spindle shape upon infection. A significant spreading of the plasmatocytes was found as early as 5 min after pathogen incubation and their ratio increased during the first 40 min. An insect cytokine, plasmatocyte-spreading peptide 1 (PSP1) from Pseudoplusia includens, was highly active in inducing plasmatocyte-spreading behavior of P. xylostella in a dose-dependent manner. P. xylostella parasitized by C. plutella was significantly inhibited in plasmatocyte-spreading in response to an active dose of PSP1. An in vivo encapsulation assay showed that the parasitized P. xylostella could not effectively form the hemocyte capsules around injected agarose beads. This research demonstrates that the parasitism of C. plutellae adversely affects the total hemocyte populations in number and function, which would contribute to host immunosuppression.

A review of insect stem cell types

Insect stem cells have been described from both embryonic and adult tissues from a diversity of insect species, although much of the focus in insect stem cell research has been on Drosophila. Insects are a vast and diverse group and it is surprising that a critical aspect of their development like stem cells has not received more attention. In this review we discuss the current state of knowledge of insect stem cell types. We examine what stem cell types have been identified from insects, and briefly discuss what is known about their regulation.