JNK MAP kinase is involved in the humoral immune response of the greater wax moth larvae Galleria mellonella

Ben-JNK signaling is required for host mortality during Periplaneta fuliginosa densovirus infection

BACKGROUND

Cockroaches are widely acknowledged as significant vectors of pathogenic microorganisms. The Periplaneta fuliginosa densovirus (PfDNV) infects the smoky-brown cockroach P. fuliginosa and causes host mortality, which identifies the PfDNV as a species-specific and environmentally friendly biopesticide. However, although the biochemical characterization of PfDNV has been extensively studied, the immune response against PfDNV remains largely unclear.

RESULTS

Here, we investigated the replication of PfDNV and its associated pathological phenotype in the foregut and hindgut. Consequently, we dissected and performed transcriptome sequencing on the foregut, midgut, and hindgut separately. We revealed the up-regulation of immune response signaling pathway c-Jun N-terminal kinase (JNK) and apoptosis in response to viral infection. Furthermore, knockdown of the JNK upstream gene Ben resulted in a decrease in virus titer and delayed host mortality.

CONCLUSION

Taken together, our findings provide evidence that the Ben-JNK signaling plays a crucial role in PfDNV infection, leading to excessive apoptosis in intestinal tissues and ultimately resulting in the death of the host. Our results indicated that the host response to PfDNV fosters viral infection, thereby increasing host lethality. This underscores the potential of PfDNV as a viable, environmentally friendly biopesticide. © 2024 Society of Chemical Industry.

Alternative splicing landscape of small brown planthopper and different response of JNK2 isoforms to rice stripe virus infection

Alternative splicing (AS) is a frequent posttranscriptional regulatory event occurring in response to various endogenous and exogenous stimuli in most eukaryotic organisms. However, little is known about the effects of insect-transmitted viruses on AS events in insect vectors. The present study used third-generation sequencing technology and RNA sequencing (RNA-Seq) to evaluate the AS response in the small brown planthopper Laodelphax striatellus to rice stripe virus (RSV). The full-length transcriptome of L. striatellus was obtained using single-molecule real-time sequencing technology (SMRT). Posttranscriptional regulatory events, including AS, alternative polyadenylation, and fusion transcripts, were analyzed. A total of 28,175 nonredundant transcript isoforms included 24,950 transcripts assigned to 8,500 annotated genes of L. striatellus, and 5,000 of these genes (58.8%) had AS events. RNA-Seq of the gut samples of insects infected by RSV for 8 d identified 3,458 differentially expressed transcripts (DETs); 2,185 of these DETs were transcribed from 1,568 genes that had AS events, indicating that 31.4% of alternatively spliced genes responded to RSV infection of the gut. One of the c-Jun N-terminal kinase (JNK) genes, JNK2, experienced exon skipping, resulting in three transcript isoforms. These three isoforms differentially responded to RSV infection during development and in various organs. Injection of double-stranded RNAs targeting all or two isoforms indicated that three or at least two JNK2 isoforms facilitated RSV accumulation in planthoppers. These results implied that AS events could participate in the regulation of complex relationships between viruses and insect vectors. Importance Alternative splicing (AS) is a regulatory mechanism that occurs after gene transcription. AS events can enrich protein diversity to promote the reactions of the organisms to various endogenous and exogenous stimulations. It is not known how insect vectors exploit AS events to cope with transmitted viruses. The present study used third-generation sequencing technology to obtain the profile of AS events in the small brown planthopper Laodelphax striatellus, which is an efficient vector for rice stripe virus (RSV). The results indicated that 31.4% of alternatively spliced genes responded to RSV infection in the gut of planthoppers. One of the c-Jun N-terminal kinase (JNK) genes, JNK2, produced three transcript isoforms by AS. These three isoforms showed different responses to RSV infection, and at least two isoforms facilitated viral accumulation in planthoppers. These results implied that AS events could participate in the regulation of complex relationships between viruses and insect vectors.

JNK pathway plays a key role in the immune system of the pea aphid and is regulated by microRNA-184

Different from holometabolous insects, the hemipteran species such as pea aphid Acyrthosiphon pisum exhibit reduced immune responses with the absence of the genes coding for antimicrobial peptide (AMP), immune deficiency (IMD), peptidoglycan recognition proteins (PGRPs), and other immune-related molecules. Prior studies have proved that phenoloxidase (PO)-mediated melanization, hemocyte-mediated phagocytosis, and reactive oxygen species (ROS) participate in pea aphid defense against bacterial infection. Also, the conserved signaling, Jun N-terminal kinase (JNK) pathway, has been suggested to be involved in pea aphid immune defense. However, the precise role of the JNK signaling, its interplay with other immune responses and its regulation in pea aphid are largely unknown. In this study, using in vitro biochemical assays and in vivo bioassays, we demonstrated that the JNK pathway regulated hemolymph PO activity, hydrogen peroxide concentration and hemocyte phagocytosis in bacteria infected pea aphids, suggesting that the JNK pathway plays a central role in regulating immune responses in pea aphid. We further revealed the JNK pathway is regulated by microRNA-184 in response to bacterial infection. It is possible that in common the JNK pathway plays a key role in immune system of hemipteran insects and microRNA-184 regulates the JNK pathway in animals.

Autosomal and Mitochondrial Adaptation Following Admixture: A Case Study on the Honeybees of Reunion Island

The honeybee population of the tropical Reunion Island is a genetic admixture of the Apis mellifera unicolor subspecies, originally described in Madagascar, and of European subspecies, mainly A. m. carnica and A. m. ligustica, regularly imported to the island since the late 19th century. We took advantage of this population to study genetic admixing of the tropical-adapted indigenous and temperate-adapted European genetic backgrounds. Whole genome sequencing of 30 workers and 6 males from Reunion, compared with samples from Europe, Madagascar, Mauritius, Rodrigues, and the Seychelles, revealed the Reunion honeybee population to be composed on an average of 53.2 ± 5.9% A. m. unicolor nuclear genomic background, the rest being mainly composed of A. m. carnica and to a lesser extent A. m. ligustica. In striking contrast to this, only 1 out of the 36 honeybees from Reunion had a mitochondrial genome of European origin, suggesting selection has favored the A. m. unicolor mitotype, which is possibly better adapted to the island’s bioclimate. Local ancestry was determined along the chromosomes for all Reunion samples, and a test for preferential selection for the A. m. unicolor or European background revealed 15 regions significantly associated with the A. m. unicolor lineage and 9 regions with the European lineage. Our results provide insights into the long-term consequences of introducing exotic specimen on the nuclear and mitochondrial genomes of locally adapted populations.

Alimentary Tract Transcriptome Analysis of the Tea Geometrid, Ectropis oblique (Lepidoptera: Geometridae)

Ectropis oblique Prout (Lepidoptera: Geometridae) is one of the main pests that damages the tea crop in Southeast Asia. To understand the molecular mechanisms of its feeding biology, transcriptomes of the alimentary tract (AT) and of the body minus the AT of E. oblique were successfully sequenced and analyzed in this study. A total of 36,950 unigenes from de novo sequences were assembled. After analysis using six annotation databases (e.g., Gene Ontology, Kyoto Encyclopedia of Genes and Genome, and NCBI nr), a series of putative genes were found for this insect species that were related to digestion, detoxification, the immune system, and Bacillus thuringiensis (Bt) receptors. From this series of genes, 21 were randomly selected to verify the relative expression levels of transcripts using quantitative real-time polymerase chain reaction. These results will provide an invaluable genomic resource for future studies on the molecular mechanisms of E. oblique, which will be useful in developing biological control strategies for this pest.

Novel approach to study gastropod-mediated innate immune reactions against metastrongyloid parasites

The anthropozoonotic metastrongyloid nematodes Angiostrongylus cantonensis and Angiostrongylus costaricensis, as well as Angiostrongylus vasorum, Crenosoma vulpis, Aelurostrongylus abstrusus and Troglostrongylus brevior are currently considered as emerging gastropod-borne parasites and have gained growing scientific attention in the last years. However, the knowledge on invertebrate immune responses and on how metastrongyloid larvae are attacked by gastropod immune cells is still limited. This work aims to describe an in vitro system to investigate haemocyte-derived innate immune responses of terrestrial gastropods induced by vital axenic metastrongyloid larvae. We also provide protocols on slug/snail management and breeding under standardized climate conditions (circadian cycle, temperature and humidity) for the generation of parasite-free F0 stages which are essential for immune-related investigations. Adult slug species (Arion lusitanicus, Limax maximus) and giant snails (Achatina fulica) were maintained in fully automated climate chambers until mating and production of fertilized eggs. Newly hatched F0 juvenile specimens were kept under parasite-free conditions before experimental use. An improved protocol for gastropod haemolymph collection and haemocyte isolation was established. Giemsa-stained haemolymph preparations showed adequate haemocyte isolation in all three gastropod species. Additionally, a protocol for the production of axenic first and third stage larvae (L1, L3) was established. Haemocyte functionality was tested in haemocyte-nematode-co-cultures. Scanning electron microscopy (SEM) and light microscopy analyses revealed that gastropod-derived haemocytes formed clusters as well as DNA-rich extracellular aggregates catching larvae and decreasing their motility. These data confirm the usefulness of the presented methods to study haemocyte-mediated gastropod immune responses to better understand the complex biology of gastropod-borne diseases.

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

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

Immunity of the greater wax moth Galleria mellonella

Investigation of insect immune mechanisms provides important information concerning innate immunity, which in many aspects is conserved in animals. This is one of the reasons why insects serve as model organisms to study virulence mechanisms of human pathogens. From the evolutionary point of view, we also learn a lot about host-pathogen interaction and adaptation of organisms to conditions of life. Additionally, insect-derived antibacterial and antifungal peptides and proteins are considered for their potential to be applied as alternatives to antibiotics. While Drosophila melanogaster is used to study the genetic aspect of insect immunity, Galleria mellonella serves as a good model for biochemical research. Given the size of the insect, it is possible to obtain easily hemolymph and other tissues as a source of many immune-relevant polypeptides. This review article summarizes our knowledge concerning G. mellonella immunity. The best-characterized immune-related proteins and peptides are recalled and their short characteristic is given. Some other proteins identified at the mRNA level are also mentioned. The infectious routes used by Galleria natural pathogens such as Bacillus thuringiensis and Beauveria bassiana are also described in the context of host-pathogen interaction. Finally, the plasticity of G. mellonella immune response influenced by abiotic and biotic factors is described.

Insect immunology and hematopoiesis

Insects combat infection by mounting powerful immune responses that are mediated by hemocytes, the fat body, the midgut, the salivary glands and other tissues. Foreign organisms that have entered the body of an insect are recognized by the immune system when pathogen-associated molecular patterns bind host-derived pattern recognition receptors. This, in turn, activates immune signaling pathways that amplify the immune response, induce the production of factors with antimicrobial activity, and activate effector pathways. Among the immune signaling pathways are the Toll, Imd, Jak/Stat, JNK, and insulin pathways. Activation of these and other pathways leads to pathogen killing via phagocytosis, melanization, cellular encapsulation, nodulation, lysis, RNAi-mediated virus destruction, autophagy and apoptosis. This review details these and other aspects of immunity in insects, and discusses how the immune and circulatory systems have co-adapted to combat infection, how hemocyte replication and differentiation takes place (hematopoiesis), how an infection prepares an insect for a subsequent infection (immune priming), how environmental factors such as temperature and the age of the insect impact the immune response, and how social immunity protects entire groups. Finally, this review highlights some underexplored areas in the field of insect immunobiology.

Genome-wide characterization and expression profiling of immune genes in the diamondback moth, Plutella xylostella (L.)

The diamondback moth, Plutella xylostella (L.), is a destructive pest that attacks cruciferous crops worldwide. Immune responses are important for interactions between insects and pathogens and information on these underpins the development of strategies for biocontrol-based pest management. Little, however, is known about immune genes and their regulation patterns in P. xylostella. A total of 149 immune-related genes in 20 gene families were identified through comparison of P. xylostella genome with the genomes of other insects. Complete and conserved Toll, IMD and JAK-STAT signaling pathways were found in P. xylostella. Genes involved in pathogen recognition were expanded and more diversified than genes associated with intracellular signal transduction. Gene expression profiles showed that the IMD pathway may regulate expression of antimicrobial peptide (AMP) genes in the midgut, and be related to an observed down-regulation of AMPs in experimental lines of insecticide-resistant P. xylostella. A bacterial feeding study demonstrated that P. xylostella could activate different AMPs in response to bacterial infection. This study has established a framework of comprehensive expression profiles that highlight cues for immune regulation in a major pest. Our work provides a foundation for further studies on the functions of P. xylostella immune genes and mechanisms of innate immunity.

Changes in the hemolymph protein profiles in Galleria mellonella infected with Bacillus thuringiensis involve apolipophorin III. The effect of heat shock

This report concerns the effect of heat shock on host-pathogen interaction in Galleria mellonella infected with Bacillus thuringiensis. We show enhanced activity against Gram-positive bacteria in the hemolymph of larvae pre-exposed to heat shock before infection with B. thuringiensis. Heat shock influenced the protein pattern in the hemolymph of infected larvae: more peptides with a molecular weight below 10 kDa were detected in comparison with nonshocked animals. Additionally, we noticed that the amount of apolipophorin III (apoLp-III) in the hemolymph decreased transiently following infection, which was considerably higher in larvae pre-exposed to heat shock. On the other hand, its expression in the fat body showed a consequent infection-induced decline, observed equally in shocked and nonshocked animals. This suggests that the amount of apoLp-III in the hemolymph of G. mellonella larvae is regulated at multiple levels. We also report that this protein is more resistant to degradation in the hemolymph of larvae pre-exposed to heat shock in comparison to nonshocked larvae. Two-dimensional analysis revealed the presence of three isoforms of apoLp-III, all susceptible to proteolytic degradation. However, one of them was the most abundant, both in the protease-treated and untreated hemolymph. Taking into consideration that, in general, apoLp-III has a stimulative effect on different immune-related hemolymph proteins and peptides, the reported findings bring us closer to understanding the effect of heat shock on the resistance of G. mellonella to infection.

Contributions of cellular and humoral immunity of Galleria mellonella larvae in defence against oral infection by Bacillus thuringiensis

In this study the cellular and humoral immune reactions of the Greater wax moth Galleria mellonella have been investigated during bacterial infection caused by oral administration of Bacillus thuringiensis. Two different dose strengths were investigated to assess the contribution of immune parameters to induced Bt resistance. Low-dose (sublethal LC15) infection resulted in significantly elevated haemolymph phenoloxidase and lysozyme-like activity, enhanced phagocytic activity of haemocytes, and increased encapsulation responses in infected larvae at 48 and 72 h post infection. Higher doses of Bt (half-lethal LC50) also triggered significantly elevated haemolymph phenoloxidase and lysozyme-like activity, but decreased the coagulation index and activity of phenoloxidase in haemocytes of infected larvae. In both types of infection, the pool of circulating haemocytes became depleted. The importance of cellular and humoral immune reactions in induced insect resistance to intestinal bacterial infection Bt is herein discussed.

Heat shock affects host-pathogen interaction in Galleria mellonella infected with Bacillus thuringiensis

We report that Galleria mellonella larvae exposed to heat shock was more resistant to infection with entomopathogenic bacteria Bacillus thuringiensis. The insects were exposed to a temperature of 40°C for 30 min directly before injection of vegetative bacterial cells. It appeared that the kinetics of the immune response was affected in heat-shocked animals. The infection-induced antimicrobial activity of larval hemolymph was stronger in shocked animals in comparison to the non-shocked ones. Hemolymph proteins of molecular weight below 10 kDa, corresponding to the size of antimicrobial peptides, were responsible for this activity. Furthermore, the transcription level of genes encoding antimicrobial peptides: cecropin, gallerimycin, and galiomycin was increased in the fat bodies of insects exposed to heat shock before infection. On the contrary, the heat-shock treatment did not enhance expression of the metalloproteinase inhibitor-IMPI in the infected animals. The difference in the amount of antimicrobial peptides and, consequently, in the defense activity of insect hemolymph, persisted after the action of bacterial metalloproteinases, which are well-known virulence factors. Furthermore, peptides with antimicrobial activity in the hemolymph of infected larvae pre-exposed to heat shock appeared to be more resistant to proteolytic degradation both in vitro and in vivo. Our results point to the mechanism of cross-protection of thermal stress toward innate immune response.

Insights into the Melipona scutellaris (Hymenoptera, Apidae, Meliponini) fat body transcriptome

The insect fat body is a multifunctional organ analogous to the vertebrate liver. The fat body is involved in the metabolism of juvenile hormone, regulation of environmental stress, production of immunity regulator-like proteins in cells and protein storage. However, very little is known about the molecular mechanisms involved in fat body physiology in stingless bees. In this study, we analyzed the transcriptome of the fat body from the stingless bee Melipona scutellaris. In silico analysis of a set of cDNA library sequences yielded 1728 expressed sequence tags (ESTs) and 997 high-quality sequences that were assembled into 29 contigs and 117 singlets. The BLAST X tool showed that 86% of the ESTs shared similarity with Apis mellifera (honeybee) genes. The M. scutellaris fat body ESTs encoded proteins with roles in numerous physiological processes, including anti-oxidation, phosphorylation, metabolism, detoxification, transmembrane transport, intracellular transport, cell proliferation, protein hydrolysis and protein synthesis. This is the first report to describe a transcriptomic analysis of specific organs of M. scutellaris. Our findings provide new insights into the physiological role of the fat body in stingless bees.

Galleria mellonella infected with Bacillus thuringiensis involves Hsp90

Insects are good models for studying the innate immune response. We report that Galleria mellonella larvae infected with entomopathogenic bacteria Bacillus thuringiensis kurstaki show changes in the level of Hsp90. Our experimental approach was to pre-treat larvae with the Hsp90-binding compound, 17-DMAG, before infection with B. thuringiensis. We show that pre-treated animals display a higher level of immune response. This was mainly manifested by enhanced action of their hemolymph directed toward living bacteria as well as lysozyme activity digesting bacterial peptidoglycan. The observed phenomenon was due to the higher activity of antimicrobial peptides which, in contrast to healthy animals, was detected in the hemolymph of the immunestimulated larvae. Finally, the physiological significance of our observation was highlighted by the fact that G. mellonella pre-treated with 17-DMAG showed a prolonged survival rate after infection with B. thuringiensis than the control animals. Our report points to a role for Hsp90 in the immune response of G. mellonella after infection with B. thuringiensis at the optimal growth temperature.

A strong immune response in young adult honeybees masks their increased susceptibility to infection compared to older bees

Honeybees, Apis mellifera, show age-related division of labor in which young adults perform maintenance (“housekeeping”) tasks inside the colony before switching to outside foraging at approximately 23 days old. Disease resistance is an important feature of honeybee biology, but little is known about the interaction of pathogens and age-related division of labor. We tested a hypothesis that older forager bees and younger “house” bees differ in susceptibility to infection. We coupled an infection bioassay with a functional analysis of gene expression in individual bees using a whole genome microarray. Forager bees treated with the entomopathogenic fungus Metarhizium anisopliae s.l. survived for significantly longer than house bees. This was concomitant with substantial differences in gene expression including genes associated with immune function. In house bees, infection was associated with differential expression of 35 candidate immune genes contrasted with differential expression of only two candidate immune genes in forager bees. For control bees (i.e. not treated with M. anisopliae) the development from the house to the forager stage was associated with differential expression of 49 candidate immune genes, including up-regulation of the antimicrobial peptide gene abaecin, plus major components of the Toll pathway, serine proteases, and serpins. We infer that reduced pathogen susceptibility in forager bees was associated with age-related activation of specific immune system pathways. Our findings contrast with the view that the immunocompetence in social insects declines with the onset of foraging as a result of a trade-off in the allocation of resources for foraging. The up-regulation of immune-related genes in young adult bees in response to M. anisopliae infection was an indicator of disease susceptibility; this also challenges previous research in social insects, in which an elevated immune status has been used as a marker of increased disease resistance and fitness without considering the effects of age-related development.

Honeybees have a highly developed form of social biology in which tasks are distributed among workers according to their age, with younger bees performing housekeeping tasks (“house bees”) before switching to foraging duties when they grow older. This division of labor is vital to colony function and survival. Pathogens are known to be partly responsible for the current decline in honeybee populations around the world, but we understand little about the responses of different types of worker bee to infection. In this study, we infected house and forager bees with an insect pathogen. We measured bee survival rate and the expression of genes that regulate the immune system. More immune genes were up regulated in house bees than foragers in response to infection, but foragers were more resistant to the pathogen than house bees. We found that development from the house to forager stages resulted in increased expression of genes that regulate the production of antimicrobial proteins. The inference is that parts of the immune system are activated during development, resulting in greater resistance to infectious disease in forager bees. Our study provides new insights into the functioning of the honeybee immune system and its interaction with social organisation.

Effects of tumour necrosis factor α (TNFα) on Mytilus haemocytes: role of stress-activated mitogen-activated protein kinases (MAPKs)

BACKGROUND INFORMATION

Many studies indicate that innate immunity in invertebrates can be modulated by a cytokine network like in vertebrates. In molluscs, the immune response is carried out by circulating haemocytes and soluble haemolymph factors. In the present study, the effects of heterologous TNFalpha (tumour necrosis factor alpha) on cell signalling and function in the haemocytes of the bivalve Mytilus galloprovincialis Lam. were investigated.

RESULTS AND CONCLUSIONS

Addition of TNFalpha in the absence of haemolymph serum [in ASW (artificial sea water)] induced cellular stress, as indicated by lysosomal destabilization, and decreased phagocytosis; on the other hand, in the presence of serum, TNFalpha did not affect lysosomal stability and even stimulated phagocytosis. TNFalpha induced rapid phosphorylation of the stress-activated p38 and JNK (c-Jun N-terminal kinase) MAPKs (mitogen-activated protein kinases); both effects were persistent in ASW but transient in serum. Activation of p38 and JNKs in mediating the effects of TNFalpha was confirmed by the use of specific MAPK inhibitors. Moreover, flow cytometric analysis indicated that TNFalpha in the presence of serum induced transient phosphatidylserine exposure on the haemocyte surface, evaluated as annexin V binding; in ASW, the cytokine resulted in a stable increase in the percentage of both annexin- and propidium iodide-positive cells, indicating possible apoptotic/necrotic processes. The results indicate that TNFalpha can affect the function of bivalve haemocytes through conserved transduction pathways involving stress-activated MAPKs and suggest that the haemocyte response to the cytokine is influenced by soluble haemolymph components.

Humoral immune response of Galleria mellonella larvae after infection by Beauveria bassiana under optimal and heat-shock conditions

Natural infection of Galleria mellonella larvae with the entomopathogenic fungus Beauveria bassiana led to antifungal, but not antibacterial host response. This was manifested by induction of gallerimycin and galiomicin gene expression and, consequently, the appearance of antifungal activity in the hemolymph of the infected larvae. The activity of lysozyme increased at the beginning of infection and dropped while infection progressed. Exposure of the naturally infected animals to 43 degrees C for 15 min extended their life time. Galleria mellonella larvae were injected with 10(4), 10(5) and 10(6) fungal blastospores, resulting in the appearance of strong antifungal activity and a significant increase in lysozyme activity in larval hemolymph after 24h. Antibacterial activity was detectable only when 10(5) and increased when 10(6) blastospores were injected. The number of the injected B. bassiana blastospores also determined the survival rate of animals. We found that exposure of the larvae to 38 degrees C for 30 min before infection extended their life time when 10(3) and 10(4) spores were injected. The increase in the survival rate of the pre-heat-shocked animals may be explained by higher expression of antimicrobial peptides and higher antifungal and lysozyme activities in their hemolymph in comparison to non-heat-shocked animals.

The antioxidants dimethylsulfoxide and dimethylthiourea affect the immediate adhesion responses of larval haemocytes from 3 lepidopteran insect species

Antioxidants, dimethylsulfoxide (DMSO) and dimethylthiourea (DMTU), at concentrations not affecting the viability of blood cells (haemocytes) from the larval stage of 3 lepidopteran insects - Galleria mellonella, Lymantria dispar, and Malacosoma disstria - differed in their influence on the innate binding of haemocytes to glass, bacteria to haemocytes, and on humoral responses to alien materials. In vitro DMSO had little effect, whereas DMTU substantially impaired the adhesion of the haemocyte types, the plasmatocytes and granular cells, to slides as well as the attachment of Bacillus subtilis to these haemocytes. Although both antioxidants increased lysozyme and phenoloxidase activities, there was no correlation of enzyme activity and haemocyte adhesion responses, possibly reflecting sequestered radicals. Nitric oxide and hydroxyl radicals offset the DMTU effect. In the absence of antioxidants, inactivate protein kinases A (PKA) and C (PKC) enhanced haemocyte aggregation. In general, DMSO, as opposed to DMTU, did not alter the effects of PKA and PKC activators and inhibitors on haemocyte aggregation or of PKC and PKA activities. High concentrations of DMSO and all levels of DMTU, although inhibiting PKA and PKC, inhibited haemocyte adhesion to slides. Comparable results occurred for DMTU-treated haemocytes incubated with B. subtilis. In vivo DMSO, unlike DMTU, did not impair plasmatocyte or granular cell responses to foreign materials, including bacterial removal from the haemolymph and nodulation.

Humoral immune response upon mild heat-shock conditions in Galleria mellonella larvae

Larvae of Galleria mellonella exposed to mild heat-shock (38 degrees C) showed an enhanced humoral immune response after microbial infection in comparison to infected animals grown at 28 degrees C. This enhanced response was manifested by increased expression of antimicrobial peptide (AMP) genes leading to enhanced antimicrobial activity in the hemolymph. We found an increased level of Hsp90 and changes in the level of a 55kDa protein recognized by anti-Hsp90 antibodies in fat bodies of infected animals reared at 28 degrees C as well as in uninfected animals exposed to elevated temperature. Pre-treatment of animals with an inhibitor of Hsp90, 17-DMAG, prior to immunization resulted in increased expression of AMP genes encoding gallerimycin and cecropin at 38 degrees C. This observation was correlated with the changes in Hsp90 protein and increased level of 55kDa protein. Also G. mellonella larvae pre-treated with 17-DMAG and exposed to mild heat-shock for 30min showed an increased survival rate after infection with entomopathogenic bacteria Pseudomonas aeruginosa. We also show the effect of 17-DMAG on the phosphorylation state of ERK MAP kinase. We postulate that Hsp90 may play a significant role in converging pathways involved in the insect immune response and heat-shock.

Modulation of iridovirus-induced apoptosis by endocytosis, early expression, JNK, and apical caspase

Chilo iridescent virus (CIV) is the type species for the family Iridoviridae, which are large, isometric, cytoplasmic dsDNA viruses. We examined the mechanism of apoptosis induction by CIV. High CIV doses (CIV_XS; 400 μg/ml), UV-irradiated virus (CIV_UV; 10 μg/ml) and CVPE (CIV protein extract; 10 μg/ml) induced apoptosis in 60% of treated Choristoneura fumiferana (IPRI-CF-124T) cells. Normal doses of infectious CIV (10 μg/ml) induced apoptosis in only 10% of C. fumiferana (CF) cells. Apoptosis was inhibited by Z-IETD-FMK, an apical caspase inhibitor, indicating that CIV-induced apoptosis requires caspase activity. The putative caspase in CF cells was designated Cf-caspase-i. CIV_UV or CVPE enhanced Cf-caspase-i activity by 80% at 24 h relative to mock-treated cells. Since the MAP kinase pathway induces or inhibits apoptosis depending on the context, we used JNK inhibitor SP600125 and demonstrated drastic suppression of CVPE-induced apoptosis. Thus, the JNK signaling pathway is significant for apoptosis in this system. Virus interaction with the cell surface was not sufficient for apoptosis since CIV_UV particles bound to polysterene beads failed to induce apoptosis. Endocytosis inhibitors (bafilomycin or ammonium chloride) negated apoptosis induction by CIV_UV, CIV_XS or CVPE indicating that entry through this mode is required. Given the weak apoptotic response to infectious CIV, we postulated that viral gene expression inhibited apoptosis. CIV infection of cells pretreated with cycloheximide induced apoptosis in 69% of the cells compared to 10% in normal infections. Furthermore, blocking viral DNA replication with aphidicolin or phosphonoacetic acid suppressed apoptosis and Cf-caspase-i activity, indicating that early viral expression is necessary for inhibition of apoptosis, and de novo synthesis of viral proteins is not required for induction. We show for the first time that, in a member of the family Iridoviridae, apoptosis: (i) requires entry and endocytosis of virions or virion proteins, (ii) is inhibited under conditions permitting early viral expression, and (iii) requires the JNK signaling pathway. This is the first report of JNK signal requirement during apoptosis induction by an insect virus.

Protein kinase A activity and protein phosphorylation in the haemocytes of immune-challenged Galleria mellonella larvae

Protein kinase A (PKA) activity was detected in the haemocytes of greater wax moth, Galleria mellonella larvae using a specific peptide substrate--kemptide. The enzyme was activated in vitro by 1 microM concentration of cAMP, 8-Br-cAMP, 8-Chl-cAMP and BzcMP, whereas in the case of cGMP 10 microM concentration was necessary. Immune challenge of G. mellonella larvae with bacteria led to changes in haemocyte PKA activity. Gram-positive M. luteus was a better inducer of PKA activity than Gram-negative E. coli. The kinetics of activity changes was dependent on the bacteria used and considerably differed from that observed in water-treated insects. Inhibition of PKA activity by cell-permeable, specific inhibitor, Rp-8-Br-cAMPS, induced changes in haemocyte morphology resembling those caused by live bacteria. Four potential PKA substrates of 155 kDa, 44 kDa, 40 kDa and 22 kDa were recognized in the haemocytes of naive larvae by phospho-motif antibodies for PKA phosphorylation consensus site. The modification level of 40 kDa protein changed after water treatment and immune challenge of G. mellonella larvae, whereas that of 155 kDa protein changed only after E. coli and LPS injections. Additionally, in the haemocytes of bacteria- and LPS-challenged insects a transient phosphorylation of 36 kDa protein was detected.

Immune pathways and defence mechanisms in honey bees Apis mellifera

Social insects are able to mount both group-level and individual defences against pathogens. Here we focus on individual defences, by presenting a genome-wide analysis of immunity in a social insect, the honey bee Apis mellifera. We present honey bee models for each of four signalling pathways associated with immunity, identifying plausible orthologues for nearly all predicted pathway members. When compared to the sequenced Drosophila and Anopheles genomes, honey bees possess roughly one-third as many genes in 17 gene families implicated in insect immunity. We suggest that an implied reduction in immune flexibility in bees reflects either the strength of social barriers to disease, or a tendency for bees to be attacked by a limited set of highly coevolved pathogens.

Studies on the role of protein kinase A in humoral immune response of Galleria mellonella larvae

Protein kinase A (PKA) activity was detected in the fat body of Galleria mellonella larvae by a non-radioactive method using a specific peptide substrate-kemptide. The enzyme activity was stimulated by cAMP and its analogues: BzcMP, 8-Chl-cAMP and 8-Br-cAMP in concentrations of 1-4muM. Cyclic GMP was not effective in PKA activation. A two-fold increase in PKA activity was detected in the fat body of G. mellonella LPS-challenged larvae. Selective, membrane-permeable PKA inhibitors, H89 and Rp-8-Br-cAMPS, inhibited protein kinase A activity in the fat body of G. mellonella larvae in vitro and in vivo. The inhibition of PKA activity in vivo was correlated with a considerable lowering of haemolymph antibacterial activity and a decrease in lysozyme content in the fat body of immune challenged larvae. The use of phospho-motif antibodies recognising PKA phosphorylation consensus site allowed identification of four potential PKA phosphorylation substrates of 79, 45, 40 and 36kDa in G. mellonella fat body.