Antimicrobial peptide defense in Drosophila

Blap-6, a Novel Antifungal Peptide from the Chinese Medicinal Beetle Blaps rhynchopetera against Cryptococcus neoformans

Cryptococcus neoformans (C. neoformans) is a pathogenic fungus that can cause life-threatening meningitis, particularly in individuals with compromised immune systems. The current standard treatment involves the combination of amphotericin B and azole drugs, but this regimen often leads to inevitable toxicity in patients. Therefore, there is an urgent need to develop new antifungal drugs with improved safety profiles. We screened antimicrobial peptides from the hemolymph transcriptome of Blaps rhynchopetera (B. rhynchopetera), a folk Chinese medicine. We found an antimicrobial peptide named blap-6 that exhibited potent activity against bacteria and fungi. Blap-6 is composed of 17 amino acids (KRCRFRIYRWGFPRRRF), and it has excellent antifungal activity against C. neoformans, with a minimum inhibitory concentration (MIC) of 0.81 μM. Blap-6 exhibits strong antifungal kinetic characteristics. Mechanistic studies revealed that blap-6 exerts its antifungal activity by penetrating and disrupting the integrity of the fungal cell membrane. In addition to its direct antifungal effect, blap-6 showed strong biofilm inhibition and scavenging activity. Notably, the peptide exhibited low hemolytic and cytotoxicity to human cells and may be a potential candidate antimicrobial drug for fungal infection caused by C. neoformans.

Ingested soil bacteria breach gut epithelia and prime systemic immunity in an insect

Insects lack acquired immunity and were thought to have no immune memory, but recent studies reported a phenomenon called immune priming, wherein sublethal dose of pathogens or nonpathogenic microbes stimulates immunity and prevents subsequential pathogen infection. Although the evidence for insect immune priming is accumulating, the underlying mechanisms are still unclear. The bean bug Riptortus pedestris acquires its gut microbiota from ambient soil and spatially structures them into a multispecies and variable community in the anterior midgut and a specific, monospecies Caballeronia symbiont population in the posterior region. We demonstrate that a particular Burkholderia strain colonizing the anterior midgut stimulates systemic immunity by penetrating gut epithelia and migrating into the hemolymph. The activated immunity, consisting of a humoral and a cellular response, had no negative effect on the host fitness, but on the contrary protected the insect from subsequent infection by pathogenic bacteria. Interruption of contact between the Burkholderia strain and epithelia of the gut weakened the host immunity back to preinfection levels and made the insects more vulnerable to microbial infection, demonstrating that persistent acquisition of environmental bacteria is important to maintain an efficient immunity.

Sporothrix brasiliensis Infection Modulates Antimicrobial Peptides and Stress Management Gene Expression in the Invertebrate Biomodel Galleria mellonella

Sporothrix brasiliensis is the most pathogenic species, responsible for the Brazilian cat-transmitted sporotrichosis hyperendemic. In this scenario, an investigation of the pathogen-host interaction can provide relevant information for future treatment strategies. To this end, the invertebrate Galleria mellonella has proven to be a suitable alternative for evaluating the virulence of pathogenic fungi, since the insect immune system is similar to the mammalian innate immune response. The aim of this work was to investigate phenotypic and molecular aspects of the immune response of G. mellonella throughout the S. brasiliensis infection. Hemocyte density and the evolution of the fungal load were evaluated. In parallel, RT-qPCR expression analysis of genes encoding antimicrobial peptides (Gallerimycin and Galiomycin) and stress management genes (C7 Contig 15362 and C8 Contig 19101) was conducted. The fungal load and hemocyte densities increased simultaneously and proportionally to the deleterious morphological events and larvae mortality. Gallerimycin, C7 Contig 15362 and C8 Contig 19101 genes were positively regulated (p < 0.05) at distinct moments of S. brasiliensis infection, characterizing a time-dependent and alternately modulated profile. Galiomycin gene expression remained unchanged. Our results contribute to the future proposal of potential alternative pathways for treating and consequently controlling S. brasiliensis zoonosis, a major public health issue in Latin America.

Design of Potent and Salt-Insensitive Antimicrobial Branched Peptides

Dendrimeric and branched peptides are polypeptides formed by diverse types of scaffolds to give them different forms. Previously, we reported a cascade-type, Lys-scaffolded antimicrobial peptide dendrimer D4R tethered with four RLYR tetrapeptides. Antimicrobial D4R is broad-spectrum, salt insensitive, and as potent as the natural-occurring tachyplesins, displaying minimum inhibitory concentrations (MIC) < 1 μM. However, the relationships between scaffolds and antimicrobial potency remain undefined. Here, we report the design of four novel types of peptide antimicrobials whose scaffolded backbones are lysine (Lys), iso-Lys, ornithine (Orn), or iso-Orn tethered with RLYR on their α- or sidechain-amines to give ε-, δ-, and their α-branched peptides. When assayed against ten microorganisms, the Lys-scaffolded α- and ε-branched peptides are broadly active, salt insensitive, and as potent as D4R and tachyplesins, whereas the corresponding Orn-scaffolded α- and δ-branched peptides are salt sensitive and much less potent, displaying MICs ranging from 1 to >500 μM. Structure-activity relationship studies suggested that Lys-scaffolds, but not Orn-scaffolds, can support a reverse turn to organize RLYR tetrapeptides as parallel β-strands to form an amphipathic structure with Leu-Tyr as a hydrophobic core. Together, these results provide a structural approach for designing potent and salt-insensitive dendrimeric or branched peptide antimicrobials.

Blapstin, a Diapause-Specific Peptide-Like Peptide from the Chinese Medicinal Beetle Blaps rhynchopetera, Has Antifungal Function

Drug resistance against bacteria and fungi has become common in recent years, and it is urgent to discover novel antimicrobial peptides to manage this problem. Many antimicrobial peptides from insects have been reported to have antifungal activity and are candidate molecules in the treatment of human diseases. In the present study, we characterized an antifungal peptide named blapstin that was isolated from the Chinese medicinal beetle Blaps rhynchopetera used in folk medicine. The complete coding sequence was cloned from the cDNA library prepared from the midgut of B. rhynchopetera. It is a 41-amino-acid diapause-specific peptide (DSP)-like peptide stabilized by three disulfide bridges and shows antifungal activity against Candida albicans and Trichophyton rubrum with MICs of 7 μM and 5.3 μM, respectively. The C. albicans and T. rubrum treated with blapstin showed irregular and shrunken cell membranes. In addition, blapstin inhibited the activity of C. albicans biofilm and showed little hemolytic or toxic activity on human cells and it is highly expressed in the fat body, followed by the hemolymph, midgut, muscle, and defensive glands. These results indicate that blapstin may help insects fight against fungi and showed a potential application in the development of antifungal reagents. IMPORTANCE Candida albicans is one of the conditional pathogenic fungi causing severe nosocomial infections. Trichophyton rubrum and other skin fungi are the main pathogens of superficial cutaneous fungal diseases, especially in children and the elderly. At present, antibiotics such as amphotericin B, ketoconazole, and fluconazole are the main drugs for the clinical treatment of C. albicans and T. rubrum infections. However, these drugs have certain acute toxicity. Long-term use can increase kidney damage and other side effects. Therefore, obtaining broad-spectrum antifungal drugs with high efficiency and low toxicity for the treatment of C. albicans and T. rubrum infections is a top priority. Blapstin is an antifungal peptide which shows activity against C. albicans and T. rubrum. The discovery of blapstin provides a novel clue for our understanding of the innate immunity of Blaps rhynchopetera and provides a template for designing antifungal drugs.

Can immune gene silencing via dsRNA feeding promote pathogenic viruses to control the globally invasive Argentine ant?

Pest control methods that can target pest species with limited environmental impacts are a conservation and economic priority. Species-specific pest control using RNA interference is a challenging but promising avenue in developing the next generation of pest management. We investigate the feasibility of manipulating a biological invader's immune system using double-stranded RNA (dsRNA) in order to increase susceptibility to naturally occurring pathogens. We used the invasive Argentine ant as a model, targeting the immunity-associated genes Spaetzle and Dicer-1 with dsRNA. We show that feeding with Spaetzle dsRNA can result in partial target gene silencing for up to 28 days in the laboratory and 5 days in the field. Dicer-1 dsRNA only resulted in partial gene knockdown after 2 days in the laboratory. Double-stranded RNA treatments were associated with significant gene expression disruptions across immune pathways in the laboratory and to a lower extent in the field. In total, 12 viruses and four bacteria were found in these ant populations. Some changes in viral loads in dsRNA-treated groups were observed. For example, Linepithema humile Polycipivirus 2 (LhuPCV2) loads increased after 2 days of treatment with Spaetzle and Dicer-1 dsRNA treatments in the laboratory. After treatment with the dsRNA in the field, after 5 days the virus Linepithema humile toti-like virus 1 (LhuTLV1) was significantly more abundant. However, immune pathway disruption did not result in a consistent increase in microbial infections, nor did it alter ant abundance in the field. Some viruses even declined in abundance after dsRNA treatment. Our study explored the feasibility of lowering a pest's immunity as a control tool. We demonstrate that it is possible to alter immune gene expression of pest species and pathogen loads, although in our specific system the affected pathogens did not appear to influence pest abundance. We provide suggestions on future directions for dsRNA-mediated immune disruption in pest species, including potential avenues to improve dsRNA delivery as well as the importance of pest and pathogen biology. Double-stranded RNA targeting immune function might be especially useful for pest control in systems in which viruses or other microorganisms are prevalent and have the potential to be pathogenic.

Toll signal pathway activating eicosanoid biosynthesis shares its conserved upstream recognition components in a lepidopteran Spodoptera exigua upon infection by Metarhizium rileyi, an entomopathogenic fungus

Eicosanoids play crucial roles in mediating immune responses in insects. Upon a fungal infection, Toll signal pathway can mediate immune responses of Spodoptera exigua, a lepidopteran insect, by activating eicosanoid biosynthesis. However, upstream signal components of the Toll signal pathway activating eicosanoid biosynthesis remain unclear. This study predicted pattern recognition receptors (PRRs) and serine proteases (SPs) as upstream components of the Toll pathway with reference to known signal components of Manduca sexta, another lepidopteran insect. S. exigua infected with Metarhizium rileyi, an entomopathogenic fungus, activated phospholipase A₂ (PLA₂) and phenoloxidase (PO) enzymes along with marked increases of expression levels of genes encoding three specific antimicrobial peptides, cecropin, gallerimycin, and hemolin. Among ten Toll receptors encoded in the genome of S. exigua, seven Toll genes were associated with immune responses against fungal infection by M. rileyi through individual RNA interference (RNAi) screening. In addition, two Spätzles (ligands of Toll receptor) were required for Toll signaling against the fungal infection. All predicted upstream components of the Toll pathway were inducible by the fungal infection. Individual RNAi screening showed that three PRRs (βGRP-1, βGRP-2, and GNBP3) and five SPs (ModSP, HP21, HP5, HP6, and HP8) were required for immune responses of S. exigua mediated by Toll signal pathway against the fungal infection. However, two PO-activating proteases (PAP1 and PAP3) were not required for PLA₂ activation, although they were required for PO activation. These results suggest that PRRs and SPs conserved as upstream components in Toll signal pathway play crucial roles in triggering eicosanoid biosynthesis of S. exigua to mediate various immune responses against fungal infection.

Honey Bee (Apis mellifera) Immunity

At the individual level, honey bees (Apis mellifera) rely on innate immunity, which operates through cellular and humoral mechanisms, to defend themselves against infectious agents and parasites. At the colony level, honey bees have developed collective defense mechanisms against pathogens and pests, such as hygienic and grooming behaviors. An understanding of the immune responses of honey bees is critical to implement strategies to reduce mortality and increase colony productivity. The major components and mechanisms of individual and social immunity of honey bees are discussed in this review.

Effects of Local and Systemic Immune Challenges on the Expression of Selected Salivary Genes in the Malaria Mosquito Anopheles coluzzii

Salivary glands play a crucial tripartite role in mosquito physiology. First, they secrete factors that greatly facilitate both sugar and blood meal acquisition. Second, the transmission of pathogens (parasites, bacteria and viruses) to the vertebrate host requires both the recognition and invasion of the salivary glands. Third, they produce immune factors that both protect the organ from invading pathogens and are also able to exert their activity in the crop and the midgut when saliva is re-ingested during feeding. Studies on mosquito sialomes have revealed the presence of several female and/or male salivary gland-specific or enriched genes whose function is completely unknown so far. We focused our attention on these orphan genes, and we selected, according to sequence and structural features, a shortlist of 11 candidates with potential antimicrobial properties. Afterwards, using qPCR, we investigated their expression profile at 5 and 24 h after an infectious sugar meal (local challenge) or thoracic microinjection (systemic challenge) of Gram-negative (Escherichia coli, EC) or Gram-positive (Staphylococcus aureus, SA) bacteria. We observed a general increase in the transcript abundance of our salivary candidates between 5 and 24 h after local challenge. Moreover, transcriptional modulation was determined by the nature of the stimulus, with salivary gland-enriched genes (especially hyp15 upon SA stimulus) upregulated shortly after the local challenge and later after the systemic challenge. Overall, this work provides one of the first contributions to the understanding of the immune role of mosquito salivary glands. Further characterization of salivary candidates whose expression is modulated by immune challenge may help in the identification of possible novel antimicrobial peptides.

Facilitating Drug Discovery in Human Disease Models Using Insects

Drugs are developed through basic studies and clinical trials. In basic studies, researchers seek drug candidates using in vitro evaluation systems and subsequently examine their effectiveness in animal experiments as in vivo evaluations. Drug candidates identified in basic studies are tested to determine whether they are effective against human diseases in clinical trials. However, most drug candidates identified in in vitro evaluation systems do not show therapeutic effects in animal experiments due to pharmacokinetics and toxicity problems in the in vivo evaluations. This review outlines drug discovery using insect disease models that allow us to perform in vivo screening. Since insects have various advantages as experimental animals such as low cost for rearing and few ethical concerns, researchers can perform large-scale in vivo screening to find drug candidates. Silkworms are insects frequently used for studies of drug efficacy, pharmacokinetics, and toxicity. Based on silkworm research, I describe the benefits of using insect disease models for drug discovery. The use of insect disease models for in vivo screening is expected to facilitate drug discovery.

The Genetic Basis of Natural Variation in Drosophila melanogaster Immune Defense against Enterococcus faecalis

Dissecting the genetic basis of natural variation in disease response in hosts provides insights into the coevolutionary dynamics of host-pathogen interactions. Here, a genome-wide association study of Drosophila melanogaster survival after infection with the Gram-positive entomopathogenic bacterium Enterococcus faecalis is reported. There was considerable variation in defense against E. faecalis infection among inbred lines of the Drosophila Genetics Reference Panel. We identified single nucleotide polymorphisms associated with six genes with a significant (p < 10^-08, corresponding to a false discovery rate of 2.4%) association with survival, none of which were canonical immune genes. To validate the role of these genes in immune defense, their expression was knocked-down using RNAi and survival of infected hosts was followed, which confirmed a role for the genes krishah and S6k in immune defense. We further identified a putative role for the Bomanin gene BomBc1 (also known as IM23), in E. faecalis infection response. This study adds to the growing set of association studies for infection in Drosophila melanogaster and suggests that the genetic causes of variation in immune defense differ for different pathogens.

Design of Antimicrobial Peptides: Progress Made with Human Cathelicidin LL-37

The incorporation of the innate immune system into humans is essential for survival and health due to the rapid replication of invading microbes and the delayed action of the adaptive immune system. Antimicrobial peptides are important components of human innate immunity. Over 100 such peptides have been identified in various human tissues. Human cathelicidin LL-37 is best studied, and there has been a growing interest in designing new peptides based on LL-37. This chapter describes the alternative processing of the human cathelicidin precursor, protease digestion, and lab cutting of LL-37. Both a synthetic peptide library and structure-based design are utilized to identify the active regions. Although challenging, the determination of the 3D structure of LL-37 enabled the identification of the core antimicrobial region. The minimal region of LL-37 can be function-dependent. We discuss the design and potential applications of LL-37 into antibacterial, antibiofilm, antiviral, antifungal, immune modulating, and anticancer peptides. LL-37 has been engineered into 17BIPHE2, a stable, selective, and potent antimicrobial, antibiofilm, and anticancer peptide. Both 17BIPHE2 and SAAP-148 can eliminate the ESKAPE pathogens and show topical in vivo antibiofilm efficacy. Also discussed are other application strategies, including peptide formulation, antimicrobial implants, and peptide-inducing factors such as vitamin D and sunlight. Finally, we summarize what we learned from peptide design based on human LL-37.

Antimicrobial and Antibiofilm Activity of a Recombinant Fragment of β-Thymosin of Sea Urchin Paracentrotus lividus

With the aim to obtain new antimicrobials against important pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa, we focused on antimicrobial peptides (AMPs) from Echinoderms. An example of such peptides is Paracentrin 1 (SP1), a chemically synthesised peptide fragment of a sea urchin thymosin. In the present paper, we report on the biological activity of a Paracentrin 1 derivative obtained by recombination. The recombinant paracentrin RP1, in comparison to the synthetic SP1, is 22 amino acids longer and it was considerably more active against the planktonic forms of S. aureus ATCC 25923 and P. aeruginosa ATCC 15442 at concentrations of 50 µg/mL. Moreover, it was able to inhibit biofilm formation of staphylococcal and P. aeruginosa strains at concentrations equal to 5.0 and 10.7 µg/mL, respectively. Molecular dynamics (MD) simulations allowed to rationalise the results of the experimental investigations, providing atomistic insights on the binding of RP1 toward models of mammalian and bacterial cell membranes. Overall, the results obtained point out that RP1 shows a remarkable preference for bacterial membranes, in excellent agreement with the antibacterial activity, highlighting the promising potential of using the tested peptide as a template for the development of novel antimicrobial agents.

Antimicrobial Peptides and Their Therapeutic Potential for Bacterial Skin Infections and Wounds

Alarming data about increasing resistance to conventional antibiotics are reported, while at the same time the development of new antibiotics is stagnating. Skin and soft tissue infections (SSTIs) are mainly caused by the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) which belong to the most recalcitrant bacteria and are resistant to almost all common antibiotics. S. aureus and P. aeruginosa are the most frequent pathogens isolated from chronic wounds and increasing resistance to topical antibiotics has become a major issue. Therefore, new treatment options are urgently needed. In recent years, research focused on the development of synthetic antimicrobial peptides (AMPs) with lower toxicity and improved activity compared to their endogenous counterparts. AMPs appear to be promising therapeutic options for the treatment of SSTIs and wounds as they show a broad spectrum of antimicrobial activity, low resistance rates and display pivotal immunomodulatory as well as wound healing promoting activities such as induction of cell migration and proliferation and angiogenesis. In this review, we evaluate the potential of AMPs for the treatment of bacterial SSTIs and wounds and provide an overview of the mechanisms of actions of AMPs that contribute to combat skin infections and to improve wound healing. Bacteria growing in biofilms are more resistant to conventional antibiotics than their planktonic counterparts due to limited biofilm penetration and distinct metabolic and physiological functions, and often result in chronification of infections and wounds. Thus, we further discuss the feasibility of AMPs as anti-biofilm agents. Finally, we highlight perspectives for future therapies and which issues remain to bring AMPs successfully to the market.

Interorgan Molecular Communication Strategies of "Local" and "Systemic" Innate Immune Responses in Mosquito Anopheles stephensi

Mosquitoes that transmit many deadly infectious diseases also need to keep fighting against many microbial infections. Constitutive expression of multiple antimicrobial peptides (AMPs) in almost all body tissues is believed to facilitate the effective management of these local infections. When any infection breaches the local barrier, AMPs are induced rapidly in non-target tissues such as hemocytes (HCs) and establish their co-ordination with systemic immune effectors to clear off the body infection. But how interorgan immune communication is managed during local and systemic infections remain largely unknown. To understand this interorgan molecular relationship, we identified, extensively profiled and compared the expression of AMPs in three important mosquito tissues viz. midgut, fat body (FB), and HCs. dsRNA-mediated AMPs silencing suggests that mosquito tissues are able to manage an optimal expression of AMPs at the physiological level. We also examined the possible contribution of two important immune regulator genes relish (REL) and nitric oxide synthase, controlling AMPs expression in these tissues during local or systemic infections. We show that each tissue has a unique ability to respond to local/systemic challenges, but HCs are more specialized to recognize and discriminate-specific antigens than gut and FB. Our investigation also revealed that both REL and NO participate in the overall management of the interorgan immune responses, but at the same time each tissue also has its own ability to maintain the interorgan flow of signals. In our knowledge, this is the first large-scale study examining the interorgan immune relationship in the mosquito.

Regulation of Antimicrobial Peptides in Aedes aegypti Aag2 Cells

Antimicrobial peptides (AMPs) are an important group of immune effectors that play a role in combating microbial infections in invertebrates. Most of the current information on the regulation of insect AMPs in microbial infection have been gained from Drosophila, and their regulation in other insects are still not completely understood. Here, we generated an AMP induction profile in response to infections with some Gram-negative, -positive bacteria, and fungi in Aedes aegypti embryonic Aag2 cells. Most of the AMP inductions caused by the gram-negative bacteria was controlled by the Immune deficiency (Imd) pathway; nonetheless, Gambicin, an AMP gene discovered only in mosquitoes, was combinatorially regulated by the Imd, Toll and JAK-STAT pathways in the Aag2 cells. Gambicin promoter analyses including specific sequence motif deletions implicated these three pathways in Gambicin activity, as shown by a luciferase assay. Moreover, the recognition between Rel1 (refer to Dif/Dorsal in Drosophila) and STAT and their regulatory sites at the Gambicin promoter site was validated by a super-shift electrophoretic mobility shift assay (EMSA). Our study provides information that increases our understanding of the regulation of AMPs in response to microbial infections in mosquitoes. And it is a new finding that the A. aegypti AMPs are mainly regulated Imd pathway only, which is quite different from the previous understanding obtained from Drosophila.

An anionic defensin from Plutella xylostella with potential activity against Bacillus thuringiensis

Insect defensins, are cationic peptides that play an important role in immunity against microbial infection. In the present study, an anionic defensin from Plutella xylostella, (designated as PxDef) was first cloned and characterized. Amino acid sequence analysis showed that the mature peptide owned characteristic six-cysteine motifs with predicted isoelectric point of 5.57, indicating an anionic defensin. Quantitative real-time polymerase chain reaction analysis showed that PxDef was significantly induced in epidermis, fat body, midgut and hemocytes after injection of heat-inactivated Bacillus thuringiensis, while such an induction was delayed by the injection of live B. thuringiensis in the 4th instar larvae of P. xylostella. Knocking down the expression of nuclear transcription factor Dorsal in P. xylostella by RNA interference significantly decreased the mRNA level of PxDef, and increased the sensitivity of P. xylostella larvae to the infection by live B. thuringiensis. The purified recombinant mature peptide (PxDef) showed higher activity against Gram-positive bacteria, with the minimum inhibition concentrations of 1.6 and 2.6 µM against B. thuringiensis and Bacillus subtilis, respectively. To our knowledge, this is the first report about an anionic PxDef, which may play an important role in the immune system of P. xylostella against B. thuringiensis.

Label-free quantitative phosphoproteomic profiling of cellular response induced by an insect cytokine paralytic peptide

Paralytic peptide (PP) participates in diverse physiological processes as an insect cytokine, such as immunity control, paralysis induction, regulation of cell morphology and proliferation. To investigate the molecular mechanism underlying those physiological activities, we systematically investigated the global phosphorylation events in fat body of silkworm larvae induced by PP through label-free quantitative phosphoproteomics. 2534 phosphosites were finally identified, of which the phosphorylation level of 620 phosphosites on 244 proteins was significantly up-regulated and 67 phosphosites on 43 proteins was down-regulated. Among those proteins, 13 were protein kinases (PKs), 13 were transcription factors (TFs) across 10 families and 17 were metabolism related enzymes. Meanwhile, Motif-X analysis of the phosphorylation sites showed that 16 motifs are significantly enriched, including 8 novel phosphorylation motifs. In addition, KEGG and functional interacting network analysis revealed that phosphorylation cascades play the crucial regulation roles in PP-dependent signaling pathways, and highlighted the potential central position of the mitogen-activated protein kinases (MAPKs) in them. These analyses provide direct insights into the molecule mechanisms of cellular response induced by PP.

SIGNIFICANCE

PP as an insect cytokine participated in diverse functions including immunity control paralysis induction, regulation of cell morphology and proliferation. In this study, we performed firstly a label-free quantitative phosphoproteomics analysis. We found some new phosphorylation targets of PP-stimulation. Meanwhile, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and functional networks revealed that phosphorylation cascades play the crucial regulation roles in PP-dependent signaling pathways. In addition, the potential central position of the mitogen-activated protein kinases (MAPKs) was highlighted in PP-dependent signaling pathways. We think our findings may help us gain a systematic understanding of the cytokine-dependent response regulation in insects.

Linking Measures of Colony and Individual Honey Bee Health to Survival among Apiaries Exposed to Varying Agricultural Land Use

We previously characterized and quantified the influence of land use on survival and productivity of colonies positioned in six apiaries and found that colonies in apiaries surrounded by more land in uncultivated forage experienced greater annual survival, and generally more honey production. Here, detailed metrics of honey bee health were assessed over three years in colonies positioned in the same six apiaries. The colonies were located in North Dakota during the summer months and were transported to California for almond pollination every winter. Our aim was to identify relationships among measures of colony and individual bee health that impacted and predicted overwintering survival of colonies. We tested the hypothesis that colonies in apiaries surrounded by more favorable land use conditions would experience improved health. We modeled colony and individual bee health indices at a critical time point (autumn, prior to overwintering) and related them to eventual spring survival for California almond pollination. Colony measures that predicted overwintering apiary survival included the amount of pollen collected, brood production, and Varroa destructor mite levels. At the individual bee level, expression of vitellogenin, defensin1, and lysozyme2 were important markers of overwinter survival. This study is a novel first step toward identifying pertinent physiological responses in honey bees that result from their positioning near varying landscape features in intensive agricultural environments.

GNBP domain of Anopheles darlingi: are polymorphic inversions and gene variation related to adaptive evolution?

Anopheles darlingi is the main malaria vector in humans in South America. In the Amazon basin, it lives along the banks of rivers and lakes, which responds to the annual hydrological cycle (dry season and rainy season). In these breeding sites, the larvae of this mosquito feed on decomposing organic and microorganisms, which can be pathogenic and trigger the activation of innate immune system pathways, such as proteins Gram-negative binding protein (GNBP). Such environmental changes affect the occurrence of polymorphic inversions especially at the heterozygote frequency, which confer adaptative advantage compared to homozygous inversions. We mapped the GNBP probe to the An. darlingi 2Rd inversion by fluorescent in situ hybridization (FISH), which was a good indicator of the GNBP immune response related to the chromosomal polymorphic inversions and adaptative evolution. To better understand the evolutionary relations and time of divergence of the GNBP of An. darlingi, we compared it with nine other mosquito GNBPs. The results of the phylogenetic analysis of the GNBP sequence between the species of mosquitoes demonstrated three clades. Clade I and II included the GNBPB5 sequence, and clade III the sequence of GNBPB1. Most of these sequences of GNBP analyzed were homologous with that of subfamily B, including that of An. gambiae (87 %), therefore suggesting that GNBP of An. darling belongs to subfamily B. This work helps us understand the role of inversion polymorphism in evolution of An. darlingi.

Characterization of the effect of Cr(VI) on humoral innate immunity using Drosophila melanogaster

With the advancement of human race, different anthropogenic activities have heaped the environment with chemicals that can cause alteration in the immune system of exposed organism. As a first line of barrier, the evolutionary conserved innate immunity is crucial for the health of an organism. However, there is paucity of information regarding in vivo assessment of the effect of environmental chemicals on innate immunity. Therefore, we examined the effect of a widely used environmental chemical, Cr(VI), on humoral innate immune response using Drosophila melanogaster. The adverse effect of Cr(VI) on host humoral response was characterized by decreased gene expression of antimicrobial peptides (AMPs) in the exposed organism. Concurrently, a significantly decreased transcription of humoral pathway receptors (Toll and PGRP) and triglyceride level along with inhibition of antioxidant enzyme activities were observed in exposed organism. This in turn weakened the immune response of exposed organism that was manifested by their reduced resistance against bacterial infection. In addition, overexpression of the components of humoral immunity particularly Diptericin benefits Drosophila from Cr(VI)-induced humoral immune-suppressive effect. To our knowledge, this is the first report regarding negative impact of an environmental chemical on humoral innate immune response of Drosophila along with subsequent protection by AMPs, which may provide novel insight into host-chemical interactions. Also, our data validate the utility and sensitivity of Drosophila as a model that could be used for screening the possible risk of environmental chemicals on innate immunity with minimum ethical concern that can be further extrapolated to higher organisms.

Early Vertebrate Evolution of the Host Restriction Factor Tetherin

Tetherin is an interferon-inducible restriction factor targeting a broad range of enveloped viruses. Its antiviral activity depends on an unusual topology comprising an N-terminal transmembrane domain (TMD) followed by an extracellular coiled-coil region and a C-terminal glycosylphosphatidylinositol (GPI) anchor. One of the two membrane anchors is inserted into assembling virions, while the other remains in the plasma membrane of the infected cell. Thus, tetherin entraps budding viruses by physically bridging viral and cellular membranes. Although tetherin restricts the release of a large variety of diverse human and animal viruses, only mammalian orthologs have been described to date. Here, we examined the evolutionary origin of this protein and demonstrate that tetherin orthologs are also found in fish, reptiles, and birds. Notably, alligator tetherin efficiently blocks the release of retroviral particles. Thus, tetherin emerged early during vertebrate evolution and acquired its antiviral activity before the mammal/reptile divergence. Although there is only limited sequence homology, all orthologs share the typical topology. Two unrelated proteins of the slime mold Dictyostelium discoideum also adopt a tetherin-like configuration with an N-terminal TMD and a C-terminal GPI anchor. However, these proteins showed no evidence for convergent evolution and failed to inhibit virion release. In summary, our findings demonstrate that tetherin emerged at least 450 million years ago and is more widespread than previously anticipated. The early evolution of antiviral activity together with the high topology conservation but low sequence homology suggests that restriction of virus release is the primary function of tetherin.

IMPORTANCE

The continuous arms race with viruses has driven the evolution of a variety of cell-intrinsic immunity factors that inhibit different steps of the viral replication cycle. One of these restriction factors, tetherin, inhibits the release of newly formed progeny virions from infected cells. Although tetherin targets a broad range of enveloped viruses, including retro-, filo-, herpes-, and arenaviruses, the evolutionary origin of this restriction factor and its antiviral activity remained obscure. Here, we examined diverse vertebrate genomes for genes encoding cellular proteins that share with tetherin the highly unusual combination of an N-terminal transmembrane domain and a C-terminal glycosylphosphatidylinositol anchor. We show that tetherin orthologs are found in fish, reptiles, and birds and demonstrate that alligator tetherin efficiently inhibits the release of retroviral particles. Our findings identify tetherin as an evolutionarily ancient restriction factor and provide new important insights into the continuous arms race between viruses and their hosts.

Effect of an immune challenge on the functional performance of male weaponry

Theories of parasite-mediated sexual selection predict a positive association between immune function and the expression of sexually selected ornaments. Few studies, however, have investigated how an immune challenge affects the performance of sexually selected weaponry. Male Wellington tree weta (Hemideina crassidens) (Orthoptera: Anostostomatidae) possess enlarged mandibles that are used as weapons in fights for access to females residing in tree galleries. Intense sexual competition appears to have favoured the evolution of alternative male mating strategies in this species as males have a trimorphic phenotype in which weapon size varies across morphotype: 8th instar males have the smallest jaws, 10th instar males have the largest and 9th instar males being intermediate to the other two. After injecting males and females with either lipopolysaccharide (LPS; immune challenge) or saline (control) I measured over a 24h period each weta's body mass to assess whether they responded immunologically to the LPS and their bite force to assess the functional performance of their jaws. Both sexes responded immunologically to the immune-challenge as LPS-injected individuals lost significantly more body mass than saline-injected controls with females losing more mass than males. Female bite force was significantly reduced 8h after LPS-injection whereas male bite force did not significantly decline. Both sexes regained pre-injection functional performance of their jaws 24h after the immune challenge. My results suggest that females trade-off bite force for immune function whereas males do not. This article is part of a Special Issue entitled: insert SI title.

The damage threshold hypothesis and the immune strategies of insects

The insect immune response strategy has generally been considered bipolar: either resistance or death. Lately, a much broader and subtler landscape has emerged: occurrence of tolerance and resistance has been described as a host-regulated immune response. However, little is known about the interplay between the immune response strategy mounted by the insect during infection and the damage produced by the pathogen. Based on the Matzinger model of danger/damage, we propose a quantitative model to explain the occurrence of either resistance or tolerance. We discuss the features to be analyzed and describe the terms of reference by which, with basic models, we distinguish between immune strategies. Pathogen type and mixed infections are also contemplated. We hope this analysis will give new perspective, from an evolutionary ecology standpoint, on immune response measurements in the context of insect infection, and on the importance of (non-self or self) damage.

Immunoglobulin superfamily protein Dscam exhibited molecular diversity by alternative splicing in hemocytes of crustacean, Eriocheir sinensis

Be absent of adaptive immunity which have both specificity and memory, invertebrates seem to have evolved alternative adaptive immune strategies to resist various intruding pathogens. Whereas vertebrates could generate a wide range of immunological receptors with somatic rearrangement, invertebrates possibly depend on alternative splicing of pattern-recognition receptors (PRRs). Recently, it has been suggested that a member of the immunoglobulin superfamily (IgSF), Down syndrome cell adhesion molecule (Dscam), plays a crucial role in the alternative adaptive immune system of invertebrates. At present, we successfully isolated and characterized the first crab Dscam from Eriocheir sinensis. EsDscam has typical domain architecture compared with other Dscam orthologs, including one signal-peptide, 10 immunoglobulin (Ig) domains, 6 fibronectin type III domains (FNIII), one transmembrane domain (TM) and one cytoplasmic tail. We had detected four hypervariable regions of EsDscam in the N-terminal halves of Ig2 (25) and Ig3 domain (30), the complete Ig7 (18) and also the transmembrane domain (2), potentially generate 27,000 unique isoforms at least. Transcription of EsDscam were both a) detected in all tissues, especially in immune system, digestive system and nerve system; b) significantly induced in hemocytes post lipopolysaccharides (LPS), peptidoglycans (PG) and β-1, 3-glucans (Glu) injection. Importantly, we had detected membrane-bound and secreted Dscam isoforms in E. sinensis, and showed that secreted isoforms were extensively transcribed post different PAMPs challenge respectively. Results from immuno-localization assay revealed that EsDscam evenly distributed in the cell surface of hemocytes. These findings indicated that EsDscam is a hypervariable PRR in the innate immune system of the E. sinensis.

Immune Signaling and Antimicrobial Peptide Expression in Lepidoptera

Many lepidopteran insects are agricultural pests that affect stored grains, food and fiber crops. These insects have negative ecological and economic impacts since they lower crop yield, and pesticides are expensive and can have off-target effects on beneficial arthropods. A better understanding of lepidopteran immunity will aid in identifying new targets for the development of specific insect pest management compounds. A fundamental aspect of immunity, and therefore a logical target for control, is the induction of antimicrobial peptide (AMP) expression. These peptides insert into and disrupt microbial membranes, thereby promoting pathogen clearance and insect survival. Pathways leading to AMP expression have been extensively studied in the dipteran Drosophila melanogaster. However, Diptera are an important group of pollinators and pest management strategies that target their immune systems is not recommended. Recent advances have facilitated investigation of lepidopteran immunity, revealing both conserved and derived characteristics. Although the general pathways leading to AMP expression are conserved, specific components of these pathways, such as recognition proteins have diverged. In this review we highlight how such comparative immunology could aid in developing pest management strategies that are specific to agricultural insect pests.

Toll-like receptor regulation of effector T lymphocyte function

The landmark discovery of pattern-recognition receptors, including Toll-like receptors (TLRs), furthered our understanding on how the host rapidly responds to invading pathogens. For over a decade now, extensive research has demonstrated the crucial role of multiple TLRs in the detection of a broad range of molecules expressed by microbial pathogens as well as host-derived danger signals. TLR activation is the hallmark of the innate immune response. Recent evidence, however, demonstrates that cells of the adaptive immune response use these innate signaling pathways as well. This review discusses recent findings regarding TLR functionality in T lymphocytes with a specific emphasis on the promotion of T helper cell-dependent inflammation through direct TLR signaling.

Drosophila immune priming against Pseudomonas aeruginosa is short-lasting and depends on cellular and humoral immunity

Immune responses are traditionally divided into the innate and the adaptive arm, both of which are present in vertebrates, while only the innate arm is found in invertebrates. Immune priming experiments in Drosophila melanogaster and other invertebrates during the last decade have challenged this dogma, questioning the boundaries between innate and adaptive immunity. Studies on repeated inoculation of Drosophila with microbes reveal a long-lasting cellular immunity adaptation against particular microorganisms. Here we study the lasting effect of immune priming against infection with Pseudomonas aeruginosa, an opportunistic human pathogen that is lethal to the common fruit fly. Drosophila priming with heat-killed or low in virulence P. aeruginosa extends fly survival during a secondary lethal infection with a virulent strain of the same species. The protective immune response can last for more than 10 days after exposure to a persistent low-in-virulence live infection, but it is eliminated 7 days after the host is primed with heat-killed bacteria. Moreover, not only the cellular, but also the systemic NF-κB-mediated immune responses contribute to immune priming. Thus each microbe might elicit different mechanisms of immune priming that may or may not last for long.

Altered immunity in crowded locust reduced fungal (Metarhizium anisopliae) pathogenesis

The stress of living conditions, similar to infections, alters animal immunity. High population density is empirically considered to induce prophylactic immunity to reduce the infection risk, which was challenged by a model of low connectivity between infectious and susceptible individuals in crowded animals. The migratory locust, which exhibits polyphenism through gregarious and solitary phases in response to population density and displays different resistance to fungal biopesticide (Metarhizium anisopliae), was used to observe the prophylactic immunity of crowded animals. We applied an RNA-sequencing assay to investigate differential expression in fat body samples of gregarious and solitary locusts before and after infection. Solitary locusts devoted at least twice the number of genes for combating M. anisopliae infection than gregarious locusts. The transcription of immune molecules such as pattern recognition proteins, protease inhibitors, and anti-oxidation proteins, was increased in prophylactic immunity of gregarious locusts. The differentially expressed transcripts reducing gregarious locust susceptibility to M. anisopliae were confirmed at the transcriptional and translational level. Further investigation revealed that locust GNBP3 was susceptible to proteolysis while GNBP1, induced by M. anisopliae infection, resisted proteolysis. Silencing of gnbp3 by RNAi significantly shortened the life span of gregarious locusts but not solitary locusts. By contrast, gnbp1 silencing did not affect the life span of both gregarious and solitary locusts after M. anisopliae infection. Thus, the GNBP3-dependent immune responses were involved in the phenotypic resistance of gregarious locusts to fungal infection, but were redundant in solitary locusts. Our results indicated that gregarious locusts prophylactically activated upstream modulators of immune cascades rather than downstream effectors, preferring to quarantine rather than eliminate pathogens to conserve energy meanwhile increasing the "distance" of infectious and target individuals. Our study has obvious implications for bio-pesticides management of crowded pests, and for understanding disease epidemics and adaptiveness of pathogens.

cDNA cloning and characterization of the antibacterial peptide cecropin 1 from the diamondback moth, Plutella xylostella L

Cecropins are linear cationic antibacterial peptides that have potent activities against microorganisms. In the present study, a 480bp full-length cDNA encoding diamondback moth (Plutella xylostella) cecropin 1 (designated as Px-cec1) was obtained using RT-PCR. A Northern blot analysis showed that the Px-cec1 transcript was predominantly expressed in fat bodies, hemocytes, midgut and epidermis with the highest expression level in fat bodies. The expression of Px-cec1 mRNA in fat bodies was significantly increased 24h after microbial challenge, with the highest induced expression by Staphylococcus aureus. A circular dichroism (CD) analysis revealed that the recombinant Px-cec1 mainly contained α-helixes. Antimicrobial assays demonstrated that recombinant Px-cec1 exhibited a broad spectrum of anti-microbial properties against fungi, Gram-positive and Gram-negative bacteria, but it did not exhibit hemolytic activity against human erythrocytes. Furthermore, Px-cec1 caused significant morphological alterations of S. aureus, as shown by scanning electron microscopy and transmission electron microscopy. These results demonstrated that Px-cec1 exerts its antibacterial activity by acting on the cell membrane to disrupt bacterial cell structures.

Proteomic analysis of Frankliniella occidentalis and differentially expressed proteins in response to tomato spotted wilt virus infection

Tomato spotted wilt virus (TSWV) is transmitted by Frankliniella occidentalis in a persistent propagative manner. Despite the extensive replication of TSWV in midgut and salivary glands, there is little to no pathogenic effect on F. occidentalis. We hypothesize that the first-instar larva (L1) of F. occidentalis mounts a response to TSWV that protects it from pathogenic effects caused by virus infection and replication in various insect tissues. A partial thrips transcriptome was generated using 454-Titanium sequencing of cDNA generated from F. occidentalis exposed to TSWV. Using these sequences, the L1 thrips proteome that resolved on a two-dimensional gel was characterized. Forty-seven percent of the resolved protein spots were identified using the thrips transcriptome. Real-time quantitative reverse transcriptase PCR (RT-PCR) analysis of virus titer in L1 thrips revealed a significant increase in the normalized abundance of TSWV nucleocapsid RNA from 2 to 21 h after a 3-h acquisition access period on virus-infected plant tissue, indicative of infection and accumulation of virus. We compared the proteomes of infected and noninfected L1s to identify proteins that display differential abundances in response to virus. Using four biological replicates, 26 spots containing 37 proteins were significantly altered in response to TSWV. Gene ontology assignments for 32 of these proteins revealed biological roles associated with the infection cycle of other plant- and animal-infecting viruses and antiviral defense responses. Our findings support the hypothesis that L1 thrips display a complex reaction to TSWV infection and provide new insights toward unraveling the molecular basis of this interaction.

Legionella pneumophila pathogenesis in the Galleria mellonella infection model

Legionella pneumophila is a facultative intracellular human pathogen and the etiological agent of severe pneumonia known as Legionnaires' disease. Its virulence depends on protein secretion systems, in particular, the Dot/Icm type IV secretion system (T4SS), which is essential to establish a replication-permissive vacuole in macrophages. The analysis of the role of these systems and their substrates for pathogenesis requires easy-to-use models which approximate human infection. We examined the effectiveness of the larvae of the wax moth Galleria mellonella as a new model for L. pneumophila infection. We found that the L. pneumophila strains 130b, Paris, and JR32 caused mortality of the G. mellonella larvae that was strain, infectious dose, growth phase, and T4SS dependent. Wild-type L. pneumophila persisted and replicated within the larvae, whereas T4SS mutants were rapidly cleared. L. pneumophila strain Lp02, which is attenuated in the absence of thymidine but has a functional T4SS, resisted clearance in G. mellonella up to 18 h postinfection without inducing mortality. Immunofluorescence and transmission electron microscopy revealed that L. pneumophila resided within insect hemocytes in a vacuole that ultrastructurally resembled the Legionella-containing vacuole (LCV) observed in macrophages. The vacuole was decorated with the T4SS effector and LCV marker SidC. Infection caused severe damage to the insect organs and triggered immune responses, including activation of the phenoloxidase cascade leading to melanization, nodule formation, and upregulation of antimicrobial peptides. Taken together, these results suggest that G. mellonella provides an effective model to investigate the interaction between L. pneumophila and the host.

Systems behavior: of male courtship, the nervous system and beyond in Drosophila

Male courtship in fruit flies is regulated by the same major regulatory genes that also determine general sexual differentiation of the animal. Elaborate genetics has given us insight into the roles of these master genes. These findings have suggested two separate and independent pathways for the regulation of sexual behavior and other aspects of sexual differentiation. Only recently have molecular studies started to look at the downstream effector genes and how they might control sex-specific behavior. These studies have confirmed the essential role of the previously identified male specific products of the fruitless gene in the neuronal circuits in which it is expressed. But there is increasing evidence that a number of non-neuronal tissues and pathways play a pivotal role in modulating this circuit and assuring efficient courtship.

Molecular evolution of the cecropin multigene family in silkworm Bombyx mori

Cecropins constitute one of the largest and most potent immune protein families found in insect species with diversified numbers and features. In view of the large number of cecropin proteins existing with much sequence variations among them, an overview of the multigene cecropin family in silkworm Bombyx mori was attempted in this study. Cecropin encodes an inducible 64 residue anti-bacterial peptide and was clustered into two groups; first group viz. A and second group including B, D, E and Enbocin. Cecropin A consisted of two sub-groups located on chromosome number 6 of B.mori genome. Cecropin B consisted of six sub-groups, cecropin D and E of one each and Enbocin of two. The second sub-group formed in tandem array of multigene family locus over a length of 78.62 kb on chromosome number 26 in B.mori genome and was organized in positive as well as opposite orientation. The results indicated that cecropin B genes were organized in a close cluster with the intergenic sequence ranging from 1366 bp to 23526 bp. Interestingly a distantly related cecropin E was also located within the cecropin B multigene locus. Similarly distant members like cecropin D and Enbocin were also located in the 3' region of cecropin B locus. The maximum intergenic region of 23526 bp observed between Cecropin D and Enbocin indicates that the two genes were distantly evolved. The phylogenetic analysis clearly indicates a positive correlation between the clusters and physical location on the chromosome, as the length of the intergenic region plays a major role to create newer cecropin families. EST database analysis suggests that most of the cecropin A members were expressed in the microbial fat body while, the cecropin B was equally expressed in fat body and other target tissues. The signal peptides were conserved in all the twelve paralogous gene sequences.

Multipeptide precursor structure of acaloleptin A isoforms, antibacterial peptides from the Udo longicorn beetle, Acalolepta luxuriosa

We previously purified acaloleptin A1, A2, and A3, antibacterial peptides that are produced in the larval hemolymph of Acalolepta luxuriosa (Udo longicorn beetle). In this study, we performed cDNA cloning. The cDNA sequence showed a predicted acaloleptin A precursor that consisted of five acaloleptin A isoforms. Four (isoforms 1, 2, 3 and 4) of the five isoforms of the acaloleptin A precursor had high-level sequence identities with each other, but the N-terminal region of isoform 5 differed from those of the other acaloleptin A isoforms. Northern and Western blot analyses showed that acaloleptin A isoforms were mass-produced soon after bacterial inoculation. Finally, we purified isoform 5 from hemolymph of the immunized larvae. Isoform 5, unlike acaloleptin A1, A2 and A3, showed antimicrobial activities against a Gram-positive bacterium, Micrococcus luteus and a fungus, Magnaporthe grisea. These results suggest that the multipeptide structure of the acaloleptin A precursor allows A. luxuriosa high-level production of antibacterial peptides and resistance to a wide range of microorganisms.

Application of natural antimicrobials for food preservation

In this review, antimicrobials from a range of plant, animal, and microbial sources are reviewed along with their potential applications in food systems. Chemical and biochemical antimicrobial compounds derived from these natural sources and their activity against a range of pathogenic and spoilage microorganisms pertinent to food, together with their effects on food organoleptic properties, are outlined. Factors influencing the antimicrobial activity of such agents are discussed including extraction methods, molecular weight, and agent origin. These issues are considered in conjunction with the latest developments in the quantification of the minimum inhibitory (and noninhibitory) concentration of antimicrobials and/or their components. Natural antimicrobials can be used alone or in combination with other novel preservation technologies to facilitate the replacement of traditional approaches. Research priorities and future trends focusing on the impact of product formulation, intrinsic product parameters, and extrinsic storage parameters on the design of efficient food preservation systems are also presented.

Models of infectious diseases in the fruit fly Drosophila melanogaster

We examined the immune response of a fly as physicians might, by looking at the genesis of diseases caused by microorganisms. Fly infections are complex and there are few simple rules that can predict how an infected fly might fare. As we observed the finer details of the infections, we found that almost every microbe caused a different type of pathology in the fly. Two pattern recognition pathways, Toll and immune deficiency (Imd), were found to detect, and respond to, infections. The physiological response of the fly was modified further by Eiger, insulin, Wnt inhibitor of dorsal (WntD) and nitric oxide (NO) signaling. As in humans, some of the damage that occurred during the fly immune response was caused by an over-aggressive response rather than by the microbes themselves. When looking at the matrix of signaling pathways and the microbes being tested, it was immediately obvious that most of the pathways would need to be studied in more detail before defining the rules that govern their role in pathogenesis. This detailed analysis of signaling and pathogenesis has the potential to allow the fly to be used as a model patient instead of as simply an innate immune system model.

Rudra interrupts receptor signaling complexes to negatively regulate the IMD pathway

Insects rely primarily on innate immune responses to fight pathogens. In Drosophila, antimicrobial peptides are key contributors to host defense. Antimicrobial peptide gene expression is regulated by the IMD and Toll pathways. Bacterial peptidoglycans trigger these pathways, through recognition by peptidoglycan recognition proteins (PGRPs). DAP-type peptidoglycan triggers the IMD pathway via PGRP-LC and PGRP-LE, while lysine-type peptidoglycan is an agonist for the Toll pathway through PGRP-SA and PGRP-SD. Recent work has shown that the intensity and duration of the immune responses initiating with these receptors is tightly regulated at multiple levels, by a series of negative regulators. Through two-hybrid screening with PGRP-LC, we identified Rudra, a new regulator of the IMD pathway, and demonstrate that it is a critical feedback inhibitor of peptidoglycan receptor signaling. Following stimulation of the IMD pathway, rudra expression was rapidly induced. In cells, RNAi targeting of rudra caused a marked up-regulation of antimicrobial peptide gene expression. rudra mutant flies also hyper-activated antimicrobial peptide genes and were more resistant to infection with the insect pathogen Erwinia carotovora carotovora. Molecularly, Rudra was found to bind and interfere with both PGRP-LC and PGRP-LE, disrupting their signaling complex. These results show that Rudra is a critical component in a negative feedback loop, whereby immune-induced gene expression rapidly produces a potent inhibitor that binds and inhibits pattern recognition receptors.

The innate immune system controls the immediate response to infection. Innate immunity relies on germline encoded receptors, receptors that are present at birth, to recognize germs and trigger a protective response. Invertebrates (i.e., insects) rely on innate immunity to survive in microbial-rich environments, such as rotting fruit. However, uncontrolled innate immune responses are dangerous, leading to severe pathologies like sepsis, inflammatory bowel diseases, and lupus. Therefore, the intensity and duration of the innate immune response is kept in-check by multiple regulatory mechanisms. Here, we have identified a new feedback regulator of the Drosophila (the fruit fly) immune response, which we call Rudra. Using various approaches, we show that in the absence of Rudra the innate immune system is hyper-activated. This elevated immune response leads to better protection against bacterial infection. On the other hand, when present in excess, Rudra prevents the activation of the immune response. Furthermore, we show that Rudra turns off the immune response by binding to the receptors that are responsible for detecting bacteria, thereby preventing downstream responses.

The malaria vector mosquito Anopheles gambiae expresses a suite of larval-specific defensin genes

cDNAs of Anopheles gambiae Defensin 2 (AgDef2), Defensin 3 (AgDef3) and Defensin 4 (AgDef4), identified in the genome sequence, have been characterized and their expression profiles investigated. In contrast to both typical defensins and insect antimicrobial peptides generally, the newly identified defensins were not upregulated with acute-phase kinetics following immune challenge in insects or cell culture. However, mRNA abundance of AgDef2, AgDef3 and AgDef4 increased significantly during the larval stages. Promoter analysis of all three genes failed to identify putative immune response elements previously identified in other mosquito defensin genes. As previous studies failed to identify these larval-specific defensins, it seems likely that further antimicrobial peptide genes with nontypical expression profiles will be identified as more genome sequences become available.

Drosophila innate immunity and response to fungal infections

The fruit fly Drosophila melanogaster is an important model for the analysis of the interaction between host immune systems and fungal pathogens. Recent experiments have extended our understanding of the Toll-based signalling pathway critical to response to fungal infections, and identified new elements involved in cellular and humoral-based defences. The fly immune system shows remarkable sophistication in its ability to discriminate among pathogens, and the powerful genetics available to researchers studying the adult fly response, and the ability to manipulate cultured phagocytic cell lines with RNAi, are allowing researchers to dissect the molecular details of the process.

Morphological and quantitative aspects of nodule formation in hemolymph of the blowfly Chrysomya megacephala (Fabricius, 1794)

Insects manifest effective immune responses that include both cellular and humoral components. Morphological and quantitative aspects of cellular and humoral cooperation during nodule formation in Chrysomya megacephala hemolymph against Saccharomyces cerevisae yeast cells were demonstrated for the first time. The analyses were performed in non-injected larvae (NIL), saline-injected larvae (SIL) and yeast-injected larvae (YIL). The hemolymph of injected groups was collected 0.5, 1, 2, 4, 12, 24, 36, or 48-h post-injection. Morphological aspects of YIL nodulation were investigated using transmission electron microscopy (TEM). Quantitative analyses consisted of total (THC) and differential hemocyte counts (DHC) in all the groups and total yeast count (TYC) in YIL, which were performed in an improved Neubauer chamber. Nodule formation was initiated at approximately 2-h post-injection. Twelve hours after the injection, TEM revealed the presence of an amorphous membrane, at the same time that circulating hemocyte number decreased significantly contrasting the increase of yeast number. Our results showed the ability of C. megacephala hemolymph to perform humoral encapsulation when hemocyte population is insufficient to eliminate the microorganisms, warranting consideration in future investigations on the relative roles played by cellular and humoral elements of innate immunity of this calliphorid.

The role of the mannose-binding lectin in innate immunity

The innate immune system, which includes mannose-binding lectin (MBL), recognizes a broad range of molecular patterns on a broad range of infectious agents and is able to distinguish them from self. MBL is a liver-derived serum protein and is secreted into the serum, where it can activate an immune response before the induction of antigen-specific immunity. Circumstantial evidence in human populations suggests that low serum levels of MBL predispose to infection. To analyze the role of MBL in vivo, we created MBL-null mice and challenged these mice with infection under various conditions. Our results suggest that MBL plays an important role as a first-line host defense against certain infectious agents. In addition, it is likely that MBL is a key regulator of inflammation beyond expected roles in the infection.

Structure-function relationships and conformational properties of alpha-MSH(6-13) analogues with candidacidal activity

Alpha-melanocyte-stimulating hormone (alpha-MSH) is an endogenous linear tridecapeptide with potent anti-inflammatory effects. We firstly demonstrated that alpha-MSH and its C-terminal sequence Lys-Pro-Val [alpha-MSH(11-13)] have antimicrobial effects against two major and representative pathogens: Staphylococcus aureus and Candida albicans. Successively, in an attempt to improve the candidacidal activity of alpha-MSH and to better understand the peptide structure-antifungal activity relations, we have recently designed and synthesized novel peptide analogues. We focused on the sequence alpha-MSH(6-13), which contains the invariant melanocortin core sequence His-Phe-Arg-Trp (6-9) and also contains the sequence Lys-Pro-Val (11-13) important for antimicrobial activity. In that structure-activity study, we discovered several compounds that have greater candidacidal activity than alpha-MSH, among which the peptide [d-Nal-7,Phe-12]-alpha-MSH(6-13) was the most potent. Here, we report a detailed conformational analysis by spectroscopic and computational methods of three peptides, alpha-MSH(6-13) (1), [d-Nal-7,Phe-12]-alpha-MSH(6-13) (2) and [d-Nal-7,Asp-12]-alpha-MSH(6-13) (3). Peptides were chosen on the basis of their candidacidal activities and were studied in membrane mimetic environment (SDS micelles). Different turn structures were observed for the three peptides and a conformation-activity model was developed based on these results. This study offers a structural basis for the design of novel peptide and non-peptide analogues to be used as new antimicrobial agents.

Fungal Peptide Destruxin A Plays a Specific Role in Suppressing the Innate Immune Response in Drosophila melanogaster

Destruxins are a class of insecticidal, anti-viral, and phytotoxic cyclic depsipeptides that are also studied for their toxicity to cancer cells. They are produced by various fungi, and a direct relationship has been established between Destruxin production and the virulence of the entomopathogen Metarhizium anisopliae. Aside from opening calcium channels, their in vivo mode of action during pathogenesis remains largely uncharacterized. To better understand the effects of a Destruxin, we looked at changes in gene expression following injection of Destruxin A into the fruit fly Drosophila melanogaster. Microarray results revealed reduced expression of various antimicrobial peptides that play a major role in the humoral immune response of the fly. Flies co-injected with a non-lethal dose of Destruxin A and the normally innocuous Gram-negative bacteria Escherichia coli, showed increased mortality and an accompanying increase in bacterial titers. Mortality due to sepsis was rescued through ectopic activation of components in the IMD pathway, one of two signal transduction pathways that are responsible for antimicrobial peptide induction. These results demonstrate a novel role for Destruxin A in specific suppression of the humoral immune response in insects.

Antibacterial peptides in hemocytes and hematopoietic tissue from freshwater crayfish Pacifastacus leniusculus: characterization and expression pattern

A 14 amino acid residues proline/arginine-rich antibacterial peptide designated as astacidin 2 was purified and characterized from hemocytes of the freshwater crayfish, Pacifastacus leniusculus. Astacidin 2 has a broad range of antibacterial activity against both Gram-positive and Gram-negative bacteria. The primary sequence of astacidin 2 is RPRPNYRPRPIYRP with an amidated C-terminal and the molecular mass is 1838Da determined by mass spectrometry. Furthermore, the cDNA of three different crustin antibacterial homologs were isolated from a crayfish hemocyte EST library. RT-PCR was used to analyze the expression of the genes coding for astacidin 2 and P. leniusculus crustins (Plcrustin) 1-3 after bacterial challenge. The expression of Plcrustin1 was upregulated in both hemocytes and hematopoietic tissue after challenge with Gram-negative Escherichia coli or Acinetobacter ssp. non pathogenic bacteria as well as by a Gram negative crayfish pathogenic bacterium (Aeromonas hydrophila). The PlCrustin3 transcript was only upregulated after inoculation with the non-pathogenic Acinetobacter ssp. while there was no change in expression of Plcrustin2 or astacidin 2 following a bacterial challenge.