Gram-negative bacteria-binding protein, a pattern recognition receptor for lipopolysaccharide and beta-1,3-glucan that mediates the signaling for the induction of innate immune genes in Drosophila melanogaster cells

Comparison of the effect of bacterial stimulation on the global epigenetic landscape and transcription of immune genes in primarily zoophilic members of the Anopheles gambiae complex (Diptera: Culicidae)

Members of the Anopheles gambiae complex vary in their vector competence, and this is often attributed to behavioural differences. Similarly, there are differences in transmission capabilities of the zoophilic members of this complex despite exhibiting similar behaviours. Therefore, behavioural differences alone cannot fully explain vector competence variation within members of the An. gambiae complex. The immune system of mosquitoes plays a key role in determining susceptibility to parasite infection and consequently transmission capacity. This study aimed to examine variations in the immune response of An. arabiensis, An. merus and An. quadriannulatus, a major, minor, and non-vector respectively. The global epigenetic landscape was characterised and the expression of Defensin-1 and Gambicin was assessed in response to Gram-positive (Streptococcus pyogenes) and Gram-negative (Escherichia coli) bacterial infections. The effect of insecticide resistance in An. arabiensis on these aspects was also assessed. The immune system was stimulated by a blood-borne bacterial supplementation. The 5mC, 5hmC, m6A methylation levels and Histone Acetyl Transferase activity were assessed with commercial ELISA kits. The transcript levels of Defensin-1 and Gambicin were assessed by quantitative Real-Time Polymerase Chain Reaction. Species-specific differences in 5mC and m6A methylation existed both constitutively as well as post immune stimulation. The epigenetic patterns observed in the laboratory strains were largely conserved in F1 offspring of wild-caught adults. The methylation patterns in the major vector typically differed from that of the minor/non-vectors. The differences between insecticide susceptible and resistant An. arabiensis were more reflected in the expression of Defensin-1 and Gambicin. The expression of these peptides differed in the strains only after bacterial stimulation. Anopheles merus and An. quadriannulatus expressed significantly higher levels of antimicrobial peptides, both constitutively and after immune stimulation. These findings suggest molecular variations in the immune response of members of the An. gambiae complex.

The STING-mediated antiviral effect of fucoidan from Durvillaea antarctica

Fucoidans have attracted increasing attention due to their minimal toxicity and various biological activities, such as antioxidant, anti-inflammatory, anti-tumor and immunomodulatory effects. In this study, the antiviral effect and mechanism of fucoidan (FU) derived from Durvillaea antarctica were explored in vitro. The results demonstrated that FU effectively inhibited the infection of both RNA virus (VSV) and DNA virus (HSV-1). The potential antiviral mechanism of FU is to trigger the production of type I IFN (IFN-I) and IFN-stimulated genes dependent on the cytoplasmic DNA adaptor STING (stimulator of interferon genes), and to enhance innate immune response via activating the STING-TBK1-IRF3 pathway. FU possesses the potential to be an antiviral and immunomodulatory agent in the future.

Silencing gram-negative bacteria binding protein 1 decreases the immunity of Tribolium castaneum against bacteria

Gram-negative bacteria binding proteins (GNBPs) have the ability to recognize molecular patterns associated with microbial pathogens (PAMPs), leading to the activation of immune responses downstream. In the genome of Tribolium castaneum, three GNBP genes have been identified; however, their immunological roles remain unexplored. In our study, a GNBP1, designated as TcGNBP1, were identified from the cDNA library of T. castaneum. The coding sequence of TcGNBP1 consisted of 1137 bps and resulted in the synthesis of a protein comprising 378 amino acids. This protein encompasses a signal peptide, a low-complexity region, and a glycoside hydrolase 16 domain. TcGNBP1 was strongly expressed in early adult stages, and mainly distributed in hemolymph and gut. Upon being challenged with Escherichia coli or Staphylococcus aureus, the transcript levels of TcGNBP1 were significantly changed at different time points. Through molecular docking and ELISA analysis, it was observed that TcGNBP1 has the ability to interact with lipopolysaccharides, peptidoglycan, and β-1, 3-glucan. Based on these findings, it was further discovered that recombinant TcGNBP1 can directly bind to five different bacteria in a Ca2+-dependent manner. After knockdown of TcGNBP1 with RNA interference, expression of antimicrobial peptide genes and prophenoloxidase (proPO) activity were suppressed, the susceptibility of T. castaneum to E. coli or S. aureus infection was enhanced, leading to low survival rate. These results suggest a regulatory mechanism of TcGNBP1 in innate immunity of T. castaneum and provide a potential molecular target for dsRNA-based insect pest management.

Inhibition of mevalonate pathway by macrophage-specific delivery of atorvastatin prevents their pro-inflammatory polarisation

Adjustment of the cellular metabolism of pro-inflammatory macrophages is essential for their bactericidal function; however, it underlies the development of many human diseases if induced chronically. Therefore, intervention of macrophage metabolic polarisation has been recognised as a potent strategy for their treatment. Although many small-molecule inhibitors affecting macrophage metabolism have been identified, their in vivo administration requires a tool for macrophage-specific delivery to limit their potential side effects. Here, we establish Drosophila melanogaster as a simple experimental model for in vivo testing of macrophage-specific delivery tools. We found that yeast-derived glucan particles (GPs) are suitable for macrophage-specific delivery of small-molecule inhibitors. Systemic administration of GPs loaded with atorvastatin, the inhibitor of hydroxy-methyl-glutaryl-CoA reductase (Hmgcr), leads to intervention of mevalonate pathway specifically in macrophages, without affecting HMGCR activity in other tissues. Using this tool, we demonstrate that mevalonate pathway is essential for macrophage pro-inflammatory polarisation and individual's survival of infection.

Developmental stage-specific proteome analysis of the legume pod borer Maruca vitrata provides insights on relevant proteins

The spotted pod borer, Maruca vitrata (Lepidoptera: Crambidae) is a destructive insect pest that inflicts significant productivity losses on important leguminous crops. Unravelling insect proteomes is vital to comprehend their fundamental molecular mechanisms. This research delved into the proteome profiles of four distinct stages -three larval and pupa of M. vitrata, utilizing LC-MS/MS label-free quantification-based methods. Employing comprehensive proteome analysis with fractionated datasets, we mapped 75 % of 3459 Drosophila protein orthologues out of which 2695 were identified across all developmental stages while, 137 and 94 were exclusive to larval and pupal stages respectively. Cluster analysis of 2248 protein orthologues derived from MaxQuant quantitative dataset depicted six clusters based on expression pattern similarity across stages. Consequently, gene ontology and protein-protein interaction network analyses using STRING database identified cluster 1 (58 proteins) and cluster 6 (25 proteins) associated with insect immune system and lipid metabolism. Furthermore, qRT-PCR-based expression analyses of ten selected proteins-coding genes authenticated the proteome data. Subsequently, functional validation of these chosen genes through gene silencing reduced their transcript abundance accompanied by a marked increase in mortality among dsRNA-injected larvae. Overall, this is a pioneering study to effectively develop a proteome atlas of M. vitrata as a potential resource for crop protection programs.

Ingestion of heat-killed pathogens confers transgenerational immunity to the pathogens via the vitellogenin-hypopharyngeal gland axis in honeybees

Honeybee diseases are a serious threat to beekeeping and pollination. Transgenerational immune priming (TGIP) has been attracting increasing attention as a promising strategy to protect honeybee colonies from infections. This study investigated whether feeding honeybees (Apis mellifera) with a heat-killed pathogen cocktail can provide them with transgenerational immunity to these pathogens. We found that vitellogenin (Vg) and defensin-1 were highly upregulated in nurse bees upon feeding them with a cocktail of heat-killed Ascosphaera apis and Paenibacillus larvae (A + P cocktail). Pathogen-pattern-recognition receptor genes in the Toll signaling pathway were upregulated in nurse bees upon ingestion of the A + P cocktail. In the nurse bees of the hives supplied with the A + P cocktail, Vg was upregulated in the fat body, and the defensin-1 expression and Vg uptake in the hypopharyngeal glands were induced. Consequently, the major proteins in royal jelly were upregulated. In addition, defensin-1 was upregulated in the queen larvae and young worker larvae in these hives. In correlation, the young worker larvae showed high pathogen resistance to P. larvae infection. Thus, our findings imply that introduction of a heat-killed pathogen cocktail into hives is an efficient strategy for conferring honeybees with social immunity through TGIP.

Mechanisms and roles of the first stage of nodule formation in lepidopteran insects

Nodule formation is a process of cellular immunity in insects and other arthropods with open circulatory systems. Based on histological observations, nodule formation occurs in 2 stages. The first stage occurs immediately after microbial inoculation and includes aggregate formation by granulocytes. The second stage occurs approximately 2-6 h later and involves the attachment of plasmatocytes to melanized aggregates produced during the first stage. The first stage response is thought to play a major role in the rapid capture of invading microorganisms. However, little is known regarding how granulocytes in the hemolymph form aggregates, or how the first stage of the immunological response protects against invading microorganisms. Since the late 1990s, our understanding of the molecules and immune pathways that contribute to nodule formation has improved. The first stage of nodule formation involves a hemocyte-induced response that is triggered by pathogen-associated molecular pattern (PAMP) recognition proteins in the hemolymph regulated by a serine proteinase cascade and cytokine (Spätzle) and Toll signaling pathways. Hemocyte agglutination proceeds through stepwise release of biogenic amine, 5-HT, and eicosanoids that act downstream of the Toll pathway. The first stage of nodule formation is closely linked to melanization and antimicrobial peptide (AMP) production, which is critical for insect humoral immunity. Nodule formation in response to artificial inoculation with millions of microorganisms has long been studied. It has recently been suggested that this system is the original natural immune system, and enables insects to respond to a single invading microorganism in the hemocoel.

Clip-SP1 cleavage activates downstream prophenoloxidase activating protease (PAP) in Plutella xylostella

Melanization is a component of the humoral immune defense of insects and is induced by serine protease-mediated phenoloxidase (PO) catalysis. Prophenoloxidase (PPO) in the midgut of Plutella xylostella is activated by the CLIP domain serine protease (clip-SP) in response to Bacillus thuringiensis (Bt) infection, but the detailed signaling cascade following this activation is unknown. Here, we report that activation of clip-SP enhances PO activity in the P. xylostella midgut by cleaving three downstream PPO-activating proteases (PAPs). First, the expression level of clip-SP1 was increased in the midgut after Bt8010 infection of P. xylostella. Then, purified recombinant clip-SP1 was able to activate three PAPs - PAPa, PAPb and PAP3 - which in turn enhanced their PO activity in the hemolymph. Furthermore, clip-SP1 showed a dominant effect on PO activity compared to the individual PAPs. Our results indicate that Bt infection induces the expression of clip-SP1, which is upstream of a signaling cascade, to efficiently activate PO catalysis and mediate melanization in the midgut of P. xylostella. And it provides a basis for studying the complex PPO regulatory system in the midgut during Bt infection.

Rift Valley Fever Virus Primes Immune Responses in Aedes aegypti Cells

The ongoing global emergence of arthropod-borne (arbo) viruses has accelerated research into the interactions of these viruses with the immune systems of their vectors. Only limited information exists on how bunyaviruses, such as Rift Valley fever virus (RVFV), are sensed by mosquito immunity or escape detection. RVFV is a zoonotic phlebovirus (Bunyavirales; Phenuiviridae) of veterinary and human public health and economic importance. We have shown that the infection of mosquitoes with RVFV triggers the activation of RNA interference pathways, which moderately restrict viral replication. Here, we aimed to better understand the interactions between RVFV and other vector immune signaling pathways that might influence RVFV replication and transmission. For this, we used the immunocompetent Aedes aegypti Aag2 cell line as a model. We found that bacteria-induced immune responses restricted RVFV replication. However, virus infection alone did not alter the gene expression levels of immune effectors. Instead, it resulted in the marked enhancement of immune responses to subsequent bacterial stimulation. The gene expression levels of several mosquito immune pattern recognition receptors were altered by RVFV infection, which may contribute to this immune priming. Our findings imply that there is a complex interplay between RVFV and mosquito immunity that could be targeted in disease prevention strategies.

Transcriptome Analysis Reveals That C17 Mycosubtilin Antagonizes Verticillium dahliae by Interfering with Multiple Functional Pathways of Fungi

Verticillium wilt is a kind of soil-borne plant fungal disease caused by Verticillium dahliae (Vd). Vd 991 is a strong pathogen causing cotton Verticillium wilt. Previously, we isolated a compound from the secondary metabolites of Bacillus subtilis J15 (BS J15), which showed a significant control effect on cotton Verticillium wilt and was identified as C17 mycosubtilin. However, the specific fungistatic mechanism by which C17 mycosubtilin antagonizes Vd 991 is not clear. Here, we first showed that C17 mycosubtilin inhibits the growth of Vd 991 and affects germination of spores at the minimum inhibitory concentration (MIC). Morphological observation showed that C17 mycosubtilin treatment caused shrinking, sinking, and even damage to spores; the hyphae became twisted and rough, the surface was sunken, and the contents were unevenly distributed, resulting in thinning and damage to the cell membrane and cell wall and swelling of mitochondria of fungi. Flow cytometry analysis with ANNEXINV-FITC/PI staining showed that C17 mycosubtilin induces necrosis of Vd 991 cells in a time-dependent manner. Differential transcription analysis showed that C17 mycosubtilin at a semi-inhibitory concentration (IC50) treated Vd 991 for 2 and 6 h and inhibited fungal growth mainly by destroying synthesis of the fungal cell membrane and cell wall, inhibiting its DNA replication and transcriptional translation process, blocking its cell cycle, destroying fungal energy and substance metabolism, and disrupting the redox process of fungi. These results directly showed the mechanism by which C17 mycosubtilin antagonizes Vd 991, providing clues for the mechanism of action of lipopeptides and useful information for development of more effective antimicrobials.

OfGNBP silencing enhances the toxicity of Serratia marcescens Bizio (SM1) to Odontotermes formosanus (Shiraki)

The immunity of insects plays a vital role in their survival. Our experiments found that lipopolysaccharide (LPS) and glucono-δ-lactone (GDL) could influence the virulence of Serratia marcescens Bizio (SM1) to Odontotermes formosanus (Shiraki) by affecting the immunity. Gram-negative binding proteins (GNBPs) are an important pattern recognition proteins that play a crucial role in the innate immune system. Therefore, two OfGNBPs were cloned in O. formosanus. The expression of OfGNBPs was significantly changed by LPS,SM1 and GDL, not prick. In addition, the immune-related gene expression, the phenoloxidase activity and antibacterial activity of donor termites and recipient termites were significantly induced by SM1. Furthermore, the knockdown of OfGNBP by RNA interference reduced not only individual immunity but also social immunity in O. formosanus, which increased the virulence of SM1 to O. formosanus. Importantly, dsOfGNBP alone also had good control effect on O. formosanus. In summary, we concluded that dsOfGNBPs are important termite immunosuppressants.

Why vary what's working? Phase variation and biofilm formation in Francisella tularensis

The notoriety of high-consequence human pathogens has increased in recent years and, rightfully, research efforts have focused on understanding host-pathogen interactions. Francisella tularensis has been detected in an impressively broad range of vertebrate hosts as well as numerous arthropod vectors and single-celled organisms. Two clinically important subspecies, F. tularensis subsp. tularensis (Type A) and F. tularensis subsp. holarctica (Type B), are responsible for the majority of tularemia cases in humans. The success of this bacterium in mammalian hosts can be at least partly attributed to a unique LPS molecule that allows the bacterium to avoid detection by the host immune system. Curiously, phase variation of the O-antigen incorporated into LPS has been documented in these subspecies of F. tularensis, and these variants often display some level of attenuation in infection models. While the role of phase variation in F. tularensis biology is unclear, it has been suggested that this phenomenon can aid in environmental survival and persistence. Biofilms have been established as the predominant lifestyle of many bacteria in the environment, though, it was previously thought that Type A and B isolates of F. tularensis typically form poor biofilms. Recent studies question this ideology as it was shown that alteration of the O-antigen allows robust biofilm formation in both Type A and B isolates. This review aims to explore the link between phase variation of the O-antigen, biofilm formation, and environmental persistence with an emphasis on clinically relevant subspecies and how understanding these poorly studied mechanisms could lead to new medical countermeasures to combat tularemia.

Pre-exposure to Candida albicans induce trans-generational immune priming and gene expression of Musca domestica

Insects have the phenomenon of immune priming by which they can have enhanced protection against reinfection with the same pathogen, and this immune protection can be passed on to their offspring, which is defined as “trans-generational immune priming (TGIP).” But whether housefly possesses TGIP is still unclear. Therefore, we used the housefly as the insect model and Candida albicans as the pathogen to explore whether the housefly is capable of eliciting TGIP, and RNA sequencing (RNA-seq) was performed to explore the molecular mechanism of TGIP of the housefly. We found that the housefly possesses TGIP, and adults pre-exposed to heat-killed C. albicans could confer protection to itself and its offspring upon reinfection with a lethal dose of C. albicans. RNA-seq results showed that 30 and 154 genes were differentially expressed after adults were primed with heat-killed C. albicans (CA-A) and after offspring larvae were challenged with a lethal dose of C. albicans (CA-CA-G), respectively. Among the differentially expressed genes (DEGs), there were 23 immune genes, including 6 pattern recognition receptors (PRRs), 7 immune effectors, and 10 immunoregulatory molecules. More importantly, multiple DEGs were involved in the Toll signaling pathway and phagosome signaling pathway, suggesting that the Toll signaling pathway and phagocytosis might play important roles in the process of TGIP of housefly to C. albicans. Our results expanded on previous studies and provided parameters for exploring the mechanism of TGIP.

Transcriptome Analysis Reveals Early Hemocyte Responses upon In Vivo Stimulation with LPS in the Stick Insect Bacillus rossius (Rossi, 1788)

Simple Summary

Non-model insect species such as B. rossius suffer from a profound gap of knowledge regarding the temporal progression of physiological responses following the challenge with bacterial pathogens or cell wall components thereof. The reason for this mostly lies in the lack of genomic/transcriptomic resources, which would provide an unparalleled in-depth capacity in the analysis of molecular, biochemical, and metabolic mechanisms. We present a high-quality transcriptome obtained from high-coverage sequencing of hemocytes harvested from adult stick insect specimens both pre- and post-LPS stimulation. Such a resource served as the basis for a stringent differential gene expression and functional enrichment analyses, the results of which were characterized and discussed in depth. Selected transcripts encoding for C-type lectins and ML-domain containing proteins were further investigated from a phylogenetic perspective. Overall, these findings shed light on the physiological responses driven by a short-term LPS stimulation in the European stick insect.

Abstract

Despite a growing number of non-model insect species is being investigated in recent years, a greater understanding of their physiology is prevented by the lack of genomic resources. This is the case of the common European stick insect Bacillus rossius (Rossi, 1788): in this species, some knowledge is available on hemocyte-related defenses, but little is known about the physiological changes occurring in response to natural or experimental challenges. Here, the transcriptional signatures of adult B. rossius hemocytes were investigated after a short-term (2 h) LPS stimulation in vivo: a total of 2191 differentially expressed genes, mostly involved in proteolysis and carbohydrate and lipid metabolic processes, were identified in the de novo assembled transcriptome and in-depth discussed. Overall, the significant modulation of immune signals—such as C-type lectins, ML domain-containing proteins, serpins, as well as Toll signaling-related molecules—provide novel information on the early progression of LPS-induced responses in B. rossius.

Silencing β-1,3-glucan binding protein enhances the susceptibility of Plutella xylostella to entomopathogenic fungus Isaria cicadae

BACKGROUND

The diamondback moth, Plutella xylostella is a notorious pest of brassicaceae crops globally and has developed serious resistance to insecticide. Insects primarily rely on their innate immunity to defense against various pathogens. In this study, we investigated the immunological functions of a β-1,3-glucan binding protein from P. xylostella (PxβGBP) and evaluated its potential for biocontrolling P. xylostella.

RESULTS

The open reading frame of PxβGBP is 1422 bp encoding 473 amino acids residues. PxβGBP contained a CBM39 domain, a PAC domain and a GH16 domain and shared evolutionary conservation with other lepidoptera βGRPs. PxβGBP was strongly expressed in the third instar larvae and fat body. PxβGBP transcript levels increased significantly after the challenge with microbes, including Isaria cicadae, Escherichia coli and Staphylococcus aureus. PxβGBP was identified in P. xylostella larvae challenged by I cicadae, but not in the naïve insects. Recombinant PxβGBP can directly bind fungal and bacterial cells, and also agglutinate the cells of I cicadae, S. aureus and E coli in a zinc-dependent manner. Knockdown of PxβGBP via RNA interference significantly down-regulated the expression of antimicrobial peptide gene gloverin, and enhanced the susceptibility of P. xylostella to I. cicadae infection, leading to high mortality.

CONCLUSION

These results indicated that PxβGBP plays an important role in the immune response of P. xylostella against I. cicadae infection, and could serve as a potential novel target for pest control. © 2022 Society of Chemical Industry.

Rhodnius prolixus Hemolymph Immuno-Physiology: Deciphering the Systemic Immune Response Triggered by Trypanosoma cruzi Establishment in the Vector Using Quantitative Proteomics

Understanding the development of Trypanosoma cruzi within the triatomine vector at the molecular level should provide novel targets for interrupting parasitic life cycle and affect vectorial competence. The aim of the current study is to provide new insights into triatomines immunology through the characterization of the hemolymph proteome of Rhodnius prolixus, a major Chagas disease vector, in order to gain an overview of its immune physiology. Surprisingly, proteomics investigation of the immunomodulation of T. cruzi-infected blood reveals that the parasite triggers an early systemic response in the hemolymph. The analysis of the expression profiles of hemolymph proteins from 6 h to 24 h allowed the identification of a broad range of immune proteins expressed already in the early hours post-blood-feeding regardless of the presence of the parasite, ready to mount a rapid response exemplified by the significant phenol oxidase activation. Nevertheless, we have also observed a remarkable induction of the immune response triggered by an rpPGRP-LC and the overexpression of defensins 6 h post-T. cruzi infection. Moreover, we have identified novel proteins with immune properties such as the putative c1q-like protein and the immunoglobulin I-set domain-containing protein, which have never been described in triatomines and could play a role in T. cruzi recognition. Twelve proteins with unknown function are modulated by the presence of T. cruzi in the hemolymph. Determining the function of these parasite-induced proteins represents an exciting challenge for increasing our knowledge about the diversity of the immune response from the universal one studied in holometabolous insects. This will provide us with clear answers for misunderstood mechanisms in host-parasite interaction, leading to the development of new generation strategies to control vector populations and pathogen transmission.

Transgenic insect-resistant Bt cotton expressing Cry1Ac/1Ab does not harm the insect predator Geocoris pallidipennis

The large-scale commercial cultivation of genetically modified (GM) cotton has brought significant economic and environmental benefits. However, GM crops must undergo strict environmental monitoring and long-term observation. An important natural enemy insect in cotton fields, Geocoris pallidipennis, can ingest the Bt protein expressed in GM cotton by feeding on herbivorous insects that feed on the cotton. However, the potential risk of GM cotton to G. pallidipennis is still unclear. We here evaluated the effects of Bt cotton expressing the Cry1Ac/1Ab protein on nymphs and adults G. pallidipennis. Cry1Ac protein was detected in the midgut of the cotton bollworm, Helicoverpa armigera, after it ingested Bt cotton, and in the midgut of G. pallidipennis nymphs and adults preying on Bt-fed H. armigera. However, the survival rate, growth, development, and fecundity of G. pallidipennis were not adversely affected. Furthermore, G. pallidipennis cadherins, and those genes related to detoxification, antioxidant activity, nutrient utilization, and immune function were not differentially expressed in response to Cry1Ac exposure. Finally, we showed that Cry1Ac could not bind to brush border membrane vesicles (BBMV) proteins in G. pallidipennis nymphs or adults. In summary, these results indicate that the potential negative effect of transgenic Cry1Ac/1Ab cotton on the insect redator G. pallidipennis is negligible.

Lentinan Impairs the Early Development of Zebrafish Embryos, Possibly by Disrupting Glucose and Lipid Metabolism

LNT is the major biologically active substance extracted from Lentinus edodes (L. edodes). Although functional and pharmacological studies have demonstrated that LNT has multiple benefits for animals and humans, the safety assessment is far from sufficient. To evaluate the potential safety risk, larval zebrafish were continuously exposed to varying concentrations of LNT for 120 h. The 96 h LC50 of LNT was determined to be 1228 μg/mL, and morphological defects including short body length, reduced eye and swim bladder sizes and yolk sac edema were observed. In addition, LNT exposure significantly reduced the blood flow velocity and locomotor activity of larval zebrafish. The biochemical parameters were also affected, showing reduced glucose, triglyceride and cholesterol levels in zebrafish larvae after being exposed to LNT. Correspondingly, the genes involved in glucose and lipid metabolism were disrupted. In conclusion, the present study demonstrates the adverse potential of high concentrations of LNT on the development of zebrafish larvae in the early life stage.

Full-length transcriptome sequencing of Heliocidaris crassispina using PacBio single-molecule real-time sequencing

The lack of high-throughput sequencing data makes the research progress of Heliocidaris crassispina slow. Therefore, we used PacBio single-molecule real-time sequencing to generate the first full-length transcriptome. Here, 31,181 isoforms were obtained, with an average length of 2383.20 and a N50 length of 2732 bp. Meanwhile, 764 alternative splicing (AS) events, 5098 long-noncoding RNAs (LncRNAs), 6978 simple sequence repeats (SSRs), and 950 hypothetical transcript factors (TFs) were identified. Moreover, five key innate immune pattern recognition receptors (PRRs), including toll-like receptor (TLR), NACHT domain and leucine-rich repeat (NLR), scavenger receptor cysteine-rich (SRCR), peptidoglycan recognition proteins (PGRP), and gram-negative binding proteins (GNBP), were searched in the transcriptome. In addition, 37 isoforms enriched in KEGG and GO immune systems were also detected. The study provid abundant data support for the current research on H. crassispina.

Immune properties of invertebrate phenoloxidases

Melanin production from different types of phenoloxidases (POs) confers immunity from a variety of pathogens ranging from viruses and microorganisms to parasites. The arthropod proPO expresses a variety of activities including cytokine, opsonin and microbiocidal activities independent of and even without melanin production. Proteolytic processing of proPO and its activating enzyme gives rise to several peptide fragments with a variety of separate activities in a process reminiscent of vertebrate complement system activation although proPO bears no sequence similarity to vertebrate complement factors. Pathogens influence proPO activation and thereby what types of immune effects that will be produced. An increasing number of specialised pathogens - from parasites to viruses - have been identified who can synthesise compounds specifically aimed at the proPO-system. In invertebrates outside the arthropods phylogenetically unrelated POs are participating in melanization reactions obviously aimed at intruders and/or aberrant tissues.

Fungal α-1,3-Glucan as a New Pathogen-Associated Molecular Pattern in the Insect Model Host Galleria mellonella

Recognition of pathogen-associated molecular patterns (PAMPs) by appropriate pattern recognition receptors (PRRs) is a key step in activating the host immune response. The role of a fungal PAMP is attributed to β-1,3-glucan. The role of α-1,3-glucan, another fungal cell wall polysaccharide, in modulating the host immune response is not clear. This work investigates the potential of α-1,3-glucan as a fungal PAMP by analyzing the humoral immune response of the greater wax moth Galleria mellonella to Aspergillus niger α-1,3-glucan. We demonstrated that 57-kDa and 61-kDa hemolymph proteins, identified as β-1,3-glucan recognition proteins, bound to A. niger α-1,3-glucan. Other hemolymph proteins, i.e., apolipophorin I, apolipophorin II, prophenoloxidase, phenoloxidase activating factor, arylphorin, and serine protease, were also identified among α-1,3-glucan-interacting proteins. In response to α-1,3-glucan, a 4.5-fold and 3-fold increase in the gene expression of antifungal peptides galiomicin and gallerimycin was demonstrated, respectively. The significant increase in the level of five defense peptides, including galiomicin, corresponded well with the highest antifungal activity in hemolymph. Our results indicate that A. niger α-1,3-glucan is recognized by the insect immune system, and immune response is triggered by this cell wall component. Thus, the role of a fungal PAMP for α-1,3-glucan can be postulated.

Two atypical gram-negative bacteria-binding proteins are involved in the antibacterial response in the pea aphid (Acyrthosiphon pisum)

The activation of immune pathways is triggered by the recognition of pathogens by pattern recognition receptors (PRRs). Gram-negative bacteria-binding proteins (GNBPs)/β-1,3-glucan recognition proteins (βGRPs) are a conserved family of PRRs in insects. Two GNBPs are predicted in the genome database of pea aphids; however, little is known about their functions in the aphid immune system. Here, we show that pea aphid GNBPs possess domain architectures and sequence features distinct from those of typical GNBPs/βGRPs and that their expression is induced by bacterial infection. Knockdown of their expression by dsRNA resulted in lower phenoloxidase activity, higher bacterial loads and higher mortality in aphids after infection. Our data suggest that these two atypical GNBPs are involved in the antibacterial response in the pea aphid, likely acting as PRRs in the prophenoloxidase pathway.

Proteomics of purified lamellocytes from Drosophila melanogaster HopTum-l identifies new membrane proteins and networks involved in their functions

In healthy Drosophila melanogaster larvae, plasmatocytes and crystal cells account for 95% and 5% of the hemocytes, respectively. A third type of hemocytes, lamellocytes, are rare, but their number increases after oviposition by parasitoid wasps. The lamellocytes form successive layers around the parasitoid egg, leading to its encapsulation and melanization, and finally the death of this intruder. However, the total number of lamellocytes per larva remains quite low even after parasitoid infestation, making direct biochemical studies difficult. Here, we used the Hop^Tum-l mutant strain that constitutively produces large numbers of lamellocytes to set up a purification method and analyzed their major proteins by 2D gel electrophoresis and their plasma membrane surface proteins by 1D SDS-PAGE after affinity purification. Mass spectrometry identified 430 proteins from 2D spots and 344 affinity-purified proteins from 1D bands, for a total of 639 unique proteins. Known lamellocyte markers such as PPO3 and the myospheroid integrin were among the components identified with specific chaperone proteins. Affinity purification detected other integrins, as well as a wide range of integrin-associated proteins involved in the formation and function of cell-cell junctions. Overall, the newly identified proteins indicate that these cells are highly adapted to the encapsulation process (recognition, motility, adhesion, signaling), but may also have several other physiological functions (such as secretion and internalization of vesicles) under different signaling pathways. These results provide the basis for further in vivo and in vitro studies of lamellocytes, including the development of new markers to identify coexisting populations and their respective origins and functions in Drosophila immunity.

Influences of dietary vitamin D3 on growth, antioxidant capacity, immunity and molting of Chinese mitten crab (Eriocheir sinensis) larvae

This study investigates the effects of vitamin D₃ (VD₃) on growth performance, antioxidant capacity, immunity and molting of larval Chinese mitten crab Eriocheir sinensis. A total of 6,000 larvae (7.52 ± 0.10 mg) were fed with six isonitrogenous and isolipidic experimental diets with different levels of dietary VD₃ (0, 3000, 6000, 9000, 12000 and 36000 IU/kg) respectively for 23 days. The highest survival and molting frequency were found in crabs fed 6000 IU/kg VD₃. Weight gain, specific growth rate, and carapace growth significantly increased in crabs fed 3000 and 6000 IU/kg VD₃ compared to the control. Broken-line analysis of molting frequency, weight gain and specific growth rate against dietary VD₃ levels indicates that the optimal VD₃ requirement for larval crabs is 4825-5918 IU/kg. The highest whole-body VD₃ content occurred in the 12000 IU/kg VD₃ group, and the 25-dihydroxy VD₃ content decreased with the increase of dietary VD₃. The malonaldehyde content was lower than the control. Moreover, the superoxide dismutase activity, glutathione peroxidase and total antioxidant capacity of crab fed 6000 IU/kg VD₃ were significantly higher than in control. Crabs fed 9000 IU/kg showed the highest survival after 120 h of salinity stress, and the relative mRNA expressions indicate vitamin D receptor (VDR) is the important regulatory element in molting and innate immunity. The molting-related gene expressions showed that the response of crab to salinity was self-protective. This study would contribute to a new understanding of the molecular basis underlying molting and innate immunity regulation by vitamin D₃ in E. sinensis.

Differentially Expressed Genes in Hepatopancreas of Acute Hepatopancreatic Necrosis Disease Tolerant and Susceptible Shrimp (Penaeus vannamei)

Acute hepatopancreatic necrosis disease (AHPND) is a lethal disease in marine shrimp that has caused large-scale mortalities in shrimp aquaculture in Asia and the Americas. The etiologic agent is a pathogenic Vibrio sp. carrying binary toxin genes, pirA and pirB in plasmid DNA. Developing AHPND tolerant shrimp lines is one of the prophylactic approaches to combat this disease. A selected genetic line of Penaeus vannamei was found to be tolerant to AHPND during screening for disease resistance. The mRNA expression of twelve immune and metabolic genes known to be involved in bacterial pathogenesis were measured by quantitative RT-PCR in two populations of shrimp, namely P1 that showed susceptibility to AHPND, and P2 that showed tolerance to AHPND. Among these genes, the mRNA expression of chymotrypsin A (ChyA) and serine protease (SP), genes that are involved in metabolism, and crustin-P (CRSTP) and prophenol oxidase activation system 2 (PPAE2), genes involved in bacterial pathogenesis in shrimp, showed differential expression between the two populations. The differential expression of these genes shed light on the mechanism of tolerance against AHPND and these genes can potentially serve as candidate markers for tolerance/susceptibility to AHPND in P. vannamei. This is the first report of a comparison of the mRNA expression profiles of AHPND tolerant and susceptible lines of P. vannamei.

Development of Fish Immunity and the Role of β-Glucan in Immune Responses

Administration of β-glucans through various routes, including immersion, dietary inclusion, or injection, have been found to stimulate various facets of immune responses, such as resistance to infections and resistance to environmental stress. β-Glucans used as an immunomodulatory food supplement have been found beneficial in eliciting immunity in commercial aquaculture. Despite extensive research involving more than 3000 published studies, knowledge of the receptors involved in recognition of β-glucans, their downstream signaling, and overall mechanisms of action is still lacking. The aim of this review is to summarize and discuss what is currently known about of the use of β-glucans in fish.

Sex and burrowing behavior and their implications with lytic activity in the sand-dwelling spider Allocosa senex

The immune response can be costly. Studies in several arthropod species have indicated a trade-off between immunity and other life-history traits, including reproduction. In sexually dimorphic species in which females and males largely differ in their life history strategies and related energetic demands, we can expect to find sex differences in immune functions. Sex differences in immunity are well documented in vertebrates; however, we largely lack data from invertebrate systems. Lytic activity, the immune system's ability to lysate bacteria and viruses, has been widely used as a proxy for the strength of the immune response in several invertebrates. With this in mind, we used the burrowing wolf spider Allocosa senex to test differences in lytic activity between females and males. We also studied whether digging behavior affects the immune responses in this species. While females of A. senex construct simple refuges where they stay during the day, males construct deep burrows, which they donate to females after copulation. In accordance with our hypothesis, females showed higher lytic activity compared with males, and those males who dug showed higher levels of lytic activity than those that did not dig. Furthermore, male body condition and lytic activity did not correlate with burrow length, a trait under female choice in this species. Our results show sexual dimorphism in lytic activity responses, which are likely related to differences in life-history strategies and energetic requirements of each sex in A. senex spiders.

20-Hydroxyecdysone regulates the prophenoloxidase cascade to immunize Metarhizium anisopliae in Locusta migratoria

BACKGROUND

PPO (prophenoloxidase) cascade plays an important role in resisting invasion of entomogenous fungus. The 20-hydroxyecdysone (20E) exerts potent effect on the innate immunity in many insects. However, whether 20E controls the PPO cascade system against fungi and the regulatory mechanism in insects remains unclear.

RESULTS

In this study, both the proteome and transcriptome of Locusta migratoria were determined followed by the induction of 20E. Pattern recognition receptor GNBP-2 (Gram-negative binding proteins) has been identified that responded to 20E at both messenger RNA (mRNA) and protein levels. The PPO gene expression in fat body and PO (phenoloxidase) activity in plasma was found significantly induced after 20E injection and during the high-20E developmental stage. However, when 20E signal was blocked by RNA interference (RNAi) of ecdysone receptor, the expression level of PPO and PO activity failed to be increased by 20E. Thus, 20E could not significantly induce the expression of PPO gene and PO activity after RNAi of GNBP-2. Furthermore, 20E treatment notably enhanced the resistance of L. migratoria against Metarhizium anisopliae. Followed by of GNBP-2 silencing, the mortality of nymphs was significantly increased under the stress of Metarhizium anisopliae, and 20E injection could not increase the resistance.

CONCLUSION

The 20E regulates the PPO system to resist fungal invasion via regulating GNBP-2 in worldwide pest L. migratoria. Our results provide insight into the mechanism of how 20E enhances the antimicrobial immunity, and will be beneficial for modification of entomogenous fungi targeting on hormones and the immune system. © 2020 Society of Chemical Industry.

Molecular Targets and Related Biologic Activities of Fucoidan: A Review

Fucoidan-a marine natural active polysaccharide derived from brown algae with a variety of medicinal activities and low toxicity-has been used as clinical drug for renal diseases for nearly 20 years. The pharmacological mechanism of fucoidan has been well-investigated, based on target molecules and downstream signaling pathways. This review summarizes some important molecular targets of fucoidan and its related biologic activities, including scavenger receptor (SR), Toll-like receptors (TLRs), C-type lectin (CLEC) and some newly found target molecules, which may be beneficial for further understanding the pharmacological mechanism of fucoidan and discovering its new functions, as well as developing related clinical or adjuvant drugs and functional preparations.

Pattern recognition receptors in Drosophila immune responses

Insects, which lack the adaptive immune system, have developed sophisticated innate immune system consisting of humoral and cellular immune responses to defend against invading microorganisms. Non-self recognition of microbes is the front line of the innate immune system. Repertoires of pattern recognition receptors (PRRs) recognize the conserved pathogen-associated molecular patterns (PAMPs) present in microbes, such as lipopolysaccharide (LPS), peptidoglycan (PGN), lipoteichoic acid (LTA) and β-1, 3-glucans, and induce innate immune responses. In this review, we summarize current knowledge of the structure, classification and roles of PRRs in innate immunity of the model organism Drosophila melanogaster, focusing mainly on the peptidoglycan recognition proteins (PGRPs), Gram-negative bacteria-binding proteins (GNBPs), scavenger receptors (SRs), thioester-containing proteins (TEPs), and lectins.

Identification of two LGBPs (isoform1 and isoform2) and their function in AMP expression and PO activation in male hepatopancreas

Two lipopolysaccharides (LPS) and β-1, 3-glucan binding protein (LGBP), designated as PcLGBP isoform1 and PcLGBP isoform2, respectively, were identified from Procambarus clarkii in this study. The full-length cDNA of PcLGBP isoform1 was 1308 bp containing an open reading frame (ORF) of 1113 bp encoding a protein of 370 amino acids. The full-length cDNA of PcLGBP isoform2 was 1440 bp containing an ORF of 1245 bp encoding a protein of 414 amino acids. Predicted PcLGBP isoform1 and PcLGBP isoform 2 proteins contained a signal peptide, a glycoside hydrolase domain, and a low-complexity region. The difference between the two LGBP isoforms was that PcLGBP isoform2 had 44 more amino acids behind the signal peptide than the PcLGBP isoform1. The PcLGBP isoform1 and PcLGBP isoform2 transcripts mainly expressed in the hepatopancreas in female and male crayfish. Moreover, the expression levels of the two genes in the hepatopancreas were higher in male than that in female crayfish. Upon being challenged with Vibrio parahaemolyticus or LPS, the expression levels of PcLGBP isoform1 and PcLGBP isoform2 in the hepatopancreas of female and male crayfish were most significantly up-regulated at different time points. The transcripts of anti-lipopolysaccharide factors (ALF5, ALF6, ALF8, and ALF9) and crustins (CRU1, CRU2, CRU3, and CRU4) were evidently down-regulated in the hepatopancreas of V. parahaemolyticus-challenged total PcLGBP (including PcLGBP isoform1 and PcLGBP isoform2)-silenced male crayfish. In addition, the phenoloxidase (PO) activity in the hepatopancreas of male crayfish was evidently higher than that of female crayfish. PcLGBP knock down could significantly decrease the PO activity in the hepatopancreas lysate (HLS) in male crayfish. The PO activity of male crayfish HLS was significantly increased when incubated with a mixture of recombinant LGBP protein and LPS or β-1, 3 glucan. We conclude that LGBP isoforms from P. clarkii function as a pattern recognition protein for recognizing and binding LPS and β-1, 3 glucan, and thus regulate the synthesis of antimicrobial peptides and activate the prophenoloxidase system.

Phloroglucinol Treatment Induces Transgenerational Epigenetic Inherited Resistance Against Vibrio Infections and Thermal Stress in a Brine Shrimp (Artemia franciscana) Model

Emerging, infectious diseases in shrimp like acute hepatopancreatic necrosis disease (AHPND) caused by Vibrio parahaemolyticus and mortality caused by other Vibrio species such as Vibrio harveyi are worldwide related to huge economic losses in industrial shrimp production. As a strategy to prevent disease outbreaks, a plant-based phenolic compound could be used as a biocontrol agent. Here, using the brine shrimp (Artemia franciscana) as a model system, we showed that phloroglucinol treatment of the parental animals at early life stages resulted in transgenerational inherited increased resistance in their progeny against biotic stress, i.e., bacteria (V. parahaemolyticus AHPND strain and V. harveyi) and abiotic stress, i.e., lethal heat shock. Increased resistance was recorded in three subsequent generations. Innate immune-related gene expression profiles and potential epigenetic mechanisms were studied to discover the underlying protective mechanisms. Our results showed that phloroglucinol treatment of the brine shrimp parents significantly (P < 0.05) enhanced the expression of a core set of innate immune genes (DSCAM, proPO, PXN, HSP90, HSP70, and LGBP) in subsequent generations. We also demonstrated that epigenetic mechanisms such as DNA methylation, m6A RNA methylation, and histone acetylation and methylation (active chromatin marker i.e., H3K4Me3, H3K4me1, H3K27me1, H3 hyperacetylation, H3K14ac and repression marker, i.e., H3K27me3, H4 hypoacetylation) might play a role in regulation of gene expression leading toward the observed transgenerational inheritance of the resistant brine shrimp progenies. To our knowledge, this is the first report on transgenerational inheritance of a compound-induced robust protected phenotype in brine shrimp, particularly protected against AHPND caused by V. parahaemolyticus and vibriosis caused by V. harveyi. Results showed that epigenetic reprogramming is likely to play a role in the underlying mechanism.

In vivo administration of LPS and β-glucan generates the expression of a serum lectin and its cellular receptor in Cherax quadricarinatus

In crustaceans, it has been suggested that specific protection against pathogens could be triggered by vaccines and biological response modifiers; although the specific mechanisms of this protection have not been clarified yet. In the crayfish Cherax quadricarinatus, a humoral lectin (CqL) binds its own granular hemocytes through a specific receptor (CqLR) and increases the production of reactive oxygen species (ROS). In the present study, we challenged in vivo crayfishes with immunostimulants, β-glucan (200 μg/kg) or LPS (20 μg/kg), and identified the participation of cellular and humoral mechanisms. The stimulants generated a complex modification in the total hemocytes count (THC), as well as in the proportion of hemocyte subsets. At 2 h after the challenge, the largest value in THC was observed in either challenged crayfishes. Furthermore, at the same time, hyaline hemocytes were the most abundant subset in the hemolymph; after 6 h, granular hemocytes (GH) were the most abundant hemocyte subset. It has been observed that a specific subset of GH possesses a CqLR that has been related to ROS production. After 2 and 6 h of the β-glucan challenge, a significant increase in CqLR expression was observed in the three circulating hemocyte subsets; also, an increased expression of CqL was detected in a granular hemocytes sub-population. After 2 and 6 h of stimulation, the specific activity of the serum lectin challenged with β-glucan was 250% and 160% higher than in the LPS-treated-group, respectively (P < 0.05). Hemocytes from challenged crayfishes were stimulated ex vivo with CqL, ROS production was 180% higher in hemocytes treated with β-glucan + CqL than in hemocytes treated with LPS + CqL (P < 0.05). The results evidence the effectivity of immune stimulators to activate specific crayfish defense mechanisms, the participation of CqL and its receptor (CqLR) could play an important role in the regulation of immune cellular functions, like ROS production, in Cherax quadricarinatus.

Interleukin-2 (IL-2) in flounder (Paralichthys olivaceus): Molecular cloning, characterization and bioactivity analysis

Interleukin-2 (IL-2) is mainly produced by CD4⁺ T helper lymphocytes, which is an important immunomodulatory cytokine that primarily promotes activation, proliferation and differentiation of T cells. In the present study, flounder (Paralichthys olivaceus) interleukin 2 homologue (poIL-2) was identified for the first time, and its expression patterns were characterized in healthy, virus- or bacteria-infected flounder. The full-length cDNA sequences of poIL-2 was 989 bp with an open reading frame of 423 bp coding a polypeptide of 140 amino acids (aa). The deduced aa sequences shared low similarities (<53%) with other known fish IL-2s. Multiple alignment of aa sequences revealed that poIL-2 own the classical IL-2 family signature of "C-X(3)-EL-X(2)-(T/V)-(V/M/L)-(K/T/R)-X-EC" and "DS-X-(F/L)Y(A/T/S)P". In healthy flounder, IL-2 mRNA was highly expressed in PBLs, spleen and hindgut, and moderately expressed in gill, trunk kidney and stomach. PHA, LPS and Con-A could effectively induce poIL-2 expression in primary cultured peripheral blood leukocytes in vitro. poIL-2 transcripts were significantly up-regulated in spleen, kidney, gill and hindgut post infections with Edwardsiella tarda and Hirame novirhabdovirus (HIRRV). The eukaryotic expression vector encoding poIL-2 (pcIL-2) was constructed and intramuscularly injected, which could be successfully expressed in flounders and induced significantly higher expressions of six immune related genes including poIL-2, β-defensin, CD4-1, CD8α, IFN-γ and TNF-α compared with the injection with control plasmid. Moreover, pretreatment with pcIL-2 could markedly increase the survival rate of flounder challenged with HIRRV. Our results demonstrated that poIL-2 plays an important role in the induction of immune responses and immune defense against bacterial and virus infection, which indicated its potential use as an immunopotentiator to prevent diseases in flounder.

Arginine supplementation improves growth, antioxidant capacity, immunity and disease resistance of juvenile Chinese mitten crab, Eriocheir sinensis

To investigate the effects of arginine (Arg) on the growth, antioxidant capacity, immunity and disease resistance of juvenile Chinese mitten crab, three diets containing Arg levels at 1.72% (control), 2.73% and 3.72% were formulated and fed to Chinese mitten crab (0.22 ± 0.03 g) for eight weeks. The weight gain, ecdysterone and growth hormone in the serum, relative expression of insulin-like growth factor 2 in the hepatopancreas significantly increased in crabs fed the 2.73% and 3.72% Arg diets. The protein and lipid contents significantly increased in crabs fed the 3.72% Arg diet. The feed conversion ratios in crabs fed the diets with Arg additions were lower than in the control. Arg supplementation also enhanced the antioxidative capacity by increasing the activities of superoxide dismutase, catalase and the relative expression of Kelch-like ECH-associated protein 1 gene in the hepatopancreas, which subsequently decreased malondialdehyde content in the hepatopancreas. Besides, Arg also decreased nitric oxide content in the serum and the activity of nitric oxide synthetase in the hepatopancreas. The relative mRNA levels of crustin, relish, lysozyme and cryptocyanin genes were significantly upregulated by Arg supplementation. The activities of acid phosphatase and alkaline phosphatase in the serum significantly increased in crabs fed the 3.72% Arg diet than those in the control. Similarly, the relative mRNA levels of crustin, cryptocyanin and proPO genes were significantly upregulated in crabs fed the 2.73% Arg diet after lipopolysaccharide challenge, and in crabs fed the 3.72% Arg diet after the Poly (I:C) challenge. The crabs fed the 2.73% and 3.72% Arg diets had higher survival rate after bacterial infection than those fed the control diet. This study indicates that the addition of Arg to the diet at 2.7-3.7% can improve the growth, survival, antioxidant capacity, immunity and disease resistance in juvenile Chinese mitten crab.

A peptidoglycan recognition protein involved in immune recognition and immune defenses in Ruditapes philippinarum

Peptidoglycan recognition proteins (PGRPs) are important pattern recognition receptors in the innate immune system of invertebrates. In the study, a short PGRP (designed as RpPGRP) was identified and characterized from the manila clam Ruditapes philippinarum. The open reading frame of RpPGRP encoded a polypeptide of 249-amino acids with a calculated molecular mass of 27.2 kDa and an isoelectric point of 6.62. Multiple alignments and phylogenetic analysis strongly suggested that RpPGRP was a new member of the PGRP superfamily. In non-stimulated clams, RpPGRP exhibited different tissue expression pattern, and highly expressed in hepatopancreas and hemocytes. Expression of RpPGRP transcripts was significantly up-regulated in hemocytes of clams post Vibrio anguillarum or Micrococcus luteus challenge. The recombinant RpPGRP (rRpPGRP) exhibited high affinity to PGN, LPS and zymosan in a concentration-dependent manner. With a broad spectrum of bacterial binding activities, rRpPGRP exhibited strong agglutination activity to Escherichia coli, Vibrio splendidus, V. anguillarum and M. luteus. Furthermore, rRpPGRP exhibited Zn²⁺-dependent amidase activity and catalyzed the degradation of insoluble PGN. Especially, rRpPGRP exhibited significant antibacterial activity against E. coli and M. luteus. Moreover, the biofilm formation of E. coli could be inhibited after rRpPGRP incubation in the presence of Zn²⁺. This inhibitory effect of rRpPGRP might attribute to its amide bactericidal activity. Taken together, rRpPGRP played important roles in PGRP-mediated immune defense mechanisms, especially by recognizing antigens and eliminating bacteria.

β-Glucan successfully stimulated the immune system in different jawed vertebrate species

Several reports have shown the positive effects of β-glucans on the immune. Howeverthese studies have a broad experimental design including β-glucans compounds. Consequently, a study using the same β-glucan molecule, administration route and experimental design is needed to compare the effects of β-glucan across vertebrate species. For this end, during 28 days we fed four different vertebrate species: mice, dogs, piglets and chicks, with two β-glucan molecules (BG01 and BG02). We measured the serum interleukin 2 as an indicator of innate immune response, the neutrophils and monocytes phagocytosis index as a cellular response and antibody formation as an adaptive response. The results clearly showed that the different β-glucan molecules exhibited biologically differently behaviors, but both molecules stimulate the immune system in a similar pattern in these four species. This finding suggests that vertebrates shared similar mechanisms/patterns in recognizing the β-glucans and confirms the benefits of β-glucans across different vertebrate species.

Molecular characterization of a pattern recognition protein LGBP highly expressed in the early stages of mud crab Scylla paramamosain

The early developmental stages of the mud crab Scylla paramamosain suffer from high mortality caused by pathogen infections; however, few immune associated factors are known. Lipopolysaccharide and β-1,3-glucan-binding protein (LGBP) functions as a typical pathogen recognition receptor and plays an important role in the innate immune system of invertebrates. In this study we characterized a LGBP gene (SpLGBP) which was highly expressed in the late embryonic, zoea I larval stage and hepatopancreas of S. paramamosain.. It encodes 364 amino acids, composed of several conserved domains like the bacterial glucanase motif. The recombinant SpLGBP protein (rSpLGBP) was obtained through the E.coli expression system, in which two 6◊His-tags were added to both C and N terminals during vector construction for the improvement of purification efficiency. In vivo the study showed that the SpLGBP mRNA was significantly up-regulated under Vibrio parahaemolyticus and a lipopolysaccharide (LPS) challenge in the hemocytes and hepatopancreas. The ELISA binding assay in vitro indicated that the rSpLGBP was capable of binding to LPSs and peptidoglycan (PGN). The rSpLGBP could agglutinate both G+ and G- bacteria in the presence of Ca²⁺. Our results suggest that SpLGBP may play an immunological role against pathogenic infection in the early developmental stages of S. paramamosain.

Identification of a crustacean β-1,3-glucanase related protein as a pattern recognition protein in antibacterial response

Prophenoloxidase (proPO) activating system is an important immune response for arthropods. β-1, 3-glucanase related protein (previously named as lipopolysaccharide and β-1, 3-glucan binding protein (LGBP) in crustaceans) is a typical pattern recognition receptor family involved in the proPO activation by recognizing the invading microbes. In this study, we pay special attention to a bacteria-induced β-1,3-glucanase related protein from red swamp crayfish Procambarus clarkii, an important aquaculture specie in China. This protein, designated PcBGRP, was found a typical member of crustacean BGRP family with the glucanase-related domain and the characteristic motifs. PcBGRP was expressed in hemcoyes and hepatopancreas, and its expression could be induced by the carbohydrate and bacteria stimulants. The induction by lipopolysaccharide (LPS) and β-1,3-glucan (βG) was more significant than by peptidoglycan (PG). The response of PcBGRP to the native Gram-negative bacterial pathogen Aeromonas hydrophila was more obvious than to Gram-positive bacteria. Using RNA interference and recombinant protein, PcBGRP was found to protect crayfish from A. hydrophila infection revealed by the survival test and morphological analysis. A mechanism study found PcBGRP could bind LPS and βG in a dose-dependent manner, and the LPS recognizing ability determined the Gram-negative bacterium binding activity of PcBGRP. PcBGRP was found to enhance the PO activation both in vitro and in vivo, and the protective role was related to the PO activating ability of PcBGRP. This study emphasized the role of BGRP family in crustacean immune response, and provided new insight to the immunity of red swamp crayfish which suffered serious disease during the aquaculture in China.

Immune functions of insect βGRPs and their potential application

Insects rely completely on the innate immune system to sense the foreign bodies and to mount the immune responses. Germ-line encoded pattern recognition receptors play crucial roles in recognizing pathogen-associated molecular patterns. Among them, β-1,3-glucan recognition proteins (βGRPs) and gram-negative bacteria-binding proteins (GNBPs) belong to the same pattern recognition receptor family, which can recognize β-1,3-glucans. Typical insect βGRPs are comprised of a tandem carbohydrate-binding module in the N-terminal and a glucanase-like domain in the C-terminal. The former can recognize triple-helical β-1,3-glucans, whereas the latter, which normally lacks the enzymatic activity, can recruit adapter proteins to initiate the protease cascade. According to studies, insect βGRPs possess at least three types of functions. Firstly, some βGRPs cooperate with peptidoglycan recognition proteins to recognize the lysine-type peptidoglycans upstream of the Toll pathway. Secondly, some directly recognize fungal β-1,3-glucans to activate the Toll pathway and melanization. Thirdly, some form the 'attack complexes' with other immune effectors to promote the antifungal defenses. The current review will focus on the discovery of insect βGRPs, functions of some well-characterized members, structure-function studies and their potential application.

Immune responses to bacterial and fungal infections in the silkworm, Bombyx mori

The silkworm Bombyx mori, an economically important insect that is usually reared indoors, is susceptible to various pathogens, including bacteria, fungi, viruses, and microsporidia. As with other insects, the silkworm lacks an adaptive immune system and relies solely on innate immunity to defend itself against infection. Compared to other intensively studied insects, such as the fruit fly and tobacco hornworm, the principal immune pathways in the silkworm remain unclear. In this article, we review the literature concerning silkworm immune responses to bacteria and fungi and present our perspectives on future research into silkworm immunity.

Laminarin Promotes Immune Responses and Reduces Lactate Dehydrogenase But Increases Glutamic Pyruvic Transaminase in Normal Mice In Vivo

BACKGROUND/AIM

Laminarin, a typical component of fungal cell walls, has been shown to induce immune responses in both adult and larval locusts. We investigated the effects of laminarin on immune response and glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT) and lactate dehydrogenase (LDH) levels in normal mice.

MATERIALS AND METHODS

Thirty-six normal BALB/c mice were randomly divided into four groups and treatments were provided by gavage. Group I mice acted as normal control; mice of groups II-IV received laminarin at different doses (100 μl at 1, 2.5 and 5.0 mg/mouse in double-distilled water, respectively). All animals were treated for 14 days and were weighed, blood was collected for determination of cell markers, liver and spleen samples were weighed. Spleens were used for phagocytosis and determination of natural killer (NK) cell activity and cell proliferation by flow cytometric assay.

RESULTS

Laminarin reduced the body weights and weights of liver and spleen. Laminarin increased CD3, CD19 and Mac-3 cell populations at 2.5 and 5 mg/mouse, however, these did not affect CD11b marker levels. Laminarin (1 and 5 mg/mouse) reduced macrophage phagocytosis from peripheral blood mononuclear cells, but did not affect phagocytosis by macrophages from the peritoneal cavity. At an effector:target ratio of 50:1, laminarin reduced NK cell cytotoxic activity at all levels, but at a ratio of 25:1, only at 1 mg treatment. Laminarin did not affect T-cell and B-cell proliferation. Laminarin increased the level of GPT and reduced that of LDH at all doses, indicating laminarin can protect against liver injury. Laminarin is worthy of investigation in future experiments on improving immune responses.

Lipopolysaccharide- and β-1,3-glucan-binding protein from Litopenaeus vannamei: Purification, cloning and contribution in shrimp defense immunity via phenoloxidase activation

Lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) existed in diversity of invertebrates including shrimp plays a crucial role in an innate immunity via mediating the recognition of invading pathogens. In this study, LGBP was cloned and characterized from the hepatopancreas of Litopenaeus vannamei, named as LvLGBP. Its full-length cDNA of 1282 bp contained an open reading frame (1101 bp) encoding a peptide of 367 amino acids. The LGBP primary structure contained a glycosyl hydrolase domain, two integrin binding motifs, two kinase C phosphorylation sites, and two polysaccharide recognition motifs which were identified as a polysaccharide binding motif and a β-1,3-glucan recognition motif. The LvLGBP transcripts were expressed mainly in the hepatopancreas. Upon challenge with Vibrio parahaemolyticus or white spot syndrome virus (WSSV), the LvLGBP mRNA expression was significantly up-regulated to reach a maximum at 48 h post injection. Its expression was also induced by lipopolysaccharide (LPS) or β-1,3-glucan stimulation. RNAi-based silencing resulted in the critical suppression of LvLGBP expression. Knockdown of LvLGBP gene with co-inoculation by V. parahaemolyticus or WSSV led to increase in the cumulative mortality and reduce in the median lethal time. Native LGBP was detected only in the hepatopancreas as verified by Western blotting. Purified LGBP from the hepatopancreas exhibited the agglutinating and binding activity towards Gram-negative bacterium V. parahaemolyticus with calcium-dependence. Its agglutinating activity was dominantly inhibited by LPS with higher potential than β-1,3-glucan. Purified LvLGBP could significantly activate the hemocyte phenoloxidase activity in the presence of LPS (12.9 folds), while slight activation was detected with β-1,3-glucan (2.0 folds). It could enhance the encapsulation by hemocytes but did not have antibacterial activity. These results provided evidence that LvLGBP might act as a pathogenic recognition protein to activate shrimp immune defense against invading pathogens via the agglutination, binding and enhancing encapsulation and phenoloxidase activity of the hemocytes.