Identification and comparative analysis of three novel C-type lectins from the silkworm with functional implications in pathogen recognition

Hemocytin, the special aggregation factor connecting insect hemolymph immunity, a potential target of insecticidal immunosuppresant

Insects possess an effective innate immunity that enables them to adapt to their intricate living environment and fend off various pathogens (or parasites). This innate immunity comprises both humoral and cellular immunity, which synergistically orchestrate immune responses. Hemocytin, a lectin with a distinctive structure, plays a crucial role in insect hemolymph immunity. Hemocytin is involved in the early immune response, facilitating processes such as coagulation, nodulation, and encapsulation in the hemolymph. It prevents hemolymph overflow and microbial pathogens invasion resulting from epidermal damage, and also aids in the recognition and elimination of invaders. However, the research on hemocytin is still limited. Our previous findings demonstrated that destruxin A effectively inhibits insect hemolymph immunity by interacting with hemocytin, suggesting that hemocytin could be a potential target for insecticides development. Therefore, it is crucial to gain a deeper understanding of hemocytin. This review integrates recent advancements in the study of the structure and function of insect hemocytin and also explores the potential of hemocytin as a target for insecticides. This review aims to enhance our comprehension of insect innate immunity and provide innovative ideas for the development of environmentally friendly pesticides.

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.

Functional Analysis of a CTL-X-Type Lectin CTL16 in Development and Innate Immunity of Tribolium castaneum

C-type lectins (CTLs) are a class of proteins containing carbohydrate recognition domains (CRDs), which are characteristic modules that recognize various glycoconjugates and function primarily in immunity. CTLs have been reported to affect growth and development and positively regulate innate immunity in Tribolium castaneum. However, the regulatory mechanisms of TcCTL16 proteins are still unclear. Here, spatiotemporal analyses displayed that TcCTL16 was highly expressed in late pupae and early adults. TcCTL16 RNA interference in early larvae shortened their body length and narrowed their body width, leading to the death of 98% of the larvae in the pupal stage. Further analysis found that the expression level of muscle-regulation-related genes, including cut, vestigial, erect wing, apterous, and spalt major, and muscle-composition-related genes, including Myosin heavy chain and Myosin light chain, were obviously down-regulated after TcCTL16 silencing in T. castaneum. In addition, the transcription of TcCTL16 was mainly distributed in the hemolymph. TcCTL16 was significantly upregulated after challenges with lipopolysaccharides, peptidoglycans, Escherichia coli, and Staphylococcus aureus. Recombinant CRDs of TcCTL16 bind directly to the tested bacteria (except Bacillus subtilis); they also induce extensive bacterial agglutination in the presence of Ca²⁺. On the contrary, after TcCTL16 silencing in the late larval stage, T. castaneum were able to develop normally. Moreover, the transcript levels of seven antimicrobial peptide genes (attacin2, defensins1, defensins2, coleoptericin1, coleoptericin2, cecropins2, and cecropins3) and one transcription factor gene (relish) were significantly increased under E. coli challenge and led to an increased survival rate of T. castaneum when infected with S. aureus or E. coli, suggesting that TcCTL16 deficiency could be compensated for by increasing AMP expression via the IMD pathways in T. castaneum. In conclusion, this study found that TcCTL16 could be involved in developmental regulation in early larvae and compensate for the loss of CTL function by regulating the expression of AMPs in late larvae, thus laying a solid foundation for further studies on T. castaneum CTLs.

Immune functions of pattern recognition receptors in Lepidoptera

Pattern recognition receptors (PRRs), as the "sensors" in the immune response, play a prominent role in recognizing pathogen-associated molecular patterns (PAMPs) and initiating an effective defense response to pathogens in Lepidoptera. It is becoming increasingly clear that damage-associated molecular patterns (DAMPs) normally play a physiological role within cells; however, when exposed to extracellular, they may become "part-time" critical signals of the immune response. Based on research in recent years, we review herein typical PRRs of Lepidoptera, including peptidoglycan recognition protein (PGRP), gram-negative binding protein (GNBP), β-1,3-glucan recognition protein (βGRP), C-type lectin (CTL), and scavenger receptor (SR). We also outline the ways in which DAMPs participate in the immune response and the correlation between PRRs and immune escape. Taken together, these findings suggest that the role of PRRs in insect innate immunity may be much greater than expected and that it is possible to recognize a broader range of signaling molecules.

RNAi-mediated silencing of an egg-specific gene Nllet1 results in hatch failure in the brown planthopper

BACKGROUND

The brown planthopper (BPH) is one of the most destructive agricultural pests in Asia. RNA interference (RNAi)-mediated pest management has been under development for years, and the selection of appropriate target genes is important for pest-targeted RNAi. C-type lectins (CTLs) are a class of genes that perform a variety of functions, such as the regulation of growth and development.

RESULTS

A CTL-S protein named Nllet1, containing a single calcium ion (Ca²⁺ )-dependent carbohydrate-binding domain (CRD) with a conserved triplet motif QPD was identified and functionally characterized in BPH. Expression profiles at both the transcriptional and translational levels show that Nllet1 accumulates during the serosal cuticle (SC) formation period. Immunofluorescence and immunogold labeling further demonstrated that Nllet1 is located in the serosal endocuticle (en-SC). Maternal RNAi-mediated silencing of Nllet1 disrupted the SC structure, accompanied by a loss of the outward barrier and 100% embryo mortality. Injection of 10 ng dsNllet1 or dsNllet1' per female adult BPH resulted in a total failure of egg hatching.

CONCLUSION

Nllet1 is essential for SC formation and embryonic development in BPH, which helps us understand the important roles of CTL-Ss. Additionally, BPH eggs show high sensitivity to the depletion of Nllet1. This study indicates that Nllet1 is a promising candidate gene that can be used to develop RNAi-based control strategies at the BPH egg stage, and it can also be used as a target for developing novel ovicides. © 2022 Society of Chemical Industry.

Functional analysis of TcCTL12 in innate immunity and development in Tribolium castaneum

C-type lectins (CTLs) play vital roles in invertebrates' innate immunity. Six CTL-X type lectins are identified in Tribolium castaneum. However, their functions and regulating mechanisms remain elusive. Here, TcCTL12, one CTL-X, was identified and cloned from T. castaneum. Spatiotemporal expression profiling revealed that TcCTL12 highly expressed in late pupa and early adult of T. castaneum in comparison with other developmental stages, and exhibited the highest expression level in the haemolymph and central nervous system (CNS). Then, the expression of TcCTL12 was remarkably induced by the stimulation of Escherichia coli and Staphylococcus aureus. Moreover, the recombinant protein TcCTL12 could bind pathogen-associated molecular patterns (PAMPs) including LPS and PGN, and displayed agglutinative activity to both Gram-positive and Gram-negative bacteria in a calcium-dependent manner in vitro. Furthermore, RNAi of TcCTL12 caused T. castaneum pupation and eclosion defected. The abnormal pupa thinned their epidermal, and appeared the abnormal development of muscle cell compared with the control group. Additionally, depletion of TcCTL12 resulted in reducing fertility of offspring and affected their fecundity. In sum, these results indicated that TcCTL12 had extensive functions in the regulation of development in T. castaneum, in addition to the immune response. It further expanded insights into CTL functions in insects.

Functions of a C-type lectin with a single carbohydrate-recognition domain in the innate immunity and movement of the red flour beetle, Tribolium castaneum

C-type lectins (CTLs) are a superfamily of proteins found in almost all vertebrates and invertebrates. They play an important role in innate immune defences, development and epidermal structure. Here, a CTL with one carbohydrate-recognition domain containing a highly conserved Gln-Pro-Asp (QPD) motif was identified in Tribolium castaneum and given the name TcCTL5. Spatiotemporal analyses showed that Tcctl5 was highly expressed in the late pupa stage and mainly existed in the central nervous system and haemolymph. The transcript level of Tcctl5 was prominently induced after bacterial infection. Recombinant TcCTL5 proteins (rTcCTL5) were found to bind to lipopolysaccharide, peptidoglycan and tested bacteria and induce microbial agglutination in the presence of Ca²⁺ . Interestingly, when Tcctl5 was knocked down, the transcript level of antimicrobial peptides (AMPs) (attacin1, defensins3, coleoptericin1 and cecropins3) was prominently downregulated after induction with Gram-negative Escherichia coli. More interestingly, Tcctl5 was knocked down, leading to increased mortality and loss of locomotor activity, which exhibited less travel distances among early adults. These results demonstrate that Tcctl5 plays an important role in the innate immune reaction and the movement of T. castaneum. Thus, it may represent an alternative molecular target for pest control and thus reduce the use of pesticides in agricultural production.

A Pattern Recognition Receptor C-type Lectin-S6 (CTL-S6) is Involved in the Immune Response in the Silkworm (Lepidoptera: Bombycidae)

Insect innate immunity is initiated by the special recognition and binding of the foreign pathogens, which is accomplished by the pattern recognition receptors (PRRs). As an important type of PRRs, C-type lectins (CTLs) play various roles in insect innate immunity, including pathogen recognition, stimulation of prophenoloxidase, regulation of cellular immunity and so on. In this study, we have cloned the full-length cDNA of a CTL gene named CTL-S6 from the silkworm, Bombyx mori. The open reading frame (ORF) of B. mori CTL-S6 encodes 378 amino acids, which contain a secretion signal peptide. The mRNA of CTL-S6 exhibited the highest transcriptional level in the midgut. Its transcriptional level increased dramatically in fat body and hemocytes upon Escherichia coli or Micrococcus luteus challenge. Purified recombinant CTL-S6 could bind to bacterial cell wall components, including peptidoglycan (PGN, from Bacillus subtilis) and lipopolysaccharide (LPS, from E. coli 0111:B4), and recombinant CTL-S6 was involved in the encapsulation and melanization of hemocytes. Furthermore, the addition of recombinant CTL-S6 to the hemolymph of silkworm resulted in a significant increase in phenoloxidase activity. Overall, our results indicated that B. mori CTL-S6 may serve as a PRR for the recognition of foreign pathogens, prophenoloxidase pathway stimulation and involvement in the innate immunity.

A C-type lectin with dual-CRD from Tribolium castaneum is induced in response to bacterial challenge

BACKGROUND

C-type lectins (CTLs), a group of pattern recognition receptors, are involved in regulating the immune response of insects and could be used as potential targets for pest control. However, information about roles of CTLs in the innate immunity of Tribolium castaneum, a serious, worldwide pest that damages stored grain products, is relatively scarce.

RESULTS

Here, a CTL with dual carbohydrate recognition domains (CRDs) containing a highly conserved WHD (Trp⁵³ -His⁵⁴ -Asp⁵⁵ ) motif was identified in T. castaneum and named as TcCTL3. Spatiotemporal analysis showed that TcCTL3 was highly expressed in all developmental stages except early eggs, and mainly distributed in central nervous system and hemolymph. The transcript levels of TcCTL3 were significantly increased after lipopolysaccharide (LPS) and peptidoglycan (PGN) stimulation. Recombinant TcCTL3 was able to bind directly to LPS, PGN and all tested bacteria and induce a broad spectrum of microbial agglutination in the presence of Ca²⁺ . The binding was shown mainly through CRD1 domain of TcCTL3. When TcCTL3 was knocked down by RNA interference, expression of nine antimicrobial peptides (AMPs) (attacin1, attacin2, attacin3, defensins1, defensins2, coleoptericin1, coleoptericin2, cecropins2 and cecropins3) and four transcription factors (TFs) (dif1, dif2, relish and jnk) were significantly decreased under LPS and PGN stimulation, leading to increased mortality of T. castaneum when infected with Gram-positive Staphylococcus aureus or Gram-negative Escherichia coli infection.

CONCLUSION

TcCTL3 could mediate the immune response in T. castaneum via the pattern recognition, agglutination and AMP expression. These findings indicate a potential mechanism of TcCTL3 in resisting bacteria and provide an alternative molecular target for pest control. © 2020 Society of Chemical Industry.

C-type lectin 5, a novel pattern recognition receptor for the JAK/STAT signaling pathway in Bombyx mori

The Janus kinase/signal transducer and activator of transcription cascade transduction (JAK/STAT) signaling pathway is highly conserved in mammals, but the pattern recognition receptors (PRRs) and their functions are unclear. We found that the expression pattern of Bombyx mori C-type lectin 5 (BmCTL 5) had a synergy relevance with the JAK/STAT signaling pathway against Beauveria bassiana. An RNAi assay, subcellular localization analysis, yeast two-hybrid technique, protein recruitment experiment and pathogen infection tests were used to explore the roles of BmCTL 5 in the JAK/STAT signaling pathway. Knock-down of the BmCTL 5 suppressed the JAK/STAT signaling pathway and the PO cascade of nodule melanization. BmCTL 5 is located in the cytomembrane and interacted with BmHOP both in yeast and B. mori ovary cells N (BmN cells). BmCTL 5 and the JAK/STAT signaling pathway was activated by B. bassiana but only slightly activated by B. mori cytoplasmic polyhedrosis virus (BmCPV), Nosema bombycis and bacteria LPS. These findings suggest that BmCTL 5 might be an important PRR for the JAK/STAT signaling pathway and may mediate the nodule melanization for fungi infection. These data provide insights into the immune mechanism of the JAK/STAT signaling pathway in insects and aid understanding of the mechanism of the JAK/STAT signaling pathway and adaptive immune systems in mammals.

A C-type lectin with a single carbohydrate-recognition domain involved in the innate immune response of Tribolium castaneum

C-type lectins are one of the pattern-recognition proteins involved in innate immunity in invertebrates. Although there are 16 C-type lectin genes that have been identified in the genome of Tribolium castaneum, their functions and mechanisms in innate immunity remain unknown. Here, we identified one C-type lectin orthologue, TcCTL6 (TC003708), by sequencing random clones from the cDNA library of the coleopteran beetle, T. castaneum. TcCTL6 contains a 654 bp open reading frame encoding a protein of 217 amino acids that includes a single carbohydrate-recognition domain. The expression of TcCTL6 was significantly induced by Escherichia coli, Staphylococcus aureus and stimulation with carbohydrates, including lipopolysaccharide and peptidoglycan. A binding assay suggested that the recombinant TcCTL6 not only bound to lipopolysaccharide and peptidoglycan but also bound to Gram-positive (S. aureus, Bacillus subtilis and Bacillus thuringiensis) and Gram-negative bacteria (E. coli and Pseudomonas aeruginosa) in the presence of calcium ions. Furthermore, when TcCTL6 was knocked down by RNA interference, four antimicrobial peptides (attacin1, attacin2, coleoptericin1 and coleoptericin2) were significantly decreased. These results demonstrate that TcCTL6 plays a vital role in the immune response towards pathogen infection by influencing the expression of antimicrobial peptides and the agglutination of bacteria in the presence of calcium ions in T. castaneum.

Comparative analysis of C-type lectin domain proteins in the ghost moth, Thitarodes xiaojinensis (Lepidoptera: Hepialidae)

Insects have a large family of C-type lectins involved in cell adhesion, pathogen recognition and activation of immune responses. In this study, 32 transcripts encoding C-type lectin domain proteins (CTLDPs) were identified from the Thitarodes xiaojinensis transcriptome. According to their domain structures, six CTLDPs with one carbohydrate-recognition domain (CRD) were classified into the CTL-S subfamily. The other 23 CTLDPs with two CRDs were grouped into the immulectin (IML) subfamily. The remaining three with extra regulatory domains were sorted into the CTL-X subfamily. Phylogenetic analysis showed that CTL-S and CTL-X members from different insects could form orthologous groups. In contrast, no T. xiaojinensis IML orthologues were found in other insects. Remarkable lineage-specific expansion in this subfamily was observed reflecting that these CTLDPs, as important receptors, have evolved diversified members in response to a variety of microbes. Prediction of binding ligands revealed that T. xiaojinensis, a cold-adapted species, conserved the ability of CRDs to combine with Ca²⁺ to keep its receptors from freezing. Comparative analysis of induction of CTLDP genes after different immune challenges indicated that IMLs might play critical roles in immune defenses. This study examined T. xiaojinensis CTLDPs and provides a basis for further studies of their characteristics.

Insect C-type lectins in innate immunity

C-type lectins (CTLs) are a family of proteins that contain characteristic modules of carbohydrate-recognition domains (CRDs) and they possess the binding activity to ligands in a calcium-dependent manner. CTLs play important roles in animal immune responses, and in insects, they are involved in opsonization, nodule formation, agglutination, encapsulation, melanization, and prophenoloxidase activation, as well as in maintaining gut microbiome homeostasis. In this review, we will summarize insect CTLs, compare the properties of insect CTLs with vertebrate CTLs, and focus mainly on the domain organization and functions of insect CTLs in innate immunity.

Identification and Characterization of C-type Lectins in Ostrinia furnacalis (Lepidoptera: Pyralidae)

C-type lectins (CTLs) are a large family of calcium-dependent carbohydrate-binding proteins. They function primarily in cell adhesion and immunity by recognizing various glycoconjugates. We identified 14 transcripts encoding proteins with one or two CTL domains from the transcriptome from Asian corn borer, Ostrinia furnacalis (Guenée; Lepidoptera: Pyralidae). Among them, five (OfCTL-S1 through S5) only contain one CTL domain, the remaining nine (OfIML-1 through 9) have two tandem CTL domains. Five CTL-Ss and six OfIMLs have a signal peptide are likely extracellular while another two OfIMLs might be cytoplasmic. Phylogenetic analysis indicated that OfCTL-Ss had 1:1 orthologs in Lepidoptera, Diptera, Coleoptera and Hymenoptera species, but OfIMLs only clustered with immulectins (IMLs) from Lepidopteran. Structural modeling revealed that the 22 CTL domains adopt a similar double-loop fold consisting of β-sheets and α-helices. The key residues for calcium-dependent or independent binding of specific carbohydrates by CTL domains were predicted with homology modeling. Expression profiles assay showed distinct expression pattern of 14 CTLs: the expression and induction were related to the developmental stages and infected microorganisms. Overall, our work including the gene identification, sequence alignment, phylogenetic analysis, structural modeling, and expression profile assay would provide a valuable basis for the further functional studies of O. furnacalis CTLs.

Characterization of two groups of Spodoptera exigua Hübner (Lepidoptera: Noctuidae) C-type lectins and insights into their role in defense against the densovirus JcDV

Insect innate immunity relies on numerous soluble and membrane-bound receptors, named pattern recognition proteins (PRPs), which enable the insect to recognize pathogen-associated molecular patterns. C-type lectins are among the best-studied PRPs and constitute the most diverse family of animal lectins. Here we have characterized two groups of Spodoptera exigua C-type lectins that differ in their phylogeny, domain architecture, and expression pattern. One group includes C-type lectins with similar characteristics to other lepidopteran lectins, and a second group includes bracoviral-related lectins (bracovirus-like lectins, Se-BLLs) recently acquired by horizontal gene transfer. Subsequently, we have investigated the potential role of some selected lectins in the susceptibility to Junonia coenia densovirus (JcDV). For this purpose, three of the bracoviral-related lectins were expressed, purified, and their effect on the densovirus infection to two different Spodoptera species was assessed. The results showed that Se-BLL3 specifically reduce the mortality of Spodoptera frugiperda larvae caused by JcDV. In contrast, no such effect was observed with S. exigua larvae. In a previous work, we have also shown that Se-BLL2 increased the tolerance of S. exigua larvae to baculovirus infection. Taken together, these results confirm the implication of two different C-type lectins in antiviral response and reflect the biological relevance of the acquisition of bracoviral genes in Spodoptera spp.

Gene expression and molecular characterization of a novel C-type lectin, encapsulation promoting lectin (EPL), in the rice armyworm, Mythimna separata

Insect cellular immune reactions differ depending on the target species. Phagocytosis is activated to scavenge microorganisms such as bacteria and fungi. On the other hand, larger invaders such as parasitoid wasps are eliminated by activation of encapsulation. In this study, we hypothesized that novel determinants regulate cellular immunities independent of surface molecular pattern recognition involving pattern recognition receptors (PRRs). Immune-related genes differentially expressed depending on the treated material size were screened in larval hemocytes of the rice armyworm, Mythimna separata. Consequently, we identified a novel C-type lectin gene up-regulated by injection of large beads but not small beads of identical material. Examination of in vitro effect of the recombinant protein on the immune reactions clarified that the protein activated encapsulation reaction, while it suppressed phagocytosis. These results suggest that this novel C-type lectin designated "encapsulation promoting lectin (EPL)" regulates cellular immunity by a novel immune target size-recognition mechanism.

Molecular cloning and analysis of a C-type lectin from silkworm Bombyx mori

C-type lectins (CTLs) play a variety of roles in plants and animals. They are involved in animal development, pathogen recognition, and the activation of immune responses. CTLs carry one or more non-catalytic carbohydrate-recognition domains (CRDs) to bind specific carbohydrates reversibly. Here, we report the molecular cloning and functional analysis of a single-CRD CTL, named C-type lectin-S2 (BmCTL-S2) from the domesticated silkmoth Bombyx mori (Lepidoptera: Bombycidae). The ORF of CTL-S2 is 666 bp, which encodes a putative protein of 221 amino acids. BmCTL-S2 is expressed in a variety of immune-related tissues, including hemocytes and fat body among others. BmCTL-S2 mRNA level in the midgut and the fat body was significantly increased by bacterial challenges. The recombinant protein (rBmCTL-S2) bound different bacterial cell wall components and bacterial cells. rBmCTL-S2 also inhibited the growth of Bacillus subtilis and Staphylococcus aureus. Taken together, we infer that BmCTL-S2 is a pattern-recognition receptor with antibacterial activities.

Differential responses of Helicoverpa armigera C-type immunlectin genes to the endoparasitoid Campoletis chlorideae

The C-type lectins mediate nonself recognition in insects. The previous studies focused on host immunlectin response to bacterial infection; however, the molecular basis of immunlectin reactions to endoparasitoids has not been elucidated. The present study investigated the effect of parasitization by Campoletis chlorideae on hemagglutination activity (HA; defined as the ability of lectin to agglutinate erythrocytes or other cells), and transcriptional expression of C-type immunlectin genes in the larval host, Helicoverpa armigera. Parasitization induced four- to eightfold higher HA in the parasitized larvae, compared to nonparasitized larvae at days 2 and 6 postparasitization (PP), however inhibited HA at other days PP. Eight C-type lectins were differentially expressed in different host developmental stages, from feeding to wandering stage. The mRNA levels of HaCTL1, HaCTL3, HaCTL4, and HaCTL5 were upregulated and HaCTL2 and HaCTL7 were downregulated. Tissue analysis showed that HaCTLs were mainly expressed in fat body or hemocytes, while HaCTL5 was highly expressed in testes. The effects of parasitization on the lectin expression patterns differed. Lectins except HaCTL6 or HaCTL5 were significantly down- or upregulated in parasitized larvae at day 4 or 6 PP compared with that of nonparasitized larvae. We infer from our results that C-type immunlectins are involved in host-parasitoid interactions, and parasitization alter host immunlectin levels both in inhibiting and promoting host immune defenses to endoparasitoids. These immunlectin genes indicated an altered physiological status of the host insect, depending on developmental stage, tissue, and parasitization.

Identification of the Mamestra configurata (Lepidoptera: Noctuidae) peritrophic matrix proteins and enzymes involved in peritrophic matrix chitin metabolism

The peritrophic matrix (PM) is essential for insect digestive system physiology as it protects the midgut epithelium from damage by food particles, pathogens, and toxins. The PM is also an attractive target for development of new pest control strategies due to its per os accessibility. To understand how the PM performs these functions, the molecular architecture of the PM was examined using genomic and proteomic approaches in Mamestra configurata (Lepidoptera: Noctuidae), a major pest of cruciferous oilseed crops in North America. Liquid chromatography-tandem mass spectrometry analyses of the PM identified 82 proteins classified as: (i) peritrophins, including a new class with a CBDIII domain; (ii) enzymes involved in chitin modification (chitin deacetylases), digestion (serine proteases, aminopeptidases, carboxypeptidases, lipases and α-amylase) or other reactions (β-1,3-glucanase, alkaline phosphatase, dsRNase, astacin, pantetheinase); (iii) a heterogenous group consisting of polycalin, REPATs, serpin, C-Type lectin and Lsti99/Lsti201 and 3 novel proteins without known orthologs. The genes encoding PM proteins were expressed predominantly in the midgut. cDNAs encoding chitin synthase-2 (McCHS-2), chitinase (McCHI), and β-N-acetylglucosaminidase (McNAG) enzymes, involved in PM chitin metabolism, were also identified. McCHS-2 expression was specific to the midgut indicating that it is responsible for chitin synthesis in the PM, the only chitinous material in the midgut. In contrast, the genes encoding the chitinolytic enzymes were expressed in multiple tissues. McCHS-2, McCHI, and McNAG were expressed in the midgut of feeding larvae, and NAG activity was present in the PM. This information was used to generate an updated model of the lepidopteran PM architecture.

A novel C-type lectin with triple carbohydrate recognition domains has critical roles for the hard tick Haemaphysalis longicornis against Gram-negative bacteria

C-type lectins (CLecs) play an important role in innate immunity against invaders. In this study, a novel CLec was identified from Haemaphysalis longicornis ticks (HlCLec). HlCLec contains a signal peptide and a transmembrane region. Interestingly, HlCLec possesses three dissimilar carbohydrate recognition domains (CRDs). Each CRD contains the mutated motif of Ca(2+)-binding site 2. HlCLec mRNA was up-regulated during blood feeding, and had highest expression in the midgut and ovary. HlCLec localization was also confirmed by immunofluorescent antibody test (IFAT). HlCLec was found on the cell membrane and basal lamina of midgut and ovary. In addition, the recombinant HlCLec and individual CRDs demonstrated direct binding activity to Escherichia coli and Staphylococcus aureus; however, no growth inhibition activity was observed. Furthermore, E. coli injection after silencing of HlCLec caused drastic reduction in survival rate of ticks. These results strongly suggest the key role of HlCLec in tick innate immunity against Gram-negative bacteria.

Identification of C-type lectin-domain proteins (CTLDPs) in silkworm Bombyx mori

C-type lectins (CTLs) represent a large family of proteins that can bind carbohydrate moieties normally in a calcium-dependent manner. CTLs play important roles in mediating cell adhesion and the recognition of pathogens in the immune system. In the present study, we have identified 23 CTL genes in domestic silkworm Bombyx mori. CTL-domain proteins (CTLDPs) are classified into three groups based on the number of carbohydrate-recognition domains (CRDs) and the domain architectures. These include twelve CTL-S (Single-CRD), six immulectins (Dual-CRD) and five CTL-X (CRD with other domains). We studied their phylogenetic features, analyzed the conserved residues, predicted tertiary structures, and examined the tissue expression profile and immune inducibility. Through bioinformatics analysis, we have putatively identified ten secretory and two cytoplasmic CTL-S; four secretory and two cytoplasmic immulectins; one secretory, one cytoplasmic and three transmembrane forms of CTL-X. Most B. mori CTLDPs form monophyletic groups with orthologs from Lepidoptera, Diptera, Coleoptera and Hymenoptera species. Immulectins of B. mori and Manduca sexta evolved from common ancestor genes perhaps due to gene duplication events of CTL-S ancestor genes. Homology modeling revealed that the overall structures of B. mori CTL domains are analogous to those of humans with a variable loop region. We examined the expression profile of CTLDP genes in naïve and immune-stimulated tissues. The expression and induction of CTLDP genes were related to the tissues and microorganisms. Together, our gene identification, sequence comparison, phylogenetic analysis, homology modeling and expression analysis laid a good foundation for the further studies of B. mori CTLDPs and comparative genomics.

Involvement of a pattern recognition receptor C-type lectin 7 in enhancing cellular encapsulation and melanization due to its carboxyl-terminal CRD domain in the cotton bollworm, Helicoverpa armigera

C-type lectins play important roles in innate immunity as pattern recognition receptors (PRRs). We have previously reported a novel C-type lectin HaCTL7 from the cotton bollworm (Helicoverpa armigera) which contains two carbohydrate-recognition domains (CRDs), namely N-terminal CRD1 and C-terminal CRD2. Interestingly, there are four but not six of conserved cysteine residues in CRD2 of HaCTL7, which is different from that of other dual CRD C-type lectins. In the current study, we expressed and purified recombinant HaCTL7 (rHaCTL7) as well as rCRD1 and rCRD2, and demonstrated that both rHaCTL7 and rCRD2, but not rCRD1, owned the agglutinate ability against both Gram-negative and Gram-positive bacteria in a calcium dependent manner. In addition, both rHaCTL7 and rCRD2, but not rCRD1, could bind to various bacteria, and enhanced haemocytes mediated encapsulation and melanization processes. HaCTL7 secreted from fat bodies is able to bind to granulocytes, plasmatocytes and oenocytoids, but not to spherulocytes. Recombinant HaCTL7 and rCRD2 are capable of binding to both granulocytes and oenocytoids, while rCRD1 can only bind to granulocytes. Our data suggest that as a PRR HaCTL7 enhances encapsulation and melanization likely through its C-terminal CRD2, but not N-terminal CRD1, which imply that the characteristic four cysteine structure of CRD2 plays key roles in innate immunity.

Comparative proteomic analysis of Bombyx mori hemocytes treated with destruxin A

Destruxin A (DA), a cyclodepsipeptidic secondary metabolite of the entomopathogenic fungus, Metarhizium anisopliae, is an important anti-immunity agent against insect hemocytes. To understand the mechanism of the molecular responses to DA, fifth-instar larvae of the silkworm, Bombyx mori, were injected with 2 μg of DA. The proteomics of hemocytes were then investigated using two-dimensional electrophoresis and mass spectrometry, and validated qPCR. As a result, a total of 47 differently expressed protein spots were detected and 22 proteins in 26 spots were identified. There are eight immunity-related proteins, including three downregulated proteins (antitrypsin isoform 3, p50 protein, and calreticulin precursor) and five upregulated proteins (C-type lectin 10 precursor, serine proteinase-like protein, paralytic peptide, PPO-1, and PPO-2). Four resistance- and/or stress-related proteins (arginine kinase, carboxylesterase clade H, member 1, aminoacylase, and thiol peroxiredoxin) were upregulated. Ten proteins with other or unknown functions were also recorded. Five selected proteins were verified with qPCR. These results provide new insights into the molecular mechanism of host immune response to DA challenge.

A novel pattern recognition protein of the Chinese oak silkmoth, Antheraea pernyi, is involved in the pro-PO activating system

In this paper, we firstly reported a C-type lectin cDNA clone of 1029 bps from the larvae of A. Pernyi (Ap-CTL) using PCR and RACE techniques. The full-length cDNA contains an open reading frame encoding 308 amino acid residues which has two different carbohydrate-recognition domains (CRDs) arranged in tandem. To investigate the biological activities in the innate immunity, recombinant Ap-CTL was expressed in E. coli with a 6-histidine at the amino-terminus (Ap-rCTL). Besides acted as a broad-spectrum recognition protein binding to a wide range of PAMPs and microorganisms, Ap-rCTL also had the ability to recognize and trigger the agglutination of bacteria and fungi. In the proPO activation assay, Ap-rCTL specifically restored the PO activity of hemolymph blocked by anti- Ap-rCTL antibody in the presence of different PAMPs or microorganisms. In summary, Ap-rCTL plays an important role in insect innate immunity as an pattern recognition protein.

Genome-wide transcriptional response of silkworm (Bombyx mori) to infection by the microsporidian Nosema bombycis

Microsporidia have attracted much attention because they infect a variety of species ranging from protists to mammals, including immunocompromised patients with AIDS or cancer. Aside from the study on Nosema ceranae, few works have focused on elucidating the mechanism in host response to microsporidia infection. Nosema bombycis is a pathogen of silkworm pébrine that causes great economic losses to the silkworm industry. Detailed understanding of the host (Bombyx mori) response to infection by N. bombycis is helpful for prevention of this disease. A genome-wide survey of the gene expression profile at 2, 4, 6 and 8 days post-infection by N. bombycis was performed and results showed that 64, 244, 1,328, 1,887 genes were induced, respectively. Up to 124 genes, which are involved in basal metabolism pathways, were modulated. Notably, B. mori genes that play a role in juvenile hormone synthesis and metabolism pathways were induced, suggesting that the host may accumulate JH as a response to infection. Interestingly, N. bombycis can inhibit the silkworm serine protease cascade melanization pathway in hemolymph, which may be due to the secretion of serpins in the microsporidia. N. bombycis also induced up-regulation of several cellular immune factors, in which CTL11 has been suggested to be involved in both spore recognition and immune signal transduction. Microarray and real-time PCR analysis indicated the activation of silkworm Toll and JAK/STAT pathways. The notable up-regulation of antimicrobial peptides, including gloverins, lebocins and moricins, strongly indicated that antimicrobial peptide defense mechanisms were triggered to resist the invasive microsporidia. An analysis of N. bombycis-specific response factors suggested their important roles in anti-microsporidia defense. Overall, this study primarily provides insight into the potential molecular mechanisms for the host-parasite interaction between B. mori and N. bombycis and may provide a foundation for further work on host-parasite interaction between insects and microsporidia.

Phenoloxidase activity acts as a mosquito innate immune response against infection with Semliki Forest virus

Several components of the mosquito immune system including the RNA interference (RNAi), JAK/STAT, Toll and IMD pathways have previously been implicated in controlling arbovirus infections. In contrast, the role of the phenoloxidase (PO) cascade in mosquito antiviral immunity is unknown. Here we show that conditioned medium from the Aedes albopictus-derived U4.4 cell line contains a functional PO cascade, which is activated by the bacterium Escherichia coli and the arbovirus Semliki Forest virus (SFV) (Togaviridae; Alphavirus). Production of recombinant SFV expressing the PO cascade inhibitor Egf1.0 blocked PO activity in U4.4 cell- conditioned medium, which resulted in enhanced spread of SFV. Infection of adult female Aedes aegypti by feeding mosquitoes a bloodmeal containing Egf1.0-expressing SFV increased virus replication and mosquito mortality. Collectively, these results suggest the PO cascade of mosquitoes plays an important role in immune defence against arboviruses.

Arboviruses are transmitted to vertebrates by arthropod vectors such as mosquitoes. Infection of mosquitoes with arboviruses activates immune defence responses including the RNA interference pathway. Another component of the insect immune system is the phenoloxidase (PO) cascade, which produces melanin that accumulates at wound sites and around invading microorganisms. Some pathogen-associated pattern recognition molecules are known to activate the PO cascade, which results in the proteolytic processing of inactive prophenoloxidase (PPO) to PO. PO then catalyses the formation of compounds that ultimately form melanin. Some of these products are also known to have anti-microbial properties but whether activation of the PO cascade provides any defence against arboviruses is unclear. Using the arbovirus, Semliki Forest virus, we show that this virus activates the PO cascade. By using recombinant Semliki Forest virus expressing an inhibitor of the PO cascade, we also demonstrate that this pathway inhibits virus spread in cell culture. Moreover, inhibition of this pathway leads to higher virus genome levels and higher mortality of infected mosquitoes. In conclusion, Semliki Forest virus activates the PO cascade which exhibits antiviral activity and can be added to the list of mosquito anti-viral defence mechanisms.

cDNA Cloning and Expression Analysis of Pattern Recognition Proteins from the Chinese Oak Silkmoth, Antheraea pernyi

Pattern recognition receptors play an important role in insect immune defense. We cloned the β-1,3-glucan recognition protein, lectin-5 and C-type lectin 1 genes of Antheraea pernyi and examined the expression profiles of immune-stimulated pupae. After infection with Bacillus subtilis, Escherichia coli, Antheraea pernyi nuclear polyhedrosis virus (ApNPV) and Saccharomyces cerevisiae, respectively, the pupae showed different gene expression levels in the different tissues examined (midgut, fatbody, epidermis, testis, and hemocytes). ApβGRP and Aplectin-5 was induced by all the microorganisms, and mainly in epidermis and hemocytes, but not in testis; Aplectin-5 was also expressed in fatbody. Ap C-type lectin 1 was, on the contrary, highly expressed in testis and also in fatbody, but not in hemocytes. Unlike ApβGRP and Aplectin-5, Ap C-type lectin 1 was not induced by Gram-positive bacteria. The results suggest that the cloned lectins may have different functions in different tissues of A. pernyi.

Immune response of four dual-CRD C-type lectins to microbial challenges in giant freshwater prawn Macrobrachium rosenbergii

C-type lectins (CTLs) are believed to play important roles in the innate immunity of invertebrates and serve as pattern recognition receptors, opsonins, or effector molecules. In this study, the full-lengths cDNA of 4 CTL genes from giant freshwater prawn Macrobrachium rosenbergii were cloned and designated as MrLec1, MrLec2, MrLec3, and MrLec4. All of these 4 lectin cDNAs encode proteins with 2 carbohydrate recognition domains (CRDs). While MrLec1, MrLec3, and MrLec4 had signal peptides, no signal peptide was detected in MrLec2. Two carbohydrate recognition motifs within two CRDs of each lectin were predicted (QPE, EPG in MrLec1; EPT, EPA in MrLec2; QPT, NPR in MrLec3; KPN, EPD in MrLec4). Phylogenetic analysis showed that MrLec4 belongs to group A whereas MrLec1, MrLec2, and MrLec3 belong to group B. Positive selection in dual-CRD lectins suggested their probable roles in innate immunity, and positively selected induced amino acid diversity of lectins may confer their ability to recognize a broad range of microbes. The qRT-PCR analysis in adult prawns showed that MrLec1 is mainly expressed in the hepatopancreas, gills, and stomach, MrLec2 and MrLec4 are mainly distributed in the hepatopancreas, and MrLec3 is mainly expressed in the hepatopancreas and stomach. Time-course analysis using qRT-PCR showed that MrLec1 to MrLec4 are all upregulated by the Vibrio anguillarum challenge. MrLec1 is upregulated after 2, 12, and 24 h of white spot syndrome virus (WSSV) challenge. The expression of MrLec2 increases after 12 and 24 h of WSSV challenge, and the transcript of MrLec3 and MrLec4 are downregulated after 2 h of WSSV challenge. The results suggest the potential roles of dual-CRD lectins in the innate immunity of M. rosenbergii.

Expression profiles of six novel C-type lectins in response to bacterial and 20E injection in the cotton bollworm (Helicoverpa armigera)

C-type lectins can act as pattern recognition receptors (PRRs) and play an important role in innate immunity. Two C-type lectins (HaCTL1 and HaCTL2) have been previously identified in the cotton bollworm (Helicoverpa armigera). Here we isolate six C-type lectins from H. armigera (HaCTL3, 4, 5, 6, 7 and 8). All six new HaCTLs encode a signal peptide (or partial signal peptide) and complete tandem carbohydrate-recognition domains (CRDs). HaCTL4, 5, 6, 7 and 8 mRNA increased in the fat body after injection with both killed Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, whereas HaCTL3 mRNA was upregulated following E. coli injection only. Recombinant HaCTL3 exhibited agglutinating activity against both Gram-negative and Gram-positive bacteria in a calcium-dependent manner. Agglutination inhibitory analysis indicated that rHaCTL3 recognizes maltose, trehalose, peptidoglycan and lipopolysaccharides. HaCTL3 and HaCTL8 mRNA showed upregulation while HaCTL4, 5, and 6 mRNA downregulation post 20-Hydroxyecdysone (20E) injection. Our results indicate that the six novel C-type lectins of H. armigera may play important roles in defending against bacteria as PRRs and the hormone 20E can function in regulating immunity through lectins.

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

Background

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

Methodology/Principal Findings

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

Conclusions/Significance

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

The extended loop of the C-terminal carbohydrate-recognition domain of Manduca sexta immulectin-2 is important for ligand binding and functions

Our previous research showed that immulectin-2 (IML-2), a C-type lectin from the tobacco hornworn, Manduca sexta, is a pattern recognition receptor (PRR) that can bind to pathogen-associated molecular patterns (PAMPs), such as lipopolysaccharide (LPS), peptidoglycan (PG) and β-1,3-glucan, and IML-2 plays an important role in cellular encapsulation, melanization, phagocytosis, and prophenoloxidase (proPO) activation. Unlike most mammalian C-type lectins that contain a single carbohydrate-recognition domain (CRD), IML-2 is composed of tandem CRDs, and the C-terminal CRD2 contains an extended loop, which is not present in most C-type CRDs. We hypothesize that the extended loop may participate in ligand binding, encapsulation, melanization, phagocytosis and/or proPO activation in M. sexta. To test this hypothesis, two deletion mutant proteins (IML-2Δ220-244 and IML-2Δ220-257), in which the extended loop of the CRD2 was partially or completely deleted, were expressed and purified. By comparing the characteristics of recombinant IML-2, IML-2Δ220-244 and IML-2Δ220-257, we found that deletion of the extended loop in CRD2 impaired the ability of IML-2 to bind microbial PAMPs and to stimulate proPO activation, indicating that the extended loop of IML-2 plays an important role in ligand binding and biological functions.

Immunity in lepidopteran insects

Lepidopteran insects provide important model systems for innate immunity of insects, particularly for cell biology of hemocytes and biochemical analyses of plasma proteins. Caterpillars are also among the most serious agricultural pests, and understanding of their immune systems has potential practical significance. An early response to infection in lepidopteran larvae is the activation of hemocyte adhesion, leading to phagocytosis, nodule formation, or encapsulation. Plasmatocytes and granular cells are the hemocyte types involved in these responses. Infectious microorganisms are recognized by binding of hemolymph plasma proteins to microbial surface components. This "pattern recognition" triggers phagocytosis and nodule formation, activation of prophenoloxidase and melanization and the synthesis of antimicrobial proteins that are secreted into the hemolymph. Many hemolymph proteins that function in such innate immune responses of insects were first discovered in lepidopterans. Microbial proteinases and nucleic acids released from lysed host cells may also activate lepidopteran immune responses. Hemolymph antimicrobial peptides and proteins can reach high concentrations and may have activity against a broad spectrum of microorganisms, contributing significantly to clearing of infections. Serine proteinase cascade pathways triggered by microbial components interacting with pattern recognition proteins stimulate activation of the cytokine Spätzle, which initiates the Toll pathway for expression of antimicrobial peptides. A proteinase cascade also results inproteolytic activation of phenoloxidase and production of melanin coatings that trap and kill parasites and pathogens. The proteinases in hemolymph are regulated by specific inhibitors, including members of the serpin superfamily. New developments in lepidopteran functional genomics should lead to much more complete understanding of the immune systems of this insect group.

Localization of the serine protease homolog BmSPH-1 in nodules of E. coli-injected Bombyx mori larvae and functional analysis of its role in nodule melanization

The molecular mechanisms underlying nodule formation and melanization, an important pathogen defense mechanism in insects, are poorly understood. In this study, we investigated the role of BmSPH-1, a catalytically inactive Bombyx mori serine protease homolog, in nodule melanization induced by injection of Escherichia coli cells into the B. mori larval hemocoel. Addition of the melanization substrate L-3,4-dihydroxyphenylalanine (DOPA) to newly formed nodules prompted nodule melanization, confirming that nodules contain activated prophenoloxidase needed for melanization. Immunoprecipitation and immunoblot studies demonstrated that BmSPH-1 interacts with BmLBP, a C-type lectin that binds Gram-negative bacteria, and that BmSPH-1 is present in a truncated, putatively activated form at the E. coli cell surface in nodules. Pretreatment of larvae with anti-BmSPH-1 serum inhibited nodule melanization in E. coli-injected larvae. These results suggest that BmSPH-1 regulates nodule melanization and is recruited into nodules from the hemolymph by BmLBP.

Cloning and molecular modeling of Litopenaeus vannamei (Penaeidae) C-type lectin homologs with mutated mannose binding domain-2

C-type lectins are animal proteins that contain at least one carbohydrate recognition domain (CRD) capable of mediating sugar and calcium binding. Carbohydrate recognition is directly required for some biological functions, including the innate immune response. We cloned two novel C-type lectin (CTL) precursors from the commercial marine shrimp Litopenaeus vannamei. The cloned cDNAs encompass ORFs of 1044 nucleotides and encode highly similar two-domain polypeptides of 347 residues. The predicted proteins, LvCTL-br1 and -br2, contain the consensus triad that recognizes galactose (-GlnProAsp-) in CRD1 but also contain a mutated mannose-binding site (-GluProAsn-) in the second domain (CRD2). Phylogenetic analysis of LvCTL-br1 and -br2 and hundreds of CTL-like domain-containing proteins have allowed grouping of penaeid shrimp CTLs into three functional clusters. Reverse transcription coupled to PCR indicated that LvCTL-br1 expression is induced in shrimp gills upon IHHNV infection. Computational molecular modeling of LvCTL-br1 and -br2 revealed that three amino acid substitutions in CRD1 occur near the sugar binding site. Also, the 3-D models show a long loop of LvCTL-br1 CRD2 that might accommodate complex sugars. The structural data, evolutionary history and functional analysis support the hypothesis that gene duplication and accelerated evolution have caused functional diversification of penaeid shrimp C-type lectins.

Characterization of two C-type lectin-like domain (CTLD)-containing proteins from the cDNA library of Chinese mitten crab Eriocheir sinensis

Chinese mitten crab Eriocheir sinensis is one of the most important aquaculture crustacean species in China. A cDNA library was constructed from mixed tissues of E. sinensis challenged with LPS. Eight genes involved in immune response were identified from 319 single colonies. Among them, two different C-type lectin-like domain (CTLD)-containing proteins were firstly identified in Chinese mitten crab. The full-length cDNA sequences of two C-type lectin-like domain (CTLD)-containing proteins named EsCTLDcp-1 and EsCTLDcp-2 were cloned by 5' RACE. The deduced amino acid sequences of EsCTLDcp-1 and EsCTLDcp-2 possessed several conserved features of C-type lectin subfamily. The tissue distribution of EsCTLDcp-1 and EsCTLDcp-2 was examined by Real-time PCR. In the normal Chinese mitten crab, the expression of EsCTLDcp-2 was detected in all tested tissues such as haemolymph, muscle, intestine, gill, heart, gonad and hepatopancreas, whereas in muscle, intestine, gill, heart and hepatopancreas for EsCTLDcp-1. The highest expressions of EsCTLDcp-1 and EsCTLDcp-2 were both observed in hepatopancreas. LPS significantly induced the expression of EsCTLDcp-1 and EsCTLDcp-2 in the hepatopancreas at the different time points. The induced fold change of EsCTLDcp-1 and EsCTLDcp-2 increased significantly from 2 h for EsCTLDcp-1 and 4 h for EsCTLDcp-2, and reached a maximum at 12 h, then dropped at 24 h. A differential pattern was found in Chinese mitten crab challenged with Chinese mitten crab pathogen Aeromonas hydrophila. The expression of EsCTLDcp-1 increased significantly at 2 h post-challenge crabs with A. hydrophila, then decreased at 4 h and 8 h, after that increased at 12 h and 24 h. The expression of EsCTLDcp-2 was decreased at the all time points. All these data suggest a differential role of EsCTLDcp-1 and EsCTLDcp-2 in the crab innate immune response to bacterial infection.

Changes in the proteomes of the hemocytes and fat bodies of the flesh fly Sarcophaga bullata larvae after infection by Escherichia coli

Background

Insects have an efficient self-defense system that is based on innate immunity. Recent findings have disclosed many parallels between human and insect innate immunity, and simultaneously fine differences in the processes between various species have been revealed. Studies on the immune systems of various insect species may uncover the differences in their host defense strategies.

Results

We analyzed the proteomes of the hemocytes and fat bodies of Sarcophaga bullata larvae after infection by Escherichia coli. The 2-DE gels of the hemocytes and fat bodies of infected larvae were compared with those of aseptically injured larvae. Our analysis included the construction of protein maps of the hemocyte cells and cells from fat bodies, the identification of the changed proteins, in response to infection, using LC-MS/MS, and the estimation of the trends in expression of these proteins at three time points (30 min, 6 hours and 22 hours) after infection. In total, seven changed spots were found in the hemocytes, and four changed spots were found in the fat bodies. Three types of trends in protein expression were observed. Cofilin and transgelin were undetectable at 30 min after infection but were continuously up-regulated in the induced larvae after 22 hours. A prophenoloxidase isoform and lectin subunit α were slightly up-regulated at 30 min after infection, and their protein levels reached the highest points after 6 hours but decreased after 22 hours. T-Complex subunit α, GST, ferritin-like protein and an anterior fat body protein (regucalcin homologue) were down-regulated at 22 hours after infection.

Conclusions

Many proteins identified in our study corresponded to the proteins identified in other insects. Compared to the former studies performed in insects, we presented 2-D protein maps of the hemocytes and fat bodies and showed the trends in expression of the immune-elicited proteins.

A genome-wide survey for host response of silkworm, Bombyx mori during pathogen Bacillus bombyseptieus infection

Host-pathogen interactions are complex relationships, and a central challenge is to reveal the interactions between pathogens and their hosts. Bacillus bombysepticus (Bb) which can produces spores and parasporal crystals was firstly separated from the corpses of the infected silkworms (Bombyx mori). Bb naturally infects the silkworm can cause an acute fuliginosa septicaemia and kill the silkworm larvae generally within one day in the hot and humid season. Bb pathogen of the silkworm can be used for investigating the host responses after the infection. Gene expression profiling during four time-points of silkworm whole larvae after Bb infection was performed to gain insight into the mechanism of Bb-associated host whole body effect. Genome-wide survey of the host genes demonstrated many genes and pathways modulated after the infection. GO analysis of the induced genes indicated that their functions could be divided into 14 categories. KEGG pathway analysis identified that six types of basal metabolic pathway were regulated, including genetic information processing and transcription, carbohydrate metabolism, amino acid and nitrogen metabolism, nucleotide metabolism, metabolism of cofactors and vitamins, and xenobiotic biodegradation and metabolism. Similar to Bacillus thuringiensis (Bt), Bb can also induce a silkworm poisoning-related response. In this process, genes encoding midgut peritrophic membrane proteins, aminopeptidase N receptors and sodium/calcium exchange protein showed modulation. For the first time, we found that Bb induced a lot of genes involved in juvenile hormone synthesis and metabolism pathway upregulated. Bb also triggered the host immune responses, including cellular immune response and serine protease cascade melanization response. Real time PCR analysis showed that Bb can induce the silkworm systemic immune response, mainly by the Toll pathway. Anti-microorganism peptides (AMPs), including of Attacin, Lebocin, Enbocin, Gloverin and Moricin families, were upregulated at 24 hours post the infection.