Identification and phylogenetic analysis on lipopolysaccharide and beta-1,3-glucan binding protein (LGBP) of kuruma shrimp Marsupenaeus japonicus

Role of Cellular Receptors in the Innate Immune System of Crustaceans in Response to White Spot Syndrome Virus

Innate immunity is the only defense system for resistance against infections in crustaceans. In crustaceans, white spot diseases caused by white spot syndrome virus (WSSV) are a serious viral disease with high accumulative mortality after infection. Attachment and entry into cells have been known to be two initial and important steps in viral infection. However, systematic information about the mechanisms related to WSSV infection in crustaceans is still limited. Previous studies have reported that cellular receptors are important in the innate immune system and are responsible for the recognition of foreign microorganisms and in the stimulation of the immune responses during infections. In this review, we summarize the current understanding of the functions of cellular receptors, including Toll, C-type lectin, scavenger receptor, β-integrin, polymeric immunoglobulin receptor, laminin receptor, globular C1q receptor, lipopolysaccharide-and β-1,3-glucan-binding protein, chitin-binding protein, Ras-associated binding, and Down syndrome cell adhesion molecule in the innate immune defense of crustaceans, especially shrimp and crabs, in response to WSSV infection. The results of this study provide information on the interaction between viruses and hosts during infections, which is important in the development of preventative strategies and antiviral targets in cultured aquatic animals.

Crustacean Hemolymph Lipoproteins

Lipoproteins mediate the transport of apolar lipids in the hydrophilic environment of physiological fluids such as the vertebrate blood and the arthropod hemolymph. In this overview, we will focus on the hemolymph lipoproteins in Crustacea that have received most attention during the last years: the high density lipoprotein/β-glucan binding proteins (HDL-BGBPs), the vitellogenins (VGs), the clotting proteins (CPs) and the more recently discovered large discoidal lipoproteins (dLPs). VGs are female specific lipoproteins which supply both proteins and lipids as storage material for the oocyte for later use by the developing embryo. Unusual within the invertebrates, the crustacean yolk proteins-formerly designated VGs-are more related to the ApoB type lipoproteins of vertebrates and are now termed apolipocrustaceins. The CPs on the other hand, which are present in both sexes, are related to the (sex specific) VGs of insects and vertebrates. CPs serve in hemostasis and wound closure but also as storage proteins in the oocyte. The HDL-BGBPs are the main lipid transporters, but are also involved in immune defense. Most crustacean lipoproteins belong to the family of the large lipid transfer proteins (LLTPs) such as the intracellular microsomal triglyceride transfer protein, the VGs, CPs and the dLPs. In contrast, the HDL-BGBPs do not belong to the LLTPs and their relationship with other lipoproteins is unknown. However, they originate from a common precursor with the dLPs, whose functions are as yet unknown. The majority of lipoprotein studies have focused on decapod crustaceans, especially shrimps, due to their economic importance. However, we will present evidence that the HDL-BGBPs are restricted to the decapod crustaceans which raises the question as to the main lipid transporting proteins of the other crustacean groups. The diversity of crustaceans lipoproteins thus appears to be more complex than reflected by the present state of knowledge.

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.

Alginate from Sargassum siliquosum Simultaneously Stimulates Innate Immunity, Upregulates Immune Genes, and Enhances Resistance of Pacific White Shrimp (Litopenaeus vannamei) Against White Spot Syndrome Virus (WSSV)

Although alginate is known as an immunostimulant in shrimp, the comprehensive and simultaneous study on its activity to resolve the relationship of the hematological parameters, upregulation of immune-related gene expression, and resistance to pathogen has not been found in shrimp. We performed experiments to evaluate the effect and mechanism of alginate from S. siliquosum on Pacific white shrimp immune system. Hematological parameters were examined after oral administration of Na alginate in the shrimp. White spot syndrome virus (WSSV) was injected to the shrimp at 14 days, and its copy number was examined quantitatively (qRT-PCR). Immune-related gene expression was evaluated by qRT-PCR. Alginate increased some hematological immune parameters of shrimp. Before WSSV infection, expression levels of Toll and lectin genes were upregulated. The lectin gene were upregulated post infection, and the Toll gene in all the treatments were downregulated, except the shrimps fed with alginate at 6.0 g kg-1 at 48 h post infection (hpi). The shrimps fed with alginate at 6.0 g kg-1 were the most resistant and gave the least WSSV copy number at 48 hpi. Resistance of shrimps fed the alginate-supplemented diets against WSSV was significantly higher compared to that of the control treatment with 56% and 10% of survival rates, respectively. Oral administration of alginate did not affect the growth and total protein plasma. At 120 h post challenge, alginate treatment at 6.0 g kg-1 exhibited the highest survival rate. It is concluded that oral administration of alginate enhanced the innate immunity by upregulating immune-related gene expression. Consequently, the enhancement of the shrimp innate immunity improves the resistance against WSSV infection.

The effect of Spirulina platensis meal on antioxidant gene expression, total antioxidant capacity, and lipid peroxidation of rainbow trout (Oncorhynchus mykiss)

The study was conducted to investigate the effect of diets containing 0, 2.5, 5, 7.5, and 10% S. platensis meal on total antioxidant capacity (TAC) and lipid peroxidation, as well as the expression of two antioxidant enzyme genes (SOD and CAT) in rainbow trout (Oncorhynchus mykiss). One hundred and eighty fish, with an average initial weight of 101 ± 8 g, were cultured for 10 weeks. At the end of experiment, lipid peroxidation significantly decreased in serum of fish fed with S. platensis and fish fed with 5, 7.5, and 10% microalgae showed a significantly lower value compared to control and 2.5%. Inclusion of 7.5 and 10% S. platensis in diet also decreased lipid peroxidation in liver. TAC significantly increased with increasing level of S. platensis. Expression level of superoxide dismutase (SOD) and catalase (CAT) genes significantly increased in the fish liver after administration of microalgae and fish fed with 10% S. platensis in diet showed the highest level compared to the other treatments. The present study reveals that inclusion of 10% S. platensis in diet can decrease oxidative stress in rainbow trout. Therefore, S. platensis can be used as potential antioxidant for fish farming.

Comparative transcriptomic analysis of Marsupenaeus japonicus hepatopancreas in response to Vibrio parahaemolyticus and white spot syndrome virus

Vibrio parahaemolyticus and white spot syndrome virus (WSSV) are pathogens that cause epidemics in kuruma shrimp (Marsupenaeus japonicus) during aquaculture, resulting in severe economic losses to local farmers. To characterise the mechanisms of the molecular responses to V. parahaemolyticus and WSSV infection in M. japonicus, the transcriptome of hepatopancreas was sequenced using next-generation sequencing after infection. A total of 29,180 unigenes were assembled, with an average length of 1,151 bp (N50 = 1,951 bp). After BLASTX searching against the Nr database (E-value cut-off = 10^-5), 15,176 assembled unigenes remained, with 3,039 and 1,803 differentially expressed transcripts identified in the V. parahaemolyticus- and WSSV-infected groups, respectively. Of these, 1466 transcripts were up-regulated and 1573 were down-regulated in V. parahaemolyticus-infected shrimps, and 970 transcripts were up-regulated and 833 were down-regulated in the WSSV-infected shrimps. Additionally, 761 transcripts were differentially expressed in both V. parahaemolyticus- and WSSV-infected shrimps. Several known immune-related genes including caspase 4, integrin, crustin, ubiquitin-conjugating enzyme E2, C-type lectin, and α₂-macroglobulin were among the differentially expressed transcripts. These results provide valuable information for characterising the immune mechanisms of the shrimp responses of to V. parahaemolyticus andWSSV infection.

Effects of dietary Bacillus subtilis and Shewanella algae in expression profile of immune-related genes from hemolymph of Litopenaeus vannamei challenged with Vibrio parahaemolyticus

B. subtilis and S. algae effects in growth, survival and innate immunity were assessed on L. vannamei juveniles. During 60 days, shrimp were reared in three treatments: Bs, fed with 10⁶ CFU of B. subtilis per gram of commercial feed, Sa, fed with 10⁶ CFU of S. algae per gram of commercial feed and Control (without bacterial addition). Then, the animals were subjected to a V. parahaemolyticus challenge. For this purpose, four treatments were established: Control (shrimp not submitted to probiotic treatments), Vibrio (Vibrio challenged shrimp), Vibrio + Bs (Bs challenged shrimp) and Vibrio + Sa (Sa challenged shrimp). Shrimp hemolymph was sampled 45-days after rearing and 24 h post-challenge for quantification of prophenoloxidase (proPO), lipopolysaccharide and β-1,3-glucan-binding protein (LGBP) and hemocyanin (HEM) transcripts by qPCR. Moreover, shrimp final weight and survival were also verified. B. subtilis administration enhanced shrimp growth and improved proPO, LGBP and HEM expression levels before and after challenge. After 60-days of feeding, Sa final weight was higher than the Control, whereas Vibrio + Sa cumulative mortality after 48 h of Vibrio challenge was lower than Vibrio group. These results could be correlated with the proPO and LGBP up regulation in Vibrio + Sa compared to Vibrio group, protecting L. vannamei from the bacterial infection. Together, these results suggest the probiotic potential of B. subtilis e S. algae in the modulation of immune-related genes as a tool to control V. parahaemolyticus infection inside shrimp.

Expression of Macrobrachium rosenbergii lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) in Saccharomyces cerevisiae and evaluation of its immune function

Pattern recognition proteins (PRPs) activate the innate immune system in invertebrates, and lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) is an important PRP with various biological functions. Here, the open reading frame (ORF) of Macrobrachium rosenbergii LGBP (MrLGBP) was cloned into plasmid vector pHAC181, then integrated into downstream of the GAL1 promoter of Saccharomyces cerevisiae strain GAL1-ScRCH1 via homologous recombination, followed by its expression in the yeast eukaryotic system. The resulting recombinant LGBP contained a 3 × HA-tag at its C terminus and had a molecular weight of about 45 kDa, as evaluated by western blot analysis. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were ranged from 0.340 to 0.802 and 1.189-1.810 μM, respectively. The recombinant MrLGBP protein agglutinated almost all tested bacteria except Bacillus thuringiensis and Staphylococcus aureus. These results revealed that this recombinant protein exhibited antimicrobial activity against some Gram-positive and Gram-negative bacteria. M. rosenbergii prawns were fed with the recombinant yeast strain MrLGBP for 1 month and challenged with the most common crustacean pathogen, Vibrio parahaemolyticus. These prawns showed lower mortality and higher enzymatic activity and expression levels of immunity genes than did the control groups. All these results suggest that MrLGBP may play important roles in the innate immunity of crustaceans, and recombinant strain S. cerevisiae MrLGBP may be useful for the development of an effective immune feed additive in the future.

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.

A synbiotic improves the immunity of white shrimp, Litopenaeus vannamei: Metabolomic analysis reveal compelling evidence

In this study, we examined the synergistic effects of a diet-administered synbiotic comprising galactooligosaccharide (GOS) and the probiotic Lactobacillus plantarum 7-40 on immune responses, immune-related gene expressions, and disease resistance to Vibrio alginolyticus in white shrimp Litopenaeus vannamei. To unravel the regulatory role of the synbiotic in activating the immune system of shrimp, ¹H nuclear magnetic resonance (NMR)-based metabolomic analysis were used to investigate hepatopancreas metabolites, then significantly altered metabolites were confirmed in both the hepatopancreas and plasma by reverse-phase high-performance liquid chromatography (RP-HPLC) and spectrophotometric analysis. Shrimp were fed four experimental diets for 60 days, including a basal diet with no GOS or probiotic (control), 0.4% GOS (PRE), probiotic (PRO), and 0.4% GOS in combination with the probiotic (SYN). Results showed that the SYN diet significantly increased survival of L. vannamei 24 h after a V. alginolyticus injection. Immune parameters such as phenoloxidase activity, respiratory bursts, phagocytic activity and gene expressions, including prophenoloxidase I, serine proteinase, and peroxinectin, of shrimp fed the SYN diet significantly increased, compared to the other treatments and control. In addition, results from the ¹H NMR analysis revealed that 22 hepatopancreas metabolites were matched and identified between the SYN and control groups, among which three metabolites, i.e., inosine monophosphate (IMP), valine, and betaine, significantly increased in the SYN group. Confirmation using RP-HPLC and spectrophotometric methods showed that IMP presented high amounts in the hepatopancreas, but not in the plasma of shrimp; in contrast, valine and betaine metabolites were in high concentrations in both the hepatopancreas and plasma. Our results suggested that GOS and the probiotic had a synergistic effect on enhancing immunity and disease resistance of L. vannamei against V. alginolyticus infection through inducing syntheses of a nucleotide (IMP), a branched amino acid (valine), and a methyl group donor (betaine) in the hepatopancreas, which were then released into the plasma and directly taken up by hemocytes, resulting in a triggering of melanization and phagocytosis processes in cells.

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.

β-1,3-Glucan recognition protein 3 activates the prophenoloxidase system in response to bacterial infection in Ostrinia furnacalis Guenée

Pattern recognition receptors (PRRs) are biosensor proteins that bind to non-self pathogen associated molecular patterns (PAMPs). β-1,3-glucan recognition proteins (βGRPs) play an essential role in immune recognition and signaling pathway of insect innate immunity. Here, we report the cloning and characterization of cDNA of OfβGRP3 from Ostrinia furnacalis larvae. The OfβGRP3 contains 1455 bp open reading frame, encoding a predicted 484 amino acid residue protein. In hemocytes, the expression levels of OfβGRP3 in Escherichia coli-challenged group were higher than those of Bacillus subtilis-challenged group at 2, 4, 8, 10 and 12 h post injection (HPI). In fat body, OfβGRP3 expression in both B. subtilis and E. coli-challenged group was significantly higher than that in untreated group from 4 to 10 HPI, and then the expression continuously dropped from 12 to 36 HPI. The OfβGRP3 expression in laminarin-injected group was higher than that in lipopolysaccharides (LPS)-injected group in various test tissues from 4 to 24 HPI. The LT₅₀ of E. coli-infected OfβGRP3-RNAi larvae (1.0 days) was significantly lower compared with that of E. coli infected wild-type larvae (3.0 days) (p < 0.01). Only 10.2% Sephadex G50 beads (degree 3) were completely melanized in the larvae inoculated with OfβGRP3 dsRNA, as compared to 48.8% in control larvae (p < 0.01). A notable reduction in the PO activity and IEARase activity in hemolymph was also detected in the OfβGRP3 knockdown larvae. Our study demonstrates that OfβGRP3 is one of PRR members involved the PPO-activating system in O. furnacalis larvae.

Various cellular responses of different shrimp haemocyte subpopulations to lipopolysaccharide stimulation

Different haemocyte types have been reported to play diverse roles in immune defense of shrimp. To investigate the roles of the three haemocyte types [hyaline cells (HC), semigranular cells (SGC) and granular cells (GC)] of shrimp in immune responses against lipopolysaccharide (LPS), percentage, non-specific esterase activity (EA), reactive oxygen species (ROS) production and nitric oxide (NO) production of the three haemocyte subpopulations were analyzed in LPS-injected Penaeus monodon using flow cytometry. Results showed that percentage of HC increased after 3 h injection, and returned to the original level after 48 h. Proportion of SGC and GC reduced after 6-36 h and 3-12 h respectively, and recovered to the initial level after 48 and 24 h respectively. Loss of SGC and GC might be related to degranulation to release proPO system, and degranulation of GC seemed more sensitive to LPS stimulation. EA of both HC and SGC improved after 3-6 h injection, while EA of GC was induced after 3-24 h. No significant effect of LPS injection could be found in ROS production and NO production of HC. Enhanced ROS levels was observed in SGC and GC after 3-24 h and 3-36 h respectively, and NO production of SGC and GC improved after 3-48 h injection. These results demonstrated that SGC and GC possessed strong capabilities for LPS-induced EA, ROS production and NO production, while HC only displayed EA response to LPS, suggesting that GC and SGC play the main role in immune defense of shrimp against Gram-negative bacteria.

Comparative genomic analysis of innate immunity reveals novel and conserved components in crustacean food crop species

BACKGROUND

Growing global demands for crustacean food crop species have driven large investments in aquaculture research worldwide. However, large-scale production is susceptible to pathogen-mediated destruction particularly in developing economies. Thus, a thorough understanding of the immune system components of food crop species is imperative for research to combat pathogens.

RESULTS

Through a comparative genomics approach utilising extant data from 55 species, we describe the innate immune system of the class Malacostraca, which includes all food crop species. We identify 7407 malacostracan genes from 39 gene families implicated in different aspects of host defence and demonstrate dynamic evolution of innate immunity components within this group. Malacostracans have achieved flexibility in recognising infectious agents through divergent evolution and expansion of pathogen recognition receptors genes. Antiviral RNAi, Toll and JAK-STAT signal transduction pathways have remained conserved within Malacostraca, although the Imd pathway appears to lack several key components. Immune effectors such as the antimicrobial peptides (AMPs) have unique evolutionary profiles, with many malacostracan AMPs not found in other arthropods. Lastly, we describe four putative novel immune gene families, potentially representing important evolutionary novelties of the malacostracan immune system.

CONCLUSION

Our analyses across the broader Malacostraca have allowed us to not only draw analogies with other arthropods but also to identify evolutionary novelties in immune modulation components and form strong hypotheses as to when key pathways have evolved or diverged. This will serve as a key resource for future immunology research in crustacean food crops.

Lipopolysaccharide- and β-1,3-glucan-binding protein from Fenneropenaeus merguiensis functions as a pattern recognition receptor with a broad specificity for diverse pathogens in the defense against microorganisms

In crustaceans, lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) plays an important role in innate immunity by mediating the recognition of pathogens to host cells. Hereby, LGBP was cloned from Fenneropenaeus merguiensis hepatopancreas. Its full-length cDNA (1280 bp) had an open reading frame of 1101 bp, encoding a peptide of 366 amino acids. The LGBP primary structure comprises a recognition motif for β-1,3-linkage of polysaccharides, two integrin binding motifs, a kinase C phosphorylation site and a bacterial glucanase motif. The LGBP mRNA was strongly expressed in hepatopancreas and significantly up-regulated to get the maximum at 12 h upon Vibrio harveyi challenge. Recombinant LGBP (rLGBP) could agglutinate Gram-negative and Gram-positive bacteria including yeast with Ca²⁺-dependence. V. harveyi agglutination induced by rLGBP was intensively inhibited by lipoteichoic acid, less in order were lipopolysaccharide, β-1,3-glucan and N-acetyl neuraminic acid. Western blotting revealed that rLGBP bound widely to Gram-negative and Gram-positive bacteria and also yeast. By ELISA quantification, rLGBP could bind to β-1,3-glucan better than to lipopolysaccharide and lipoteichoic acid. These findings suggest that LGBP may function as a receptor which recognizes invading diverse pathogens and contribute in F. merguiensis immune response.

Antimicrobial and Antitumor Activities of Novel Peptides Derived from the Lipopolysaccharide- and β-1,3-Glucan Binding Protein of the Pacific Abalone Haliotis discus hannai

Antimicrobial peptides are a pivotal component of the invertebrate innate immune system. In this study, we identified a lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) gene from the pacific abalone Haliotis discus hannai (HDH), which is involved in the pattern recognition mechanism and plays avital role in the defense mechanism of invertebrates immune system. The HDH-LGBP cDNA consisted of a 1263-bp open reading frame (ORF) encoding a polypeptide of 420 amino acids, with a 20-amino-acid signal sequence. The molecular mass of the protein portion was 45.5 kDa, and the predicted isoelectric point of the mature protein was 4.93. Characteristic potential polysaccharide binding motif, glucanase motif, and β-glucan recognition motif were identified in the LGBP of HDH. We used its polysaccharide-binding motif sequence to design two novel antimicrobial peptide analogs (HDH-LGBP-A1 and HDH-LGBP-A2). By substituting a positively charged amino acid and amidation at the C-terminus, the pI and net charge of the HDH-LGBP increased, and the proteins formed an α-helical structure. The HDH-LGBP analogs exhibited antibacterial and antifungal activity, with minimal effective concentrations ranging from 0.008 to 2.2 μg/mL. Additionally, both were toxic against human cervix (HeLa), lung (A549), and colon (HCT 116) carcinoma cell lines but not much on human umbilical vein cell (HUVEC). Fluorescence-activated cell sorter (FACS) analysis showed that HDH-LGBP analogs disturb the cancer cell membrane and cause apoptotic cell death. These results suggest the use of HDH-LGBP analogs as multifunctional drugs.

White shrimp Litopenaeus vannamei that have received fucoidan exhibit a defense against Vibrio alginolyticus and WSSV despite their recovery of immune parameters to background levels

White shrimp Litopenaeus vannamei receiving fucoidan at 2, 6, and 10 μg g^-1 after 0-144 h or 0-120 h were examined for immune parameters (haemograms, phenoloxidase activity, respiratory burst, and superoxide dismutase activity), proliferation of haemocyte in the haematopoietic tissue (HPT), gene expression, and phagocytic activity and clearance efficiency to Vibrio alginolyticus. Immune parameters and mitotic index of HPT increased after 3-24 h, reached their maxima after 48-72 h, and returned to background values after 144 h. Transcripts of lipopolysaccharide and β-1,3-glucan binding protein (LGBP), peroxinectin (PX), prophenoloxidase (proPO) I, proPO II, astakine, and haemocyte homeostasis-associated protein (HHAP) were up-regulated to a maximum after 48-72 h and returned to background values after 144 h. Phagocytic activity and clearance efficiency to V. alginolyticus increased after 12 h, reached its maximum after 48 h, and continued to remain higher after 120 h. In another experiment, shrimp receiving fucoidan after 48 h and 144 h were respectively challenged with V. alinolyticus at 6 × 10⁶ colony-forming units (cfu) shrimp^-1 or challenged with WSSV at 1.2 × 10⁵ copies shrimp^-1 and then placed in seawater. The survival rate of shrimp receiving fucoidan was significantly higher than in controls. In conclusion, shrimp receiving fucoidan showed a proliferation of HPT, increased immune parameters, and up-regulated transcripts of LGBP, PX, proPO I, proPO II, astakine, and HHAP after 48 h. Shrimp receiving fucoidan exhibited a defense against V. alginolyticus and WSSV, even after immune parameters recovered to background levels.

Spirulina elicits the activation of innate immunity and increases resistance against Vibrio alginolyticus in shrimp

The effect of Spirulina dried powder (SDP) on the immune response of white shrimp Litopenaeus vannamei was studied in vitro and in vivo. Incubating shrimp haemocytes in 0.5 mg ml(-1) SDP caused the degranulation of haemocytes and a reduction in the percentage of large cells within 30 min. Shrimp haemocytes incubated in 1 mg ml(-1) SDP significantly increased their phenoloxidase (PO) activity, serine proteinase activity, and respiratory burst activity (RB, release of superoxide anion). A recombinant protein of lipopolysaccharide and β-1,3-glucan binding protein (LGBP) of the white shrimp was produced, named rLvLGBP, and examined for its binding with SDP. An ELISA binding assay showed that rLvLGBP binds to SDP with a dissociation constant of 0.0507 μM. In another experiment, shrimp fed diets containing SDP at 0 (control), 30, and 60 g kg(-1) after four weeks were examined for LGBP transcript level and lysozyme activity, as well as phagocytic activity, clearance efficiency, and resistance to Vibrio alginolyticus. These parameters were significantly higher in shrimp receiving diets containing SDP at 60 g kg(-1) or 30 g kg(-1) than in controls. In conclusion, shrimp haemocytes receiving SDP provoked the activation of innate immunity as evidenced by the recognition and binding of LGBP, degranulation of haemocytes, reduction in the percentage of large cells, increases in PO activity, serine proteinase activity, superoxide anion levels, and up-regulated LGBP transcript levels. Shrimp receiving diets containing SDP had increased lysozyme activity and resistance against V. alginolyticus infection. This study showed the mechanism underlying the immunostimulatory action of Spirulina and its immune response in shrimp.

Lipopolysaccharide and beta-1, 3-glucan binding protein (LGBP) stimulates prophenoloxidase activating system in Chinese mitten crab (Eriocheir sinensis)

Melanization mediated by prophenoloxidase (proPO) activating system play an essential role in killing invading microorganisms in invertebrates. Lipopolysaccharide and β-1, 3-glucan binding protein (LGBP) as a pattern recognition protein have been demonstrated to active the proPO cascade in insect and shrimp. In this study, we investigated the role of LGBP in prophenoloxidase cascade-induced melanization in Chinese mitten crab (Eriocheir sinensis). By RT-PCR analysis, EsLGBP was detected in all tested tissues, and showed highest expression in hemocytes, gill, intestine and brain. The expression of EsLGBP was up-regulated in the hemocytes following injections of LPS and β-1, 3-glucan. The recombinant EsLGBP protein (rEsLGBP) was produced via prokaryotic expression system and affinity chromatography. By western blotting, rEsLGBP was discovered to exhibit the ability to bind to all tested microorganisms, including Gram-negative bacteria, Gram-positive bacteria and yeast (Pichia pastoris). Meanwhile we found rEsLGBP has a high binding activity towards microbial immune elicitors such as LPS and β-1, 3-glucan whereas no binding activity is detected with peptidoglycan. Moreover, the effects of RNAi-mediated blockade of EsLGBP were investigated on bacterial counts in the hemolymph and cumulative mortality rate of crabs infected with Vibrio parahaemolyticus in vivo. Further experiments demonstrate that rEsLGBP can trigger the whole hemolymph dependent melanization and stimulate to proPO cascade in vitro. Taken together, these results provide experimental evidence for role of LGBP in innate immunity, especially in the activation of prophenoloxidase activating system.

Lipopolysaccharide and β-1,3-glucan-binding protein (LGBP) bind to seaweed polysaccharides and activate the prophenoloxidase system in white shrimp Litopenaeus vannamei

Lipopolysaccharide and β-1,3-glucan-binding protein (LGBP), important pattern recognition proteins (PRPs), recognize lipopolysaccharide (LPS) and β-1,3-glucan (βG), known as pathogen-associated molecular patterns (PAMPs), and subsequently trigger innate immunity. Several seaweed polysaccharides and seaweed extracts increase immune parameters and resistance to pathogens. Here, we constructed the expression vector pET28b-LvLGBP and transferred it into Escherichia coli BL21 (DE3) for protein expression and to produce the recombinant protein LGBP (rLvLGBP) in white shrimp Litopenaeus vannamei. We examined the binding of rLvLGBP with seaweed-derived polysaccharides including alginate, carrageenan, fucoidan, laminarin, Gracilaria tenuistipitata extract (GTE), and Sargassum duplicatum extract (SDE), and examined the phenoloxidase activity of shrimp haemocytes incubated with a mixture of rLvLGBP and each polysaccharide. We also examined the binding of rLvLGBP with LPS and βG, and the phenoloxidase activity of shrimp haemocytes incubated with a mixture of rLvLGBP and LPS (rLvLGBP-LPS) or a mixture of rLvLGBP and βG (rLvLGBP-βG). An ELISA binding assay indicated that rLvLGBP binds to LPS, βG, alginate, carrageenan, fucoidan, laminarin, GTE, and SDE with dissociation constants of 0.1138-0.1770 μM. Furthermore, our results also indicated that the phenoloxidase activity of shrimp haemocytes incubated with a mixture of rLvLGBP and LPS, βG, alginate, carrageenan, fucoidan, laminarin, GTE, and SDE significantly increased by 328%, 172%, 200%, 213%, 197%, 194%, 191%, and 197%, respectively compared to controls (cacodylate buffer). We conclude that LvLGBP functions as a PRP, recognizes and binds to LPS, βG, alginate, carrageenan, fucoidan, laminarin, GTE, and SDE, and subsequently leads to activating innate immunity in shrimp.

Sulfated galactans from Gracilaria fisheri bind to shrimp haemocyte membrane proteins and stimulate the expression of immune genes

Previous studies demonstrated that sulfated galactans (SG) from Gracilaria fisheri (G. fisheri) exhibit immunostimulant activity in shrimp. The present study was conducted to test the hypothesis that SG stimulates signaling molecules of the immune response of shrimp by binding to receptors on the host cell membrane. Accordingly, we evaluated the ability of SG to bind to shrimp haemocytes and showed that SG bound to the shrimp haemocyte membrane (SHM), potentially to specific receptors. Furthermore, this binding was associated with an activation of immune response genes of shrimp. Data from confocal laser scanning micrographs revealed that FITC-labeled SG bound to haemocytes. Far western blot analysis demonstrated that SHM peptides, with molecular sizes of 13, 14, 15, 17, and 25 kDa, were associated with SG. Peptide sequence analysis of the isolated bands using LC-MS/MS and NCBI blast search revealed the identity of the 13, 14, and 17 kDa peptides as lipopolysaccharide and β-1,3-glucan binding protein (LGBP). SG induced the expression of immune related genes and downstream signaling mediators of LGBP including IMD, IKKs, NF-κB, antimicrobial peptides (crustin and PEN-4), the antiviral immunity (dicer), and proPO system (proPO-I and proPO-II). A LGBP neutralizing assay with anti-LGBP antibody indicated a decrease in SG-induced expression of LGBP downstream signaling mediators and the immune related genes. In conclusion, this study demonstrated that the SG-stimulated immune activity in haemocytes is mediated, in part, through the LGBP, and IMD-NF-κB pathway.

White Shrimp Litopenaeus vannamei That Have Received Gracilaria tenuistipitata Extract Show Early Recovery of Immune Parameters after Ammonia Stressing

White shrimp Litopenaeus vannamei immersed in seawater (35‰) containing Gracilaria tenuistipitata extract (GTE) at 0 (control), 400, and 600 mg/L for 3 h were exposed to 5 mg/L ammonia-N (ammonia as nitrogen), and immune parameters including hyaline cells (HCs), granular cells (GCs, including semi-granular cells), total hemocyte count (THC), phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, lysozyme activity, and hemolymph protein level were examined 24~120 h post-stress. The immune parameters of shrimp immersed in 600 mg/L GTE returned to original values earlier, at 96~120 h post-stress, whereas in control shrimp they did not. In another experiment, shrimp were immersed in seawater containing GTE at 0 and 600 mg/L for 3 h and examined for transcript levels of immune-related genes at 24 h post-stress. Transcript levels of lipopolysaccharide and β-1,3-glucan binding protein (LGBP), peroxinectin (PX), cytMnSOD, mtMnSOD, and HSP70 were up-regulated at 24 h post-stress in GTE receiving shrimp. We concluded that white shrimp immersed in seawater containing GTE exhibited a capability for maintaining homeostasis by regulating cellular and humoral immunity against ammonia stress as evidenced by up-regulated gene expression and earlier recovery of immune parameters.

Dietary administration of Gynura bicolor (Roxb. Willd.) DC water extract enhances immune response and survival rate against Vibrio alginolyticus and white spot syndrome virus in white shrimp Litopeneaus vannamei

Gynura bicolor (Roxb. & Willd.) DC., a perennial plant belonging to the Asteraceae family, is originated from the tropical area of Asia. The total hemocyte count (THC), phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, and lysozyme activity were examined after white shrimp Litopenaeus vannamei had been fed diets containing the water extract of G. bicolor at 0 (control), 0.5, 1.0, and 2.0 g (kg diet)(-1) for 7-28 days. The results indicated that these parameters increased accordingly with the amount of extract and time. THCs of the shrimp fed the G. bicolor diets at 1.0 and 2.0 g (kg diet)(-1) were significantly higher than that fed the control diet for 14-28 days. For the shrimp fed the G. bicolor diets at 0.5, 1.0, and 2.0 g (kg diet)(-1), the PO, RBs, and lysozyme activities reached the highest levels after 7 days, whereas SOD activity reached the highest levels after 14 days. In a separate experiment, white shrimp L. vannamei fed the diets containing the G. bicolor extract for 28 days were challenged with Vibrio alginolyticus at 3 × 10(6) cfu shrimp(-1) and white spot syndrome virus (WSSV) at 1 × 10(3) copies shrimp(-1). The survival rate of the shrimp fed the G. bicolor diets was significantly higher than that of the shrimp fed the control diet at 48-144 h post challenge V. alginolyticus and WSSV. For the shrimp fed the G. bicolor diets at 0.5, 1 and 2 g (kg diet)(-1) under challenges of V. alginolyticus and WSSV, their LPS- and β-1,3-glucan-binding protein (LGBP) and peroxinectin (PE) mRNA expressions were significantly higher than those of the challenged control shrimp at 12-96 and 24-144 h post-challenge, respectively. We concluded that dietary administration of a G. bicolor extract could enhance the innate immunity within 28 days as evidenced by the increases in immune parameters (PO, RBs, and lysozyme) and antioxidant enzyme (SOD) activities of shrimp to against V. alginolyticus and WSSV infections.

PtLGBP, a pattern recognition receptor in Portunus trituberculatus involved in the immune response against different challenges

Lipopolysaccharide and b-1,3-glucan binding protein (LGBP) is a pattern recognition receptor that can recognize and bind LPS and b-1,3-glucan. LGBP has crucial roles in innate immune defense against Gram-negative bacteria and fungi. In this study, LGBP functions in Portunus trituberculatus innate immunity were analyzed. First, the mRNA expression of PtLGBP in hemocytes, hepatopancreas, and muscle toward three typical pathogen-associated molecular patterns (PAMPs) stimulations were examined using real-time PCR. Results show that the overall trend of relative expressions of the LGBP gene in three tissues is consistent, showing up-down trend. In each group, the highest expression of the LGBP gene was at 3 and 12 h post-injection. The LGBP gene is also expressed significantly higher in the hemocytes and hepatopancreas than in the muscle. The highest level of LGBP was in the lipopolysaccharides (LPS) and glucan-injected group, whereas the lowest level was in the PGN-injected group. Furthermore, bacterial agglutination assay with polyclonal antibody specifically for PtLGBP proved that the recombinant PtLGBP (designated as rPtLGBP) could exhibit obvious agglutination activity toward Gram-negative bacteria Escherichia coli, Vibrio parahaemolyticus, and V. alginolyticus; Gram-positive bacteria Bacillus subtilis; and fungi Saccharomyces cerevisiae. LGBP in Portunus trituberculatus possibly served as a multi-functional PRR. In addition, LGBP is not only involved in the immune response against Gram-negative and fungi, as manifested in other invertebrates, but also has a significant role in anti-Gram-positive bacteria infection.

Dietary effect of Sargassum wightii fucoidan to enhance growth, prophenoloxidase gene expression of Penaeus monodon and immune resistance to Vibrio parahaemolyticus

The polysaccharide fucoidan from brown seaweed Sargassum wightii was extracted and it was incorporated with pellet diets at three concentrations (0.1, 0.2 & 0.3%). The fucoidan incorporated diets were fed to shrimp Penaeus monodon for 60 days and the growth performance was assessed. The weight gain and SGR of control group was 6.83 g and 9.72%, respectively, but the weight gain and SGR of various concentrations (0.1-0.3%) of fucoidan incorporated diets fed groups of shrimp was increased from 7.30 to 8.20 g and 9.83 to 10.03%, respectively. After 60 days of feeding experiment, the relative quantification of prophenoloxidase gene of experimental groups over control group was analysed by RT-PCR and it was ranged between 2.13 and 7.95 fold increase within 33.52-34.61 threshold cycles, respectively at 0.1-0.3% concentrations of fucoidan. After 60 days of feeding experiment, the P. monodon were challenged with shrimp pathogen Vibrio parahaemolyticus and the mortality percentage was recorded daily up to 21 days. The reduction in mortality percentage of experimental groups over control group was recorded from 44.56 to 72.79%, respectively in 0.1-0.3% of fucoidan incorporated diets fed groups. During challenge experiment, all the immunological parameters such as THC, prophenoloxidase activity, respiratory burst activity, superoxide dismutase activity, phagocytic activity, bactericidal activity and bacterial clearance ability of experimental groups were significantly (P < 0.05) increased than control group. The V. parahaemolyticus load was enumerated from the infected shrimp at every 10 days intervals during challenge experiment. In control group, the Vibrio load was increased in hepatopancreas and muscle tissues from 10th to 21st days of challenge test. But in the experimental groups, the Vibrio load in both the tissues decreased positively from 10th to 21st days of challenge duration. It is concluded that the S. wightii fucoidan had enhanced the innate immunity and increased resistance to V. parahaemolyticus infection in P. monodon.

Purification, characterization and functional analysis of a novel β-1, 3-glucan binding protein from green tiger shrimp Penaeus semisulcatus

A β-1, 3-Glucan binding protein (β-GBP) was isolated from green tiger shrimp Penaeus semisulcatus and purified using laminarin precipitation and affinity chromatography on laminarin-Sepharose 6B column respectively. P. semisulcatus β-GBP exhibits a single band with a molecular weight of 112 kDa on SDS-PAGE and pI of 5.9 in isoelectric focusing (IEF). Negative staining of P. semisulcatus β-GBP showed large aggregates with crystalline surface when viewed by Electron Microscopy. Circular dichroism spectra of P. semisulcatus β-GBP showed broad negative minimum wavelength extending from 200 to 250 nm can be attributed to the presence of β-sheets in its secondary structure. P. semisulcatus β-GBP comprises the specific binding affinity with the polysaccharide β-1, 3-glucans (laminarin), this recognition and binding leads to the activation of prophenoloxidase cascade. Interestingly, P. semisulcatus β-GBP also involved in the agglutination of baker's yeast, bacteria, erythrocytes (RBCs) and enhances the PO activity. Herein, we have investigated the importance of β-GBP in innate immune response of P. semisulcatus and they implicate the evolutionary link with similar proteins found in other invertebrates.

Effects of the water extract of Gynura bicolor (Roxb. & Willd.) DC on physiological and immune responses to Vibrio alginolyticus infection in white shrimp (Litopenaeus vannamei)

Gynura bicolor (Roxb. & Willd.) DC is widely distributed in certain areas of Asia and is very popular in vegetarian cuisine in Taiwan. To investigate the regulatory roles of G. bicolor in various functions in crustaceans, we examined innate non-specific immune responses (including total hemocyte count (THC), phenoloxidase activity (PO), respiratory bursts (RBs), and superoxide dismutase (SOD) activity), physiological responses (including haemolymph glucose, lactate, and lipids), and gene expressions (including prophenoloxidase (proPO), lipopolysaccharide- and b-1,3-glucan-binding protein (LGBP), and peroxinectin (PE) mRNA transcripts) to the pathogen Vibrio alginolyticus in white shrimp (Litopenaeus vannamei) that were individually injected with the water extract from G. bicolor at 2, 4, and 8 μg g(-1). Results indicated that PO, RBs, SOD activity, proPO, LGBP, and PE mRNA transcripts of shrimps receiving the water extract of G. bicolor at 2, 4, and 8 μg g(-1) significantly increased after challenge with V. alginolyticus for 96 h. However, no significant difference in the THC was seen at any dose. L. vannamei injected with the water extract of G. bicolor at all doses respectively maintained lower glucose, lactate, and lipid levels in response to V. alginolyticus challenge at 12-36, 24-36, and 24-48 h. Survival rates at 24-72 h of L. vannamei that received G. bicolor at any dose was significantly higher than those of shrimp that received saline. It was concluded that the water extract of G. bicolor can maintain physiological homeostasis and enhance immunity against V. alginolyticus infection in L. vannamei.

Prophenoloxidase system and its role in shrimp immune responses against major pathogens

The global shrimp industry still faces various serious disease-related problems that are mainly caused by pathogenic bacteria and viruses. Understanding the host defense mechanisms is likely to be beneficial in designing and implementing effective strategies to solve the current and future pathogen-related problems. Melanization, which is performed by phenoloxidase (PO) and controlled by the prophenoloxidase (proPO) activation cascade, plays an important role in the invertebrate immune system in allowing a rapid response to pathogen infection. The activation of the proPO system, by the specific recognition of microorganisms by pattern-recognition proteins (PRPs), triggers a serine proteinase cascade, eventually leading to the cleavage of the inactive proPO to the active PO that functions to produce the melanin and toxic reactive intermediates against invading pathogens. This review highlights the recent discoveries of the critical roles of the proPO system in the shrimp immune responses against major pathogens, and emphasizes the functional characterizations of four major groups of genes and proteins in the proPO cascade in penaeid shrimp, that is the PRPs, serine proteinases, proPO and inhibitors.

Pattern recognition receptors acting in innate immune system of shrimp against pathogen infections

Invertebrates, including shrimp, have developed very complicated innate immune system against pathogens. Much work has been performed on the innate immunity of shrimp, including immune recognition, signal transduction, effector molecules and antiviral responses due to its great economic value. Pattern recognition is the first step of innate immunity. Pattern recognition receptors (PRRs) sense the presence of infection and activate immune responses. The studies on shrimp PRRs revealed the recognition mechanism of shrimp at a certain degree. To date, 11 types of pattern recognition receptors (PRRs) have been identified in shrimp, namely, β-1,3-glucanase-related proteins, β-1,3-glucan-binding proteins, C-type lectins, scavenger receptors, galectins, fibrinogen-related proteins, thioester-containing protein, Down syndrome cell adhesion molecule, serine protease homologs, trans-activation response RNA-binding protein and Toll like receptors. A number of PRRs have been functionally studied and have been found to have different binding specificities and immune functions. The present review aims to summarize the current knowledge on the PRRs of shrimp.

A novel C-type lectin from crab Eriocheir sinensis functions as pattern recognition receptor enhancing cellular encapsulation

C-type lectins are a large family of Ca²⁺-dependent carbohydrate binding proteins which play crucial roles to recognize and eliminate pathogens in innate immunity. In the present study, a novel C-type lectin was identified from Eriocheir sinensis (designated as EsCTL). The full-length cDNA of EsCTL was of 789 bp with an open reading frame of 468 bp encoding a polypeptide of 156 amino acids with a signal sequence and single carbohydrate-recognition domain (CRD). The potential tertiary structure of the CRD adopted a typical double-loop structure with Ca²⁺-binding site 2 in the long loop region and two conserved disulfide bridges at the bases of the loops. An EPQ motif to determine carbohydrate binding specificity was identified in the CRD of EsCTL. The mRNA transcripts of EsCTL were mainly detected in hepatopancreas and its relative expression level in hemocytes was significantly up-regulated after the challenges of Vibrio anguillarum (P < 0.05) and Pichia pastoris (P < 0.05). The recombinant EsCTL protein (rEsCTL) could bind different PAMPs, including LPS, PGN, β-glucan, and polyI:C; and also bind various microorganisms including three Gram-positive bacteria, three Gram-negative bacteria and two yeasts. Moreover, rEsCTL could significantly enhance the in vitro encapsulation of crab hemocytes. All these results suggested that EsCTL functioned as an important PRR involved in immune defense against invading pathogen in crab.

Diversity and multiple functions of lectins in shrimp immunity

Lectins play important roles in many biological processes, including protein trafficking, cell signaling, pathogen recognition, as effector molecules, and so on, because of their capacity to bind carbohydrates. Presently, seven groups of lectins have been identified in shrimp: C-type, L-type, P-type, M-type, fibrinogen-like domain lectins, galectins, and calnexin/calreticulin. These lectins have different structures, diverse expression patterns, and multiple functions in the shrimp immune response. This review summarizes the research progress and analyzes the diversity of shrimp lectins, focusing mainly on the C-type lectin family. Shrimp C-type lectins show considerable diversity in their domain architectures, sugar substrates, tissue distributions, expression patterns responding to pathogen challenge and functions in shrimp immunity.

Particularity and universality of a putative Gram-negative bacteria-binding protein (GNBP) gene from amphioxus (Branchiostoma belcheri): insights into the function and evolution of GNBP

Gram-negative bacteria-binding proteins (GNBPs) are important pattern recognition proteins (PRPs), which can initiate host defense in response to pathogen surface molecules. The roles of GNBP in innate immunity of arthropods and molluscs have recently been reported. However, the GNBP gene has not been characterized in the species of higher evolutionary status yet. In this study, we identified and characterized an amphioxus GNBP gene (designated as AmphiGNBP). First, we identified and cloned the AmphiGNBP and found that the AmphiGNBP encodes a putative protein with 558 amino acids, which contains a conserved β-1, 3-glucan recognizing and binding domain. Second, we found that the AmphiGNBP encodes two extra WSC (cell Wall integrity and Stress response Component) domains, which are unique in AmphiGNBP protein. The two WSC domains of AmphiGNBP protein coupled with the expansion of amphioxus immunity repertoire might undergo intensive domain shuffling during the age of the Cambrian explosion. Finally, we found that the AmphiGNBP was mainly expressed in immune tissues, such as hepatic cecum and intestine, and the expression of AmphiGNBP was affected after LPS stimulation. In conclusion, our findings disclose the particularity and universality of AmphiGNBP and provide profound insights into the function and evolution of GNBP.

Molecular cloning of prophenoloxidase and the effects of dietary β-glucan and rutin on immune response in hemocytes of the fleshy shrimp, Fenneropenaeus chinensis

To investigate the effects of dietary β-glucan (0.5 or 1 g kg⁻¹ diet: 0.5-BG, 1-BG) and rutin (0.5 or 1 g kg⁻¹ diet: 0.5-RT, 1-RT) after 10 days in the absence of pathogen challenge on the immune response of Fenneropenaeus chinensis, we determined total hemocyte count (THC) and the expression of four immune-related genes in hemocytes: those for prophenoloxidase (proPO), peroxinectin (PX), lipopolysaccharide and/or β-glucan binding protein (LGBP), and c-type lectin (CL). As a prerequisite for subsequent experiments, cDNA encoding proPO of the fleshy shrimp, Fenneropenaeus chinensis (f-proPO) was obtained from hemocytes; it had a full length of 3023 bp, with an open reading frame (ORF) of 2061bp, a 105-bp 5'-untranslated region, and a 906-bp 3'-untranslated region containing the poly A signal. The THCs of shrimp fed β-glucan of 1 g kg⁻¹ diet, and rutin of 1 g kg⁻¹ diet were significantly higher than that of the control (P < 0.05). The expression of proPO mRNA was slightly downregulated and that of LGBP mRNA was upregulated (except in 1-RT). PX and CL mRNA remained constitutively expressed in all groups. Our results reveal that β-glucan and rutin dietary supplements have minimal effect on immune response in the absence of pathogen challenge.

The effect of fucoidan from brown seaweed Sargassum wightii on WSSV resistance and immune activity in shrimp Penaeus monodon (Fab)

The polysaccharide-fucoidan was extracted from brown seaweed Sargassum wightii and characterized through FT-IR and (13)C &(1)H NMR analysis. The extracted fucoidan was supplemented with pellet diets at three different concentrations (0.1, 0.2 and 0.3%). The fucoidan supplemented diets were fed to Penaeus monodon for 45 days, then challenged with WSSV and the mortality percentage was recorded daily up to 21 days. During the challenge test, the control group showed 100% mortality within 10 days, but in the experimental groups, the mortality percentage (51-72% within 21 days) was decreased considerably (P < 0.05) with respect to the concentrations of fucoidan. The reduction in mortality percentage of experimental groups over control group was ranged from 50.81 to 68.06%. During challenge experiment, the immunological parameters such as THC, prophenoloxidase activity, respiratory burst activity, superoxide dismutase activity and phagocytic activity were measured before injection of WSSV (0 day) and after the injection of WSSV on 10th and 21st days, respectively. All the immunological parameters of experimental groups were significantly (P < 0.05) increased than control group. RT-PCR analysis confirmed the considerable reduction of WSSV DNA copy numbers with respect to the concentration of fucoidan. It was concluded that P. monodon fed with fucoidan of S. wightii supplemented diet had enhanced the innate immunity and increased resistance against WSSV infection.

Pattern recognition protein binds to lipopolysaccharide and β-1,3-glucan and activates shrimp prophenoloxidase system

The prophenoloxidase (proPO) system is activated upon recognition of pathogens by pattern recognition proteins (PRPs), including a lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP). However, shrimp LGBPs that are involved in the proPO system have yet to be clarified. Here, we focus on characterizing the role of a Penaeus monodon LGBP (PmLGBP) in the proPO system. We found that PmLGBP transcripts are expressed primarily in the hemocytes and are increased at 24 h after pathogenic bacterium Vibrio harveyi challenge. The binding studies carried out using ELISA indicated that recombinant (r)PmLGBP binds to β-1,3-glucan and LPS with a dissociation constant of 6.86 × 10(-7) M and 3.55 × 10(-7) M, respectively. Furthermore, we found that rPmLGBP could enhance the phenoloxidase (PO) activity of hemocyte suspensions in the presence of LPS or β-1,3-glucan. Using dsRNA interference-mediated gene silencing assay, we further demonstrated that knockdown of PmLGBP in shrimp in vivo significantly decreased the PmLGBP transcript level but had no effect on the expression of the other immune genes tested, including shrimp antimicrobial peptides (AMPs). However, suppression of proPO expression down-regulated PmLGBP, proPO-activating enzyme (PmPPAE2), and AMPs (penaeidin and crustin). Such PmLGBP down-regulated shrimp showed significantly decreased total PO activity. We conclude that PmLGBP functions as a pattern recognition protein for LPS and β-1,3-glucan in the shrimp proPO activating system.

Dietary administration of a Gracilaria tenuistipitata extract enhances the immune response and resistance against Vibrio alginolyticus and white spot syndrome virus in the white shrimp Litopenaeus vannamei

The haemogram, phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, lysozyme activity, and the mitotic index of haematopoietic tissue (HPT) were examined after the white shrimp Litopenaeus vannamei had been fed diets containing the hot-water extract of Gracilaria tenuistipitata at 0 (control), 0.5, 1.0, and 2.0 g kg(-1) for 7-35 days. Results indicated that these parameters directly increased with the amount of extract and time, but slightly decreased after 35 days. RBs, SOD activity, and GPx activity reached the highest levels after 14 days, whereas PO and lysozyme activities reached the highest levels after 28 days. In a separate experiment, white shrimp L. vannamei, which had been fed diets containing the extract for 14 days, were challenged with Vibrio alginolyticus at 2 × 10(6) cfu shrimp(-1) and white spot syndrome virus (WSSV) at 1 × 10(3) copies shrimp(-1), and then placed in seawater. The survival rate of shrimp fed the extract-containing diets was significantly higher than that of shrimp fed the control diet at 72-144 h post-challenge. We concluded that dietary administration of the G. tenuistipitata extract at ≤1.0 g kg(-1) could enhance the innate immunity within 14 days as evidenced by the increases in immune parameters and mitotic index of HPT in shrimp and their enhanced resistance against V. alginolyticus and WSSV infections. Shrimp fed the extract-containing diets showed a higher and continuous increase in the humoral response indicating its persistent role in innate immunity.

White shrimp Litopenaeus vannamei immersed in seawater containing Sargassum hemiphyllum var. chinense powder and its extract showed increased immunity and resistance against Vibrio alginolyticus and white spot syndrome virus

This study was to examine the immune response of white shrimp Litopenaeus vannamei and its resistance against Vibrio alginolyticus and WSSV when shrimp received the Sargassum hemiphyllum var. chinense powder and its hot-water extract. Both powder and extract showed activation of prophenoloxidase and generation of superoxide anion in the shrimp in vitro. The haemocyte count, phenoloxidase (PO) activity, respiratory burst, and lysozyme activity were examined after the shrimp were immersed in seawater containing S. hemiphyllum var. chinense powder or its extract at 0, 100, 300, and 500 mg L⁻¹ for 1, 3, and 5 h. These immune parameters of shrimp immersed in 300 and 500 mg L⁻¹ powder, and 100 and 300 mg L⁻¹ extract were significantly higher than those of control shrimp after 3 h, but slightly decreased after 5 h. In another experiment, shrimp immersed in seawater containing the powder or the extract at 0, 100, 300, and 500 mg L⁻¹ after 3 h were challenged with V. alginolyticus at 8 × 10⁵ colony-forming unit (cfu) shrimp⁻¹, or challenged with WSSV at 1 × 10⁵ copies shrimp⁻¹, and then placed in seawater. Survival rate of shrimp immersed in 500 mg L⁻¹ powder was significantly higher than that of control shrimp after 24-120 h in the V. alginolyticus-challenge test, and after 72 h in the WSSV-challenge test, respectively. Survival rate of shrimp immersed in 300 mg L⁻¹ extract was significantly higher than that of control shrimp after 72-120 h in both V. alginolyticus-challenge and WSSV-challenge tests. It was concluded that the shrimp immersed in seawater containing the powder at 500 mg L⁻¹, and the extract at 300 mg L⁻¹ had increased immunity and resistance against V. alginolyticus infection, and the shrimp that received extract at 300 mg L⁻¹ showed resistance against WSSV infection.

Recognition of microbial molecular patterns and stimulation of prophenoloxidase activation by a β-1,3-glucanase-related protein in Manduca sexta larval plasma

Detection of pathogenic invaders is the essential first step of a successful defense response in multicellular organisms. In this study, we have identified a new member of the β-1,3-glucanase-related protein superfamily from the tobacco hornworm Manduca sexta. This protein, designated microbe binding protein (MBP), is 61% identical in sequence to Bombyx mori Gram-negative bacteria binding protein, but only 34-36% identical to M. sexta β-1,3-glucan recognition protein-1 and 2. Its mRNA levels were strongly up-regulated in hemocytes and fat body of immune challenged larvae, along with an increase in concentration of the plasma protein. We expressed M. sexta MBP in a baculovirus-insect cell system. The purified protein associated with intact bacteria and fungi. It specifically bound to lipoteichoic acid, lipopolysaccharide, diaminopimelic acid-type peptidoglycans (DAP-PGs) from Escherichia coli and Bacillus subtilis, but less so to laminarin or Lys-type PG from Staphylococcus aureus. The complex binding pattern was influenced by other plasma factors and additional microbial surface molecules. After different amounts of MBP had been incubated with larval plasma on ice, a concentration-dependent increase in phenoloxidase (PO) activity occurred in the absence of any microbial elicitor. The activity increase was also observed in the mixture of plasma and a bacterial or fungal cell wall component. The prophenoloxidase (proPO) activation became more prominent when DAP-PGs, Micrococcus luteus Lys-PG, or lipoteichoic acid was included in the mixture of MBP and plasma. Statistic analysis suggested that a synergistic enhancement of proPO activation was caused by an interaction between MBP and these elicitors, but not S. aureus Lys-PG, lipopolysaccharide, curdlan, or laminarin. These data indicate that M. sexta MBP is a component of the surveillance mechanism and, by working together with other pattern recognition molecules and serine proteinases, triggers the proPO activation system.

Cloning and characterization of a shrimp ML superfamily protein

ML superfamily proteins, including MD-1, MD-2, Niemann-Pick type C2 (Npc2) protein, GM2 activator protein, phosphatidylinositol/phosphatidylglycerol transfer protein (PG/PI-TP) and mite allergen Der p 2, bind to specific lipids and play important roles in lipid-recognition and metabolism. Among these ML (MD-2-related lipid-recognition) proteins, MD-2 is essential for lipopolysaccharide (LPS) signaling and the following secretion of proinflammatory factors. In this report, we identified the cDNA and gene of an ML protein from an important white shrimp Litopenaeus vannamei and named it LvML. The gene consists of four exons and three introns. The putative LvML contains 6 cysteines which may form 3 disulfide bonds that are conserved in ML proteins. Reverse transcription PCR analysis showed that in the examined tissues LvML mRNA is only expressed in the hepatopancreas, while not in hemocytes, eyestalk, gill, heart, stomach, intestine, nerve core, muscle or pyloric caecum. Its expression is positively regulated after injection of LPS. Then enzyme-linked immunosorbent assay showed that the recombinant LvML possessed activity of binding to LPS, and that the binding was inhibited by pre-incubation with LPS. We suggested that the LvML may play roles in the shrimp innate immunity.

Identification and characterization of multiple beta-glucan binding proteins in the Pacific oyster, Crassostrea gigas

The present study reports on the characterization of two cDNAs coding beta-glucan binding proteins (betaGBPs), designated as Cg-betaGBP-1 and Cg-betaGBP-2, from the Pacific oyster, Crassostrea gigas. Cg-betaGBP-1 consists of 555 amino acid residues and possesses two possible integrin recognition sites. The other protein, Cg-betaGBP-2, is composed of 447 amino acid residues without integrin recognition sites. Domain structures of both Cg-betaGBPs are similar to other invertebrate betaGBPs, but phylogenetic positions and major expression tissues for these proteins are different. Cg-betaGBP-1 is expressed in circulatory hemocytes and Cg-betaGBP-2 in digestive glands. Functional assays using recombinant proteins revealed that Cg-betaGBP-2 enhanced the phenoloxidase (PO) activity of hemocyte suspensions under the presence of laminarin, but Cg-betaGBP-1 did not show this enhancement. It is suggested that Cg-betaGBPs in the Pacific oyster have evolved to obtain different immunological functions. Cg-betaGBP-1 possibly evolved for hemocyte-related functions through integrin, and Cg-betaGBP-2 for the PO activation system.

Molecular cloning and characterization of lipopolysaccharide- and beta-1,3-glucan-binding protein from the giant freshwater prawn Macrobrachium rosenbergii and its transcription in relation to foreign material injection and the molt stage

Lipopolysaccharide (LPS)- and beta-1,3-glucan-binding protein (LGBP) complementary (c)DNA was cloned from the hepatopancreas of the giant freshwater prawn Macrobrachium rosenbergii using oligonucleotide primers and a reverse-transcription polymerase chain reaction (RT-PCR). Both 3'- and 5'-regions were isolated by the rapid amplification of cDNA ends (RACE) method. Analysis of the nucleotide sequence revealed that the cDNA clone has an open reading frame of 1389 bp encoding a protein of 378 amino acids (aa) including a 15-aa signal peptide. The calculated molecular mass of the mature protein (363 aa) was 41.2 kDa with an estimated pI of 4.73. The M. rosenbergii LGBP sequence contains (1) three putative integrin-binding motifs, (2) a glucanase motif, (3) a putative N-glycosylation site, (4) four protein kinase C phosphorylation sites, (5) four casein kinase II phosphorylation sites, and (6) a putative recognition motif. Sequence comparison showed that the deduced amino acids of LGBP of M. rosenbergii had overall similarities of 60-71% to those of known crustacean LGBPs and beta-1,3-glucan-binding proteins (BGBPs). The LGBP of M. rosenbergii was mainly expressed in the hepatopancreas. The LGBP transcript of M. rosenbergii was downregulated in haemocytes, but was upregulated in the hepatopancreas when injected with LPS and poly:IC after 12 h. The LGBP messenger (m)RNA expression of prawns in the postmolt stage was significantly upregulated in haemocytes, but downregulated in the hepatopancreas, which revealed a complementary relationship between haemocytes and the hepatopancreas in the molt cycle.