Two C-type lectins from shrimp Litopenaeus vannamei that might be involved in immune response against bacteria and virus

PvMR1, a novel C-type lectin plays a crucial role in the antibacterial immune response of Pacific white shrimp, Penaeus vannamei

C-type lectins (CTLs) are important immune molecules in innate immune, which participate in non-self recognition and clearance of pathogens. Here, a new CTL with two distinct C-type lectin domains (CTLDs) from Pacific white shrimp Penaeus vannamei, designated as PvMR1 was identified. The obtained PvMR1 coding sequence (CDS) was 1044 bp long encoding a protein with 347 amino acids. PvMR1 had two CTLD, a conserved mannose-specific EPN motif and a galactose-specific QPD motif, clustering into the same branch as the crustacean CTLs. PvMR1 was widely distributed in shrimp tissues with the highest transcription level in the hepatopancreas, with significantly induced mRNA expression on the hepatopancreas and intestines after immune challenge with Vibrio anguillarum. In vitro assays with recombinant PvMR1 (rPvMR1) protein revealed that it exhibited a wide range of antimicrobial activity, bacterial binding ability, and bacterial agglutination activity in a Ca2+-independent manner. Moreover, PvMR1 promoted bacterial phagocytosis in hemocytes. Furthermore, rPvMR1 treatment could significantly enhance the bacterial clearance in hemolymph and greatly improved the survival of shrimp under V. anguillarum infection in vivo. These results collectively suggest that PvMR1 plays an important role in antibacterial immune response of P. vannamei.

Structural and functional diversity of lectins associated with immunity in the marine shrimp Litopenaeusvannamei

Lectins are important pattern recognition receptors (PRRs) and their immunological action is related to the recognition of glycans present in the pathogen cells surface. The lectins described for Litopenaeus vannamei are divided into C-type, L-type and galectin, which are mainly expressed in hepatopancreas and hemocytes. They are involved in several immune response pathways, such as phagocytosis, hemocytes recruitment, prophenoloxidase activation, and gene regulation. Although lectins have multiple immune functions, most experimental challenges focus only on WSSV and Vibrio sp. This article is a detailed review on the role of lectins in L. vannamei immune system, bringing together information on molecular structure, temporal and special expression and immune function, highlighting the wide participation of these molecules in shrimp innate immune system.

A Novel Disease (Water Bubble Disease) of the Giant Freshwater Prawn Macrobrachium rosenbergii Caused by Citrobacter freundii: Antibiotic Treatment and Effects on the Antioxidant Enzyme Activity and Immune Responses

The giant freshwater prawn, Macrobrachium rosenbergii, is an important and economical aquaculture species widely farmed in tropical and subtropical areas of the world. A new disease, “water bubble disease (WBD)”, has emerged and resulted in a large loss of M. rosenbergii cultured in China. A water bubble with a diameter of about 7 mm under the carapace represents the main clinical sign of diseased prawns. In the present study, Citrobacter freundii was isolated and identified from the water bubble. The optimum temperature, pH, and salinity of the C. freundii were 32 °C, 6, and 1%, respectively. A challenging experiment showed that C. freundii caused the same typical signs of WBD in prawns. Median lethal dose of the C. freundii to prawn was 104.94 CFU/g. According to the antibiogram tests of C. freundii, florfenicol and ofloxacin were selected to evaluate their therapeutic effects against C. freundii in prawn. After the challenge with C. freundii, 86.67% and 72.22% survival of protective effects against C. freundii were evaluated in the oral florfenicol pellets and oral ofloxacin pellets feding prawns, respectively, whereas the mortality of prawns without fed antibiotics was 93%. After antibiotic treatment and C. freundii infection, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), malondialdehyde (MDA), acid phosphatase (ACP), alkaline phosphatase (ALP), and lysozyme (LZM) in the hemolymph and hepatopancreas of the prawns and the immune-related gene expression levels of Cu/Zn-SOD, CAT, GPx, GST, LZM, ACP, anti-lipopolysaccharide factor, crustin, cyclophilin A, and C-type lectin in hepatopancreas were all significantly changed, indicating that innate immune responses were induced by C. freundii. These results can be beneficial for the prevention and control of C. freundii in prawns.

Molecular cloning, sequence characterization, and expression analysis of C-type lectin (CTL) and ER-Golgi intermediate compartment 53-kDa protein (ERGIC-53) homologs from the freshwater prawn, Macrobrachium rosenbergii

Lectin protein families are diverse and multi-functional in crustaceans. The carbohydrate-binding domains (CRDs) of lectins recognize the molecular patterns associated with pathogens and orchestrate important roles in crustacean defense. In this study, two lectin homologs, a single CRD containing C-type lectin (CTL) and an L-type lectin (LTL) domain containing endoplasmic reticulum Golgi intermediate compartment 53 kDa protein (ERGIC-53) were identified from the freshwater prawn, Macrobrachium rosenbergii. The open reading frames of MrCTL and MrERGIC-53 were 654 and 1,515 bp, encoding polypeptides of 217 and 504 amino acids, respectively. Further, MrCTL showed a 20-amino acid transmembrane helix region and 10 carbohydrate-binding residues within the CRD. MrERGIC-53 showed a signal peptide region, a type-I transmembrane region, and a coiled-coil region at the C-terminus. Phylogenetic analysis revealed a close relationship between MrCTL and MrLectin and M. nipponense CTL (MnCTL), whereas MrERGIC-53 shared high sequence identity with Eriocheir sinensis ERGIC-53 and Penaeus vannamei MBL-1. A homology-based model predicted small carbohydrate-combining sites with a metal-binding site for ligand binding (Ca²⁺ binding site) in MrCTL and beta-sheets connected by short loops and beta-bends forming a dome-shaped beta-barrel structure representing the LTL domain of MrERGIC-53. Quantitative real-time polymerase chain reaction detected MrCTL and MrERGIC-53 transcripts in all examined tissues, with particularly high levels observed in hemocytes, hepatopancreas, and mucosal-associated tissues, such as the stomach and intestine. Further, the expression levels of MrCTL and MrERGIC-53 transcripts were remarkably altered after V. harveyi challenge, suggesting putative function in host innate immunity.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10499-022-00845-3.

A novel C-type lectin LvCTL 4.2 has antibacterial activity but facilitates WSSV infection in shrimp (L. vannamei)

Glycan-binding protein C-type lectin (CTL), one of the pattern recognition receptors (PRRs), binds to carbohydrates on the surface of pathogens and elicits antimicrobial responses in shrimp innate immunity. The objective was to identify and characterize a novel C-type lectin LvCTL 4.2 in Litopenaeus vannamei. The LvCTL 4.2 protein consisted of a signal peptide at the N terminal and a carbohydrate-recognition domain (CRD) with a mutated mannose-binding (Glu-Pro-Ala; EPA) motif at the C terminal, and thereby has a putative secreted mannose-binding C-type lectin architecture. LvCTL 4.2 was highly expressed in nervous tissue and stomach. Infection with white spot syndrome virus (WSSV) induced expression of LvCTL 4.2 in shrimp stomach at 12 h post infection. Conversely, there was no obvious upregulation in expression of LvCTL 4.2 in stomach or hepatopancreas of shrimp with AHPND (acute hepatopancreas necrosis disease). Pathogen binding assays confirmed recombinant LvCTL 4.2 protein (rLvCTL 4.2) had significant binding ability with the WSSV virion, Gram-negative, and Gram-positive bacteria. Moreover, rLvCTL 4.2 had strong growth inhibition of Vibrio parahaemolyticus. Silencing LvCTL 4.2 suppressed WSSV replication, whereas pretreatment of WSSV with rLvCTL 4.2 facilitated viral replication in vivo. In conclusion, LvCTL 4.2 acted as a PRR that inhibited AHPND-causing bacteria, but facilitated WSSV pathogenesis.

Population Structure, Genetic Connectivity, and Signatures of Local Adaptation of the Giant Black Tiger Shrimp (Penaeus monodon) throughout the Indo-Pacific Region

The giant black tiger shrimp (Penaeus monodon) is native to the Indo-Pacific and is the second most farmed penaeid shrimp species globally. Understanding genetic structure, connectivity, and local adaptation among Indo-Pacific black tiger shrimp populations is important for informing sustainable fisheries management and aquaculture breeding programs. Population genetic and outlier detection analyses were undertaken using 10,593 genome-wide single nucleotide polymorphisms (SNPs) from 16 geographically disparate Indo-Pacific P. monodon populations. Levels of genetic diversity were highest for Southeast Asian populations and were lowest for Western Indian Ocean (WIO) populations. Both neutral (n = 9,930) and outlier (n = 663) loci datasets revealed a pattern of strong genetic structure of P. monodon corresponding with broad geographical regions and clear genetic breaks among samples within regions. Neutral loci revealed seven genetic clusters and the separation of Fiji and WIO clusters from all other clusters, whereas outlier loci revealed six genetic clusters and high genetic differentiation among populations. The neutral loci dataset estimated five migration events that indicated migration to Southeast Asia from the WIO, with partial connectivity to populations in both oceans. We also identified 26 putatively adaptive SNPs that exhibited significant Pearson correlation (P < 0.05) between minor allele frequency and maximum or minimum sea surface temperature. Matched transcriptome contig annotations suggest putatively adaptive SNPs involvement in cellular and metabolic processes, pigmentation, immune response, and currently unknown functions. This study provides novel genome-level insights that have direct implications for P. monodon aquaculture and fishery management practices.

A typical C-type lectin, perlucin-like protein, is involved in the innate immune defense of whiteleg shrimp Litopenaeus vannamei

C-type lectins are a large group of the pattern-recognition proteins, and have been reported to be involved in invertebrate innate immunity, such as cell adhesion, bacterial clearance, phagocytosis, prophenoloxidase activation and encapsulation. Here, a perlucin-like protein (PLP), a typical C-type lectin, was identified from the cDNA library of the shrimp, Litopenaeus vannamei. LvPLP contains a 540 bp open reading frame, encoding a protein of 179 amino acids that includes a single carbohydrate-recognition domain. Phylogenetic analysis showed that LvPLP was clustered into a single group together with other perlucins from molluscs. Quantitative real-time PCR revealed that LvPLP was expressed mainly in the hemocytes, hemolymph, heart and gills. The transcription of LvPLP was significantly induced at 9 h by both Gram^- bacteria Vibrio parahaemolyticus and Vibrio anguillarum. Meanwhile, recombinant LvPLP (rLvPLP) bound directly to lipopolysaccharide and peptidoglycan with different affinity. rLvPLP showed a strong ability to bind to Gram⁺ (Staphylococcus aureus and Bacillus subtilis) and Gram^- bacteria (V. parahaemolyticus and V. anguillarum), and could induce agglutination of V. parahaemolyticus and V. anguillarum, but not S. aureus and B. subtilis in the presence Ca²⁺. Further study showed that when LvPLP was knocked down by RNAi, three phagocytosis-related genes (peroxinectin, mas-like protein and dynamin) and four antimicrobial peptide (AMP) genes (crustin, ALF1, ALF2 and ALF3) were significantly decreased. Altogether, these results demonstrated that LvPLP played a vital role in L. vannamei immune response towards bacterial challenge by binding and agglutinating bacteria and influencing phagocytosis and AMP expression.

Comparative proteomic investigation of Marsupenaeus japonicus hepatopancreas challenged with Vibrio parahaemolyticus and white spot syndrome virus

This study aimed to use isobaric tags (IBTs) to investigate the immune response of the hepatopancreas of Marsupenaeus japonicas infected with Vibrio parahaemolyticus or white spot syndrome virus (WSSV). Liquid chromatography-tandem mass spectrometry and protein sequencing identified 1005 proteins. Among them, 109 proteins were upregulated and 94 were downregulated after V. parahaemolyticus infection. After WSSV infection, 130 proteins were identified as differentially abundant, including 88 that were upregulated and 42 were downregulated. Fifty-four proteins were identified as differentially abundant after both V. parahaemolyticus and WSSV infection. A number of proteins related to cytoskeletal processes, including actin and myosin, and apoptosis-related proteins were upregulated in shrimp after V. parahaemolyticus and WSSV infection, indicating that phagocytosis and apoptosis may be involved in the response to in V. parahaemolyticus or WSSV infection. Quantitative real-time PCR was carried out to verify the reliability of the proteomic data. These data provide a basis to characterize the immunity-related processes of shrimp in response to infection with WSSV or V. parahaemolyticus.

Molecular cloning, characterization, and expression of a C-type lectin from Scylla paramamosain, which might be involved in the innate immune response

C-type lectins (CTLs) have characteristic carbohydrate recognition domains (CRDs) and play important roles in the immune system. In the present study, a new CTL, SpCTL5, was identified from the hepatopancreas of the mud crab Scylla paramamosain. The open reading frame of SpCTL5 comprised 762 bp, encoding a polypeptide of 253 amino acids with a putative signaling peptide of 20 amino acids. The predicted SpCTL5 protein contained a single CRD. SpCTL5 transcripts were distributed in all examined tissues, with the highest level being detected in the hepatopancreas. Upon challenging with Vibrio alginolyticus, the mRNA levels of SpCTL5 in the hepatopancreas were up-regulated. The recombinant protein of SpCTL5 could agglutinate three Gram-positive bacteria and three Gram-negative bacteria in the presence of Ca²⁺. Furthermore, hemagglutination analysis showed that the recombinant protein of SpCTL5 can agglutinate rabbit erythrocytes. This study indicated that SpCTL5 acts as a pattern recognition receptor for the innate immune response which protects S. paramamosain from bacterial infection. Moreover, these findings also provide information to further our understanding of the innate immunology of invertebrates.

Exposure to Aeromonas hydrophila induces inflammation and increases expression of the gene encoding for a putative dual CTLD-containing lectin in milkfish liver

Milkfish (Chanos chanos Forsskal) is an important aquaculture product and is the sole extant species of the family Chanidae (order Gonorynchiformes). While there are already several reports regarding milkfish aquaculture, studies on milkfish immunity and gene expression are very limited. In this study, we showed that Aeromonas hydrophila induces inflammation in milkfish liver. We identified a milkfish C-type lectin-like domain containing proteins (CTLDcps) gene, designated as CcClec, which was upregulated in respond to A. hydrophila. Full-length sequencing was performed using Rapid Amplification of cDNA Ends (RACE PCR) to produce a complete Coding DNA Sequence (CDS) of the gene. The CcClec gene encoded a predicted protein of 340 amino acids containing two CTLDs that may potentially bind carbohydrates, especially sucrose and cellobiose. The CcClec mRNA transcript was expressed highest in the liver, followed by head kidney, brain, heart, gills, spleen, and midgut. CcClec transcripts were upregulated in damaged liver upon exposure to A. hydrophila. Overall, these findings demonstrated that CcClec is implicated in milkfish innate immunity, and is most highly expressed in the liver, suggesting a role of the liver in the milkfish immune system.

Identification and characterization of a novel PRR of fibrinogen-related protein in Apostichopus japonicus

Fibrinogen-related proteins (FREPs) play important roles in innate immunity by recognizing pathogen associated molecular patterns on pathogenic bacteria surfaces via conserved fibrinogen-like domain (FBG). In this paper, the full-length cDNA of Apostichopus japonicus FREP (designated as AjFREP) was cloned combined with rapid amplification of cDNA ends (RACE) and transcriptome sequencing. The full-length cDNA of AjFREP was of 2110 bp with an open reading frame (ORF) of 1659 bp. SMART analysis revealed that the AjFREP contained a typical signal peptide of 19 amino acid residues, a FBG and two unusual epidermal growth factor-like domains (EGFs). Multiple sequence alignments suggested that FBG domain shared a remarkably high structural conservation in polypeptide binding site and Ca²⁺ binding site. Tissue distribution analysis revealed that AjFREP was constitutively expressed in all examined tissues with the largest magnitude in coelomocytes, indicating AjFREP might play an important role in immune defense. The mRNA level of AjFREP in coelomocytes was sharply up-regulated by Vibrio splendidus challenge, and reached its peak expression at 48 h. Knock-down AjFREP by specific siRNA could significantly repress the coelomocyte phagocytosis rate. Meantime, the survival number of V. splendidus in the coelomic fluid was promoted. All these current results indicated that AjFREP might be involved in pathogen clearance through mediating coelomocytes phagocytosis activity.

C-type lectin B (SpCTL-B) regulates the expression of antimicrobial peptides and promotes phagocytosis in mud crab Scylla paramamosain

As pattern recognition receptors, C-type lectins (CTLs) play important roles in immune system of crustaceans through identifying and binding to the conservative pathogen-associated molecular patterns (PAMPs) on pathogen surfaces. In this study, a new CTL, SpCTL-B, was identified from the hemocytes of mud crab Scylla paramamosain. The full-length of SpCTL-B cDNA was 1278 bp with an open reading frame (ORF) of 348 bp. The predicted SpCTL-B protein contains a single carbohydrate-recognition domain (CRD). SpCTL-B transcripts were distributed in all examined tissues with the highest levels in hepatopancreas. After challenged with Vibrio parahaemolyticus, LPS, polyI:C and white spot syndrome virus (WSSV), the mRNA levels of SpCTL-B in hemocytes and hepatopancreas were up-regulated. The recombinant SpCTL-B (rSpCTL-B) purified by Ni-affinity chromatography showed stronger binding activities with Staphylococcus aureus, β-hemolytic Streptococcus, Escherichia coli, Aeromonas hydrophila, Vibrio alginolyticus than those with V. parahaemolyticus and Saccharomyces cerevisiae. rSpCTL-B exhibited a broad spectrum of microorganism-agglutination activities against Gram-positive bacteria (S. aureus, β-hemolytic Streptococcus) and Gram-negative bacteria (E. coli, V. parahaemolyticus, A. hydrophila, V. alginolyticus) in a Ca²⁺-dependent manner. The agglutination activities of rSpCTL-B could be inhibited by D-mannose and LPS, but not by d-fructose and galactose. The antimicrobial assay showed that rSpCTL-B exhibited the growth inhibition against all examined gram-positive bacteria and gram-negative bacteria. When SpCTL-B was silenced by RNAi, the bacterial clearance ability in mud crab was decreased and the transcript levels of five antimicrobial peptides (AMPs) (SpCrustin, SpHistin, SpALF4 (anti-lipopolysaccharide factor), SpALF5 and SpALF6) were significantly decreased in hemocytes. In our study, knockdown of SpCTL-B could down-regulate the expression of SpSTAT at mRNA transcriptional level and protein translational level in mud crab. Meantime, the phagocytosis rate and the expression of three phagocytosis related genes were declined after RNAi of SpCTL-B in hemocytes in mud crab. Collectively, our results suggest that SpCTL-B might play its roles as a pattern recognition receptor (PRR) in immune response towards pathogens infection through influencing the expression of AMPs and the phagocytosis of hemocytes in mud crab S. paramamosain.

The functional characterization and comparison of two single CRD containing C-type lectins with novel and typical key motifs from Portunus trituberculatus

C-type lectins are a superfamily of Ca²⁺-dependent carbohydrate-recognition proteins, which play crucial roles in innate immunity including nonself-recognition and pathogen elimination. In the present study, two single-CRD containing C-type lectins were identified from swimming crab Portunus trituberculatus (designated as PtCTL-2 and PtCTL-3). The open reading frame (ORF) of PtCTL-2 encoded polypeptides of 485 amino acids with a signal peptide and a single carbohydrate-recognition domain (CRD), while PtCTL-3's ORF encoded polypeptides of 241 amino acids with a coiled-coil region and a single-CRD. The key motifs determining carbohydrate binding specificity in PtCTL-2 and PtCTL-3 were EPR (Glu-Pro-Arg) and QPD (Gln-Pro-Asp). EPR is a motif being identified for the first time, whereas QPD is a typical motif in C-type lectins. Different PAMPs binding features of the two recombinant proteins - PtCTL-2 (rPtCTL-2) and PtCTL-3 (rPtCTL-3) have been observed in our experiments. rPtCTL-2 could bind three pathogen-associated molecular patterns (PAMPs) with relatively high affinity, including glucan, lipopolysaccharide (LPS) and peptidoglycan (PGN), while rPtCTL-3 could barely bind any of them. However, rPtCTL-2 could bind seven kinds of microbes and rPtCTL-3 could bind six kinds in microbe binding assay. Moreover, rPtCTL-2 and rPtCTL-3 exhibited similar agglutination activity against Gram-positive bacteria, Gram-negative bacteria and fungi in agglutination assay. All these results illustrated that PtCTL-2 and PtCTL-3 could function as important pattern-recognition receptors (PRR) with broad nonself-recognition spectrum involved in immune defense against invaders. In addition, the results of carbohydrate binding specificity showed that PtCTL-2 with novel key motif had broad carbohydrate binding specificity, while PtCTL-3 with typical key motif possessed different carbohydrate binding specificity from the classical binding rule. Furthermore, PtCTL-2 and PtCTL-3 could also function as opsonin to enhance encapsulation of hemocytes against Ni-NTA beads.

A mannose-specific C-type lectin from Fenneropenaeus merguiensis exhibited antimicrobial activity to mediate shrimp innate immunity

Being one type of pattern recognition receptors (PRRs), lectins exhibit a crucial role in the defense mechanism of invertebrates which are deficient in an adaptive immune system. A new C-type lectin called FmLC3 was isolated from hepatopancreas of Fenneropenaeus merguiensis by cloning approaches, RT-PCR and 5' and 3' RACE (rapid amplification of cDNA ends). A full-length cDNA of FmLC3 contains 607 bp with one open reading frame of 480bp, encoding a 159-amino acids peptide. The predicted primary structure of FmLC3 is composed of a signal peptide, a carbohydrate recognition domain with an EPN motif and one Ca²⁺ binding site-2, including a double-loop region assisted by two conserved disulfide linkages. FmLC3 had a molecular mass of 17.96kDa and pI of 4.92. In normal or unchallenged shrimp, the mRNA expression of FmLC3 was detected only in hepatopancreas whilst its native proteins were found in hemolymph, heart, stomach and intestine but not in the expressed tissue, indicating that after being synthesized in hepatopancreas, FmLC3 would be secreted to other tissues. The significant up-regulation of FmLC3 was manifested in shrimp challenged with Vibrio harveyi or white spot syndrome virus. After knockdown with gene-specific double-stranded RNA and following by co-pathogenic inoculation, the FmLC3 expression was severely suppressed with coherence of increasing in cumulative mortality and reduction of the median lethal time. Recombinant FmLC3 (rFmLC3) had agglutinating activity towards diverse bacterial strains in a Ca²⁺-dependent manner. Its activity was inhibited by lipopolysaccharide and mannose, implying that FmLC3 was mannose-binding C-type lectin. Moreover, rFmLC3 could bind directly to various microbial strains with Ca²⁺-requirement. Otherwise, rFmLC3 exhibited the antimicrobial activity by inhibiting effectively the microbial growth in vitro. All these results signified that FmLC3 might act as PRR to recognize with a broad specificity for diverse pathogens, and contribute in shrimp immune response via the agglutination, binding and antimicrobial activity.

Lipopolysaccharide-specific binding C-type lectin with one CRD domain from Fenneropenaeus merguiensis (FmLC4) functions as a pattern recognition receptor in shrimp innate immunity

In crustaceans, an innate immune system is solely required because they lack an adaptive immunity. One kind of pattern recognition receptors (PRRs) that plays a particular role in the innate immunity of aquatic shrimp is lectin. A new diverse C-type lectin (FmLC4) was cloned from the hepatopancreas of Fenneropenaeus merguiensis by using RT-PCR and 5' and 3' rapid amplification of cDNA ends approaches. A full-length FmLC4 cDNA comprises 706 bp with an open reading frame of 552 bp, encoding a peptide of 184 amino acids. The predicted primary sequence of FmLC4 consists of a signal peptide of 19 amino acids, a molecular mass of 20.4 kDa, an isoelectric point of 5.13, one carbohydrate recognition domain with a QPD motif and a Ca²⁺ binding site as well as a double-loop characteristic supported by two conserved disulfide bonds. The FmLC4 mRNA expression was found only in the hepatopancreas of normal shrimp and significantly up-regulated upon challenge the shrimp with Vibrio harveyi or white spot syndrome virus (WSSV). Recombinant FmLC4 (rFmLC4) could agglutinate various bacterial strains with Ca²⁺-dependence. Lipopolysaccharide (LPS) could specifically inhibit the agglutinating activity and potently bind to rFmLC4, indicating that FmLC4 was LPS-specific binding C-type lectin. Moreover, rFmLC4 itself displayed the in vivo effective clearance of the pathogenic bacterium V. harveyi. Altogether, FmLC4 may serve as LPS-specific PRR to recognize opportunistic bacterial and viral pathogens, and thus to play a role in the immune defense of aquatic shrimp via the binding and agglutination.

Immune response of anti-lectin Pjlec antibody in freshwater crab Paratelphusa jacquemontii

Sialic acid specific lectin Pjlec isolated from serum of the freshwater crab Paratelphusa jacquemontii served as an antigen for the production of immunoglobulin (Ig) in Balb/c mice sera. Enzyme-linked immunosorbent assay (ELISA) of mice anti-sera with Pjlec lectin affirmed the induction and production of antibody. Anti-Pjlec antibody was isolated from the antisera of mice by Protein A Sepharose affinity chromatography and checked for purity by immunoblot with lectin. Mass spectrometry (MS/MS) of papain digethe peptide sequence of antigen binding fragment (Fab) and fragment crystallizable (Fc). Coatingsted anti-Pjlec revealed of anti-Pjlec to the target cell, rabbit erythrocyte failed to enhance in vitro phagocytosis in the crab. However, inoculation of anti-Pjlec in the hemolymph of the crab elicited in vitro phagocytosis. Proteins in hemocyte lysate supernatant (HLS) were separated by electrophoresis failed to immunoblot with Pjlec or anti-Pjlec. Peptide sequences of trypsin digested lectin protein appeared homologous to deuterostome chordate. The protostome crab that lack the ability to synthesize sialic acid however bind to sialic acid a deuterostome sugar to suggest the complexity in innate immune system of invertebrates. The application of lectin and its antibody require further study on application of pathological conditions associated with alterations in sialylated cell surface.

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.

Identification of a Macrobrachium nipponense C-type lectin with a close evolutionary relationship to vertebrate lectins

C-type lectins (CTLs) are involved in the innate immune defense of vertebrates and invertebrates against invading pathogens. This study cloned and characterized a novel C-type lectin (MnCTL) of the oriental river prawn, Macrobrachium nipponense. The cloned MnCTL cDNA encompasses an open reading frame of 774 nucleotides and encodes polypeptides of 257 residues. The deduced MnCTL protein contains a single carbohydrate recognition domain (CRD) with an EPN (Glu-Pro-Asn) motif in calcium-binding site 2. Phylogenetic analysis indicated that MnCTL has a closer evolutionary relationship with vertebrate lectins than with invertebrate lectins. Tissue expression analysis showed that high levels of MnCTL are ubiquitously distributed in the gills and stomach of M. nipponense. Quantitative real-time RT-PCR (qRT-PCR) analysis showed that MnCTL expression was up-regulated by bacteria or white spot syndrome virus (WSSV) challenge. Knock-down of the MnCTL gene in WSSV-challenged prawns significantly decreased MnALF1 and MnALF2 transcript levels. The recombinant MnCRD (rMnCRD) agglutinated both Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Vibrio parahaemolyticus) in the presence of calcium. Furthermore, rMnCRD could bind to all the tested bacteria with different activities. The sugar-binding assay showed that rMnCRD was able to bind lipopolysaccharide and peptidoglycan in a concentration-dependent manner. In addition, rMnCRD could accelerate bacterial clearance. On the contrary, MnCTL silencing by dsRNA interference could weaken the bacterial clearance ability. All these findings implicated MnCTL were involved in the antiviral and antibacterial innate immunity of M. nipponense.

Long-term influence of cyanobacterial bloom on the immune system of Litopenaeus vannamei

Cyanobacteria are ubiquitously distributed in water on the Earth. It has long been known that the cyanobacterial bloom in aquaculture ponds can cause acute and massive deaths of shrimp. However, the long-term and chronic effects of the cyanobacterial bloom on shrimp are still poorly understood. In this study, the immune state of white pacific shrimp, Litopenaeus vannamei, surviving a naturally occurring cyanobacterial bloom was investigated and tracked for 70 d. Compared with the control, the growth of shrimp suffering high concentrations of cyanobacteria was obviously postponed. In these shrimp, the activities of the NF-κB, JAK/STAT and P38 MAPK immune signaling pathways and the expression of many antimicrobial peptide genes were down-regulated, whereas the expression of C-type lectins was significantly up-regulated. Although the mRNA level of lysozyme was reduced, the expression of the invertebrate-type lysozyme gene was increased. Furthermore, the concentration of hemocytes in hemolymph was greatly decreased, but the phagocytic activity of hemocytes was increased. These suggested that the cyanobacterial bloom has significant and complex influences on the immune system of shrimp, and in turn, alteration of the immune state could be a factor by which few shrimp can survive the cyanobacterial bloom. Thus, the current study could help further understand the interactions between the aquaculture water environment and the immune system of shrimp.

A C-type lectin (MrLec) with high expression in intestine is involved in innate immune response of Macrobrachium rosenbergii

C-type lectins (CTLs) are pattern-recognition proteins that play an important role in innate immunity of vertebrates and invertebrates. In this study, a lectin cDNA named MrLec was cloned and characterized from giant freshwater prawns (Macrobrachiun rosenbergii). The full-length cDNA of MrLec was 1431 bp, which contained an open reading frame of 1041 bp that encoded a protein with 346 amino acids. MrLec was found to contain a typical signal peptide of 18 amino acids and a single carbohydrate-recognition domain with 121 amino acids. The phylogenetic analysis showed that MrLec was grouped with vertebrates and had 57% identity with C-type lectin 3 from Marsupenaeus japonicas. Tissue expression analysis showed that MrLec was ubiquitously distributed at a high level in the intestine, with lower expression levels in the hemocytes, heart, hepatopancreas, gill and stomach. Vibrio parahaemolyticus infection induced the upregulation of MrLec in the gills and intestine. For the white spot syndrome virus (WSSV) challenge, MrLec in gills was upregulated at 24, 36 and 48 h. In intestine, MrLec also went up at 36 and 48 h WSSV challenge. Recombinant MrLec can agglutinate (Ca²⁺-dependent) and bind both Gram-negative and Gram-positive bacteria. rMrLec could attach to lipopolysaccharide and peptidoglycan in a dose-dependent manner. These results indicated possible MrLec involvement in the immune response of giant freshwater prawns.

C-type lectin (MrCTL) from the giant freshwater prawn Macrobrachium rosenbergii participates in innate immunity

C-type lectins (CTLs) play important roles in the innate immunity of invertebrates. In this study, a novel CTL with a single carbohydrate recognition domain (CRD) containing an EPN (Glu-Pro-Asn) motif was identified from the giant freshwater prawn Macrobrachium rosenbergii. This CTL was designated as MrCTL. The cDNA of MrCTL is 1788 bp with a 657 bp open reading frame that encodes a protein of 218 amino acids. The cDNA and genome sequences of MrCTL show a polymorphism that leads to MrCTL isoforms. MrCTL was highly expressed in the gills and intestine of normal prawn, and its transcription increased after Vibrio parahaemolyticus or white spot syndrome virus (WSSV) challenge. Recombinant mature MrCTL and its single CRD could agglutinate (Ca²⁺-dependent) and bind both Gram-positive and Gram-negative bacteria. The recombinant proteins could attach to lipopolysaccharide and peptidoglycan in a dose-dependent manner. Recombinant MrCTL could accelerate bacterial clearance. Thus, MrCTL could serve as a pattern recognition receptor involved in the innate immunity of M. rosenbergii.

Transcriptome Analysis of the Hepatopancreas in the Pacific White Shrimp (Litopenaeus vannamei) under Acute Ammonia Stress

In the practical farming of Litopenaeus vannamei, the intensive culture system and environmental pollution usually results in a high concentration of ammonia, which usually brings large detrimental effects to shrimp, such as increasing the susceptibility to pathogens, reducing growth, decreasing osmoregulatory capacity, increasing the molting frequency, and even causing high mortality. However, little information is available on the molecular mechanisms of the detrimental effects of ammonia stress in shrimp. In this study, we performed comparative transcriptome analysis between ammonia-challenged and control groups from the same family of L. vannamei to identify the key genes and pathways response to ammonia stress. The comparative transcriptome analysis identified 136 significantly differentially expressed genes that have high homologies with the known proteins in aquatic species, among which 94 genes are reported potentially related to immune function, and the rest of the genes are involved in apoptosis, growth, molting, and osmoregulation. Fourteen GO terms and 6 KEGG pathways were identified to be significantly changed by ammonia stress. In these GO terms, 13 genes have been studied in aquatic species, and 11 of them were reported potentially involved in immune defense and two genes were related to molting. In the significantly changed KEGG pathways, all the 7 significantly changed genes have been reported in shrimp, and four of them were potentially involved in immune defense and the other three were related to molting, defending toxicity, and osmoregulation, respectively. In addition, majority of the significantly changed genes involved in nitrogen metabolisms that play an important role in reducing ammonia toxicity failed to perform the protection function. The present results have supplied molecular level support for the previous founding of the detrimental effects of ammonia stress in shrimp, which is a prerequisite for better understanding the molecular mechanism of the immunosuppression from ammonia stress.

Innate immune-stimulating and immune genes up-regulating activities of three types of alginate from Sargassum siliquosum in Pacific white shrimp, Litopenaeus vannamei

The Total Haemocyte Count (THC), phenoloxidase (PO), Superoxide Dismutase (SOD) activity, Phagocytic Activity/Index and Total Protein Plasma (TPP) were examined after feeding the white shrimp Litopenaeus vannamei with diets supplemented with three different types of alginates (acid, calcium and sodium alginates). Immune-related genes expression was evaluated by quantitative Real Time PCR (qRT-PCR). Results indicated that the immune parameters directly increased according to the doses of alginates and time. The 2.0 g kg(-1) of acid and sodium alginate treatments were gave better results. Four immune-related genes expression i.e. LGBP, Toll, Lectin, proPO were up regulated. It is therefore concluded that the supplementation of alginate of Sargassum siliquosum on the diet of L. vannamei enhanced the innate immunity as well as the expression of immune-related genes. It is the first report on the simultaneous evaluation of three alginate types to enhance innate immune parameters and immune-related genes expression in L. vannamei.

Dietary supplementation of probiotic Bacillus PC465 isolated from the gut of Fenneropenaeus chinensis improves the health status and resistance of Litopenaeus vannamei against white spot syndrome virus

This study conducted a 30-day feeding trial and a subsequent 20-day anti-virus infection trial to determine the effects of probiotic Bacillus PC465 on the growth, health status, and disease resistance of Litopenaeus vannamei. Shrimp samples were fed with three practical diets prepared from shrimp feed containing varying probiotic doses [0 (control), 10(7), and 10(9) CFU g(-1)]. Probiotic supplementation significantly increased the weight gain and survival of L. vannamei (p < 0.05). The effect of 10(9) CFU g(-1) on the growth rate was higher than that of 10(7) CFU g(-1). Compared with those in the control group, the activities of digestive enzymes, such as amylase, protease, and lipase, in the shrimp mid-gut significantly increased in the probiotic-fed groups on days 15 and 30, except lipase on day 30. The influence of 10(9) CFU g(-1) on enzyme activities was also greater than that of 10(7) CFU g(-1). Scanning electron microscopy revealed folds and large ravines across the interior surface of the mid-gut, and the number of these folds and ravines increased significantly after the probiotic was administered. The probiotic treatment significantly (p < 0.05) enhanced the transcription of penaeidin 3a (Pen-3a), peroxinectin, C-type lectin 3 (Lec-3), and thioredoxin (Trx) in the hemocytes of L. vannamei. Likewise, probiotic treatment increased the transcription of hemocyanin in the hepatopancreas of L. vannamei. The probiotic treatment also significantly increased the transcription of prophenoloxidase (proPO) but decreased the transcription of crustin in hemocytes. By contrast, the same treatment failed to increase the transcription of Ras-related protein (Rab-6) in hemocytes. The number of species and biomass of Bacillus in the mid-gut were higher in the probiotic-fed group than in the control group. The total biomass of microbes was higher in the shrimp fed with 10(7) CFU g(-1) than in the shrimp fed with 10(9) CFU g(-1) and the control group on days 15 and 30 post-feeding. In two white spot syndrome virus (WSSV) infections, the weight gain, survival, and WSSV copies within the gills of the probiotic-treated shrimp significantly differed (p < 0.05) from those of the control group. Relatively efficient protection was associated with probiotic feeding. Results suggested that Bacillus PC465 feeding improves the growth performance, survival, digestion, and nutrient absorption of L. vannamei. Probiotic treatment also enhances the microbial structures in the gut, promotes the immune status of shrimp, and provides protection against viral infection. The supplementation with 10(9) CFU g(-1) can also improve the growth and survival of L. vannamei.

Critical roles of sea cucumber C-type lectin in non-self recognition and bacterial clearance

C-type lectin is one important pattern recognition receptor (PRR) that plays crucial roles in multiple immune responses. A C-type lectin from sea cucumber Apostichopus japonicus (AjCTL-1) was characterized in the present study. The amino acid sequence of AjCTL-1 shared high similarities with other C-type lectins from invertebrates and vertebrates. The C-type lectin domain (CTLD) of AjCTL-1 contained a Ca(2+)-binding site 2 and four conserved cysteine residues. AjCTL-1 mRNA expression patterns in tissues and after bacterial challenge were then analysed. Quantitative PCR revealed that AjCTL-1 mRNA was widely expressed in the tested tissues of healthy sea cucumber. The highest expression level occurred in gonad followed by body wall, coelomocytes, tentacle, intestinum and longitudinal muscle, and the lowest expression level was in respiratory tree. AjCTL-1 mRNA expression in coelomocytes was significantly induced by gram-negative Listonella anguillarum and gram-positive Micrococcus luteus, with different up-regulation patterns post-challenge. Recombinant AjCTL-1 exhibited the ability to bind peptidoglycan directly, agglutinate M. luteus, Staphylococcus aureus and Escherichia coli, in a Ca(2+)-dependant manner, and enhance the phagocytosis of coelomocytes against E. coli in vitro. The results indicated that AjCTL-1 could act as a PRR in Apostichopus japonicus and had critical roles in non-self recognition and bacterial clearance against invading microbes.

Macrobrachium rosenbergii mannose binding lectin: synthesis of MrMBL-N20 and MrMBL-C16 peptides and their antimicrobial characterization, bioinformatics and relative gene expression analysis

Mannose-binding lectin (MBL), an antimicrobial protein, is an important component of innate immune system which recognizes repetitive sugar groups on the surface of bacteria and viruses leading to activation of the complement system. In this study, we reported a complete molecular characterization of cDNA encoded for MBL from freshwater prawn Macrobrachium rosenbergii (Mr). Two short peptides (MrMBL-N20: (20)AWNTYDYMKREHSLVKPYQG(39) and MrMBL-C16: (307)GGLFYVKHKEQQRKRF(322)) were synthesized from the MrMBL polypeptide. The purity of the MrMBL-N20 (89%) and MrMBL-C16 (93%) peptides were confirmed by MS analysis (MALDI-ToF). The purified peptides were used for further antimicrobial characterization including minimum inhibitory concentration (MIC) assay, kinetics of bactericidal efficiency and analysis of hemolytic capacity. The peptides exhibited antimicrobial activity towards all the Gram-negative bacteria taken for analysis, whereas they showed the activity towards only a few selected Gram-positive bacteria. MrMBL-C16 peptides produced the highest inhibition towards both the Gram-negative and Gram-positive bacteria compared to the MrMBL-N20. Both peptides do not produce any inhibition against Bacillus sps. The kinetics of bactericidal efficiency showed that the peptides drastically reduced the number of surviving bacterial colonies after 24 h incubation. The results of hemolytic activity showed that both peptides produced strong activity at higher concentration. However, MrMBL-C16 peptide produced the highest activity compared to the MrMBL-N20 peptide. Overall, the results indicated that the peptides can be used as bactericidal agents. The MrMBL protein sequence was characterized using various bioinformatics tools including phylogenetic analysis and structure prediction. We also reported the MrMBL gene expression pattern upon viral and bacterial infection in M. rosenbergii gills. It could be concluded that the prawn MBL may be one of the important molecule which is involved in antimicrobial mechanism. Moreover, MrMBL derived MrMBL-N20 and MrMBL-C16 peptides are important antimicrobial peptides for the recognition and eradication of viral and bacterial pathogens.

Reprint of "evolution of specific immunity in shrimp - a vaccination perspective against white spot syndrome virus"

Invertebrates lack true adaptive immunity and it solely depends on the primitive immunity called innate immunity. However, various innate immune molecules and mechanisms are identified in shrimp that plays potential role against invading bacterial, fungal and viral pathogens. Perceiving the shrimp innate immune mechanisms will contribute in developing effective vaccine strategies against major shrimp pathogens. Hence this review intends to explore the innate immune molecules of shrimp with suitable experimental evidences together with the evolution of "specific immune priming" of invertebrates. In addition, we have emphasized on the development of an effective vaccine strategy against major shrimp pathogen, white spot syndrome virus (WSSV). The baculovirus displayed rVP28 (Bac-VP28), a major envelope protein of WSSV was utilized to study its vaccine efficacy by oral route. A significant advantage of this baculovirus expression cassette is the use of WSSV-immediate early 1 (ie1) promoter that derived the abundant expression of rVP28 protein at the early stage of the infection in insect cell. The orally vaccinated shrimp with Bac-VP28 transduced successfully in the shrimp cells as well as provided highest survival rate. In support to our vaccine efficacy we analysed Pattern Recognition Proteins (PRPs) β-1,3 glucan lipopolysaccharides (LGBP) and STAT gene profiles in the experimental shrimp. Indeed, the vaccination of shrimp with Bac-VP28 demonstrated some degree of specificity with enhanced survival rate when compared to control vaccination with Bac-wt. Hence it is presumed that the concept of "specific immune priming" in relevant to shrimp immunity is possible but may not be common to all shrimp pathogens.

Evolution of specific immunity in shrimp - a vaccination perspective against white spot syndrome virus

Invertebrates lack true adaptive immunity and it solely depends on the primitive immunity called innate immunity. However, various innate immune molecules and mechanisms are identified in shrimp that plays potential role against invading bacterial, fungal and viral pathogens. Perceiving the shrimp innate immune mechanisms will contribute in developing effective vaccine strategies against major shrimp pathogens. Hence this review intends to explore the innate immune molecules of shrimp with suitable experimental evidences together with the evolution of "specific immune priming" of invertebrates. In addition, we have emphasized on the development of an effective vaccine strategy against major shrimp pathogen, white spot syndrome virus (WSSV). The baculovirus displayed rVP28 (Bac-VP28), a major envelope protein of WSSV was utilized to study its vaccine efficacy by oral route. A significant advantage of this baculovirus expression cassette is the use of WSSV-immediate early 1 (ie1) promoter that derived the abundant expression of rVP28 protein at the early stage of the infection in insect cell. The orally vaccinated shrimp with Bac-VP28 transduced successfully in the shrimp cells as well as provided highest survival rate. In support to our vaccine efficacy we analysed Pattern Recognition Proteins (PRPs) β-1,3 glucan lipopolysaccharides (LGBP) and STAT gene profiles in the experimental shrimp. Indeed, the vaccination of shrimp with Bac-VP28 demonstrated some degree of specificity with enhanced survival rate when compared to control vaccination with Bac-wt. Hence it is presumed that the concept of "specific immune priming" in relevant to shrimp immunity is possible but may not be common to all shrimp pathogens.

Identification of a C-type lectin with antiviral and antibacterial activity from pacific white shrimp Litopenaeus vannamei

C-type lectins (CTLs) play crucial roles in innate immune responses in invertebrates by recognizing and eliminating microinvaders. In this study, a CTL from pacific white shrimp Litopenaeus vannamei (LvCTL3) was identified. LvCTL3 contains a single C-type lectin-like domain (CTLD), which shows similarities to those of other shrimp CTLs and has a mutated 'EPD' motif in Ca(2+)-binding site 2. LvCTL3 mRNA can be detected in all tested tissues and expression of LvCTL3 in gills was up-regulated after Lipopolysaccharides, poly (I:C), Vibrio parahaemolyticus and white spot syndrome virus (WSSV) challenges, suggesting activation responses of LvCTL3 to bacterial, virus and immune stimulant challenges. The 5'flanking regulatory region of LvCTL3 was cloned and we identified a NF-κB binding motif in the LvCTL3 promoter region. Dual-luciferase reporter assays indicated that over-expression of L. vannamei dorsal can dramatically up regulate the promoter activity of LvCTL3, suggesting that LvCTL3 expression could be regulated through NF-κB signaling pathway. As far as we know, this is the first report on signaling pathway involve in shrimp CTLs expression. The recombinant LvCTL3 protein was expressed in Escherichia coli and purified by Ni-affinity chromatography. The purified LvCTL3 can agglutinate Gram-negative microbe Vibrio alginolyticus and V. parahaemolyticus and Gram-positive bacteria Bacillus subtilis in the presence of calcium ions, but cannot agglutinate Gram-positive bacteria Streptococcus agalactiae. The agglutination activity of LvCTL3 was abolished when Ca(2+) was chelated with EDTA, suggesting the function of LvCTL3 is Ca(2+)-dependent. In vivo challenge experiments showed that the recombinant LvCTL3 protein can significantly reduce the mortalities of V. parahemolyticus and WSSV infection, indicating LvCTL3 might play significant roles in shrimp innate immunity defense against bacterial and viral infection.

Function of two novel single-CRD containing C-type lectins in innate immunity from Eriocheir sinensis

C-type lectin is one of the pattern-recognition proteins of the non-self-innate immune system in invertebrates. In this study, two novel C-type lectin cDNAs (EsCTL1 and EsCTL2) of Eriocheir sinensis were cloned and characterized. EsCTL1 has 169 amino acids, whereas EsCTL2 has 164 amino acids. These two lectins contain one carbohydrate-recognition domain. Phylogenetic analysis showed that EsCTL1 and EsCTL2 were not clustered with other reported lectins from crabs. EsCTL1 and EsCTL2 were expressed only in the hepatopancreas, as detected by real-time PCR. When healthy crabs were challenged with lipopolysaccharide (LPS), peptidoglycan (PGN), Staphylococcus aureus, or Aeromonas hydrophila, the expression levels of EsCTL1 and EsCTL2 were significantly regulated. The recombinant EsCTL1 and EsCTL2 can agglutinate both Gram-positive (S. aureus) and Gram-negative bacteria (Vibrio parahaemolyticus and A. hydrophila) in a Ca2+ -dependent manner. The recombinant EsCTL1 and EsCTL2 can directly bind to LPS and PGN and to all tested microorganisms (S. aureus, Bacillus thuringiensis, Bacillus subtilis, Escherichia coli, Vibrio natriegens, V. parahaemolyticus, and A. hydrophila). Furthermore, rEsCTL1 and rEsCTL2 may facilitate the clearance of V. parahaemolyticus in vivo. These results suggest that EsCTL1 and EsCTL2 may have important roles in the anti-bacterial immunity of Chinese mitten crab.

RNA-Seq analysis reveals genes associated with resistance to Taura syndrome virus (TSV) in the Pacific white shrimp Litopenaeus vannamei

Outbreak of Taura syndrome virus (TSV) is one of the major pathogens of the Pacific white shrimp Litopenaeus vannamei. Although selective breeding for improvement of TSV resistance in L. vannamei has been successfully developed and has led to a great benefit to the shrimp farming industry worldwide. The molecular mechanisms underlying the viral resistance in shrimp remain largely unknown. In the present study, we conducted the first transcriptomic profiling of host responses in hemolymph and hemocytes in order to identify the differentially expressed genes associated with resistance to TSV in L. vannamei. High-throughput RNA-Seq was employed, obtaining 193.6 and 171.2 million high-quality Illumina reads from TSV-resistant and susceptible L. vannamei lines respectively. A total of 61,937 contigs were generated with an average length of 546.26 bp. BLASTX-based gene annotation (E-value < 10(-5)) allowed the identification of 12,398 unique proteins against the NCBI non-redundant NR database. In addition, comparison of digital gene expression between resistant and susceptible strains revealed 1374 significantly differentially expressed contigs (representing 697 unigenes). Gene pathway analysis of the differentially expressed gene set highlighted several putative genes involved in the immune response activity including (1) pathogen/antigen recognition including immune regulator, adhesive protein and signal transducer; (2) coagulation; (3) proPO pathway cascade; (4) antioxidation; and (5) protease. The expression patterns of 22 differentially expressed genes involving immune response were validated by quantitative real-time RT-PCR (average correlation coefficients 0.94, p-value < 0.001). Our results provide valuable information on gene functions associated with resistance to TSV in L. vannamei.

A preliminary study of differentially expressed genes of the scallop Chlamys farreri against acute viral necrobiotic virus (AVNV)

The scallop Chlamys farreri is one of the most important aquaculture species in northern coastal provinces. However, the sustainable development of scallop industry is currently threatened by a notorious pathogen named as acute viral necrobiotic virus (AVNV), which often causes mass mortality of the animals. Despite that great attention has been focused on this novel pathogen, little knowledge about the host-virus interactions is available. In this study, suppression subtractive hybridization (SSH) was employed to identify the up-regulated differentially expressed genes in the hemocytes of C. farreri challenged by AVNV. A forward subtracted cDNA library was finally constructed and 288 positive colonies representing differentially genes were screened to perform sequencing. A total of 275 ESTs were used for further analysis using bioinformatics tools after vector screening, among which 167 ESTs could be finally identified, with significant match (E values <1 × 10(-3)) to the deposited genes (proteins) in the corresponding databases. These genes could be classified into ten categories according to their Gene Ontology annotations of biological processes and molecular functions, i.e. cell defense and homeostasis (13.82%), cellular protein metabolic process (14.90), cellular metabolism (13.09%), cytoskeletal or cellular component (5.82%), transcription regulation or RNA processing (2.18%), cell division (meiosis)/apoptosis (2.18%), DNA metabolic process and repair (1.45%), cell adhesion/signaling (1.09%), microsatellite (0.73%), and ungrouped or unknown functions (6.88). The possible biological significance of some novel genes (mainly immune and homeostasis related genes) in the host response to AVNV were discussed. This study is the first global analysis of differentially expressed genes in hemocytes from AVNV-infected C. farreri, and in addition to increasing our understanding of the molecular pathogenesis of this virus-associated scallop disease, the results presented here should provide new insights into the molecular basis of host-pathogen interactions in C. farreri.

Discovery of immune molecules and their crucial functions in shrimp immunity

Several immune-related molecules in penaeid shrimps have been discovered, most of these via the analysis of expressed sequence tag libraries, microarray studies and proteomic approaches. These immune molecules include antimicrobial peptides, serine proteinases and inhibitors, phenoloxidases, oxidative enzymes, clottable protein, pattern recognition proteins, lectins, Toll receptors, and other humoral factors that might participate in the innate immune system of shrimps. These molecules have mainly been found in the hemolymph and hemocytes, which are the main sites where immune reactions take place, while some are found in other immune organs/tissues, such as the lymphoid organs, gills and intestines. Although the participation of some of these immune molecules in the shrimp innate immune defense against invading pathogens has been demonstrated, the functions of many molecules remain unclear. This review summarizes the current status of our knowledge concerning the discovery and functional characterization of the immune molecules in penaeid shrimps.

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.

Transcriptome analysis of Pacific white shrimp (Litopenaeus vannamei) hepatopancreas in response to Taura syndrome Virus (TSV) experimental infection

Background

The Pacific white shrimp, Litopenaeus vannamei, is a worldwide cultured crustacean species with important commercial value. Over the last two decades, Taura syndrome virus (TSV) has seriously threatened the shrimp aquaculture industry in the Western Hemisphere. To better understand the interaction between shrimp immune and TSV, we performed a transcriptome analysis in the hepatopancreas of L. vannamei challenged with TSV, using the 454 pyrosequencing (Roche) technology.

Methodology/Principal Findings

We obtained 126919 and 102181 high-quality reads from TSV-infected and non-infected (control) L. vannamei cDNA libraries, respectively. The overall de novo assembly of cDNA sequence data generated 15004 unigenes, with an average length of 507 bp. Based on BLASTX search (E-value <10−5) against NR, Swissprot, GO, COG and KEGG databases, 10425 unigenes (69.50% of all unigenes) were annotated with gene descriptions, gene ontology terms, or metabolic pathways. In addition, we identified 770 microsatellites and designed 497 sets of primers. Comparative genomic analysis revealed that 1311 genes differentially expressed in the infected shrimp compared to the controls, including 559 up- and 752 down- regulated genes. Among the differentially expressed genes, several are involved in various animal immune functions, such as antiviral, antimicrobial, proteases, protease inhibitors, signal transduction, transcriptional control, cell death and cell adhesion.

Conclusions/Significance

This study provides valuable information on shrimp gene activities against TSV infection. Results can contribute to the in-depth study of candidate genes in shrimp immunity, and improves our current understanding of this host-virus interaction. In addition, the large amount of transcripts reported in this study provide a rich source for identification of novel genes in shrimp.

Susceptibility of juvenile Macrobrachium rosenbergii to different doses of high and low virulence strains of white spot syndrome virus (WSSV)

As some literature on the susceptibility of different life stages of Macrobrachium rosenbergii to white spot syndrome virus (WSSV) is conflicting, the pathogenesis, infectivity and pathogenicity of 2 WSSV strains (Thai-1 and Viet) were investigated here in juveniles using conditions standardized for Penaeus vannamei. As with P. vannamei, juvenile M. rosenbergii (2 to 5 g) injected with a low dose of WSSV-Thai-1 or a high dose of WSSV-Viet developed comparable clinical pathology and numbers of infected cells within 1 to 2 d post-infection. In contrast, a low dose of WSSV-Viet capable of causing mortality in P. vannamei resulted in no detectable infection in M. rosenbergii. Mean prawn infectious dose 50% endpoints (PID₅₀ ml⁻¹) determined in M. rosenbergii were in the order of 100-fold higher for WSSV-Thai-1 (105.3 ± 0.4 PID₅₀ ml⁻¹) than for WSSV-Viet (103.2 ± 0.2 PID₅₀ ml⁻¹), with each of these being about 20-fold and 400-fold lower, respectively, than found previously in P. vannamei. The median lethal dose (LD₅₀ ml⁻¹) determined in M. rosenbergii was also far higher (~1000-fold) for WSSV-Thai-1 (105.4 ± 0.4 LD₅₀ ml⁻¹) than for WSSV-Viet (102.3 ± 0.3 LD₅₀ ml⁻¹). Based on these data, it is clear that juvenile M. rosenbergii are susceptible to WSSV infection, disease and mortality. In comparison to P. vannamei, however, juvenile M. rosenbergii appear more capable of resisting infection and disease, particularly in the case of a WSSV strain with lower apparent virulence.