Immunological responses of Penaeus monodon to DNA vaccine and its efficacy to protect shrimp against white spot syndrome virus (WSSV)

Experimental Infection Models and Their Usefulness for White Spot Syndrome Virus (WSSV) Research in Shrimp

White spot syndrome virus (WSSV) is marked as one of the most economically devastating pathogens in shrimp aquaculture worldwide. Infection of cultured shrimp can lead to mass mortality (up to 100%). Although progress has been made, our understanding of WSSV's infection process and the virus-host-environment interaction is far from complete. This in turn hinders the development of effective mitigation strategies against WSSV. Infection models occupy a crucial first step in the research flow that tries to elucidate the infectious disease process to develop new antiviral treatments. Moreover, since the establishment of continuous shrimp cell lines is a work in progress, the development and use of standardized in vivo infection models that reflect the host-pathogen interaction in shrimp is a necessity. This review critically examines key aspects of in vivo WSSV infection model development that are often overlooked, such as standardization, (post)larval quality, inoculum type and choice of inoculation procedure, housing conditions, and shrimp welfare considerations. Furthermore, the usefulness of experimental infection models for different lines of WSSV research will be discussed with the aim to aid researchers when choosing a suitable model for their research needs.

The plasticity of immune memory in invertebrates

Whether specific immune protection after initial pathogen exposure (immune memory) occurs in invertebrates has long been uncertain. The absence of antibodies, B-cells and T-cells, and the short lifespans of invertebrates led to the hypothesis that immune memory does not occur in these organisms. However, research in the past two decades has supported the existence of immune memory in several invertebrate groups, including Ctenophora, Cnidaria, Nematoda, Mollusca and Arthropoda. Interestingly, some studies have demonstrated immune memory that is specific to the parasite strain. Nonetheless, other work does not provide support for immune memory in invertebrates or offers only partial support. Moreover, the expected biphasic immune response, a characteristic of adaptive immune memory in vertebrates, varies within and between invertebrate species. This variation may be attributed to the influence of biotic or abiotic factors, particularly parasites, on the outcome of immune memory. Despite its critical importance for survival, the role of phenotypic plasticity in immune memory has not been systematically examined in the past two decades. Additionally, the features of immune responses occurring in diverse environments have yet to be fully characterized.

RNAi-Based Therapy: Combating Shrimp Viral Diseases

Shrimp aquaculture has become a vital industry, meeting the growing global demand for seafood. Shrimp viral diseases have posed significant challenges to the aquaculture industry, causing major economic losses worldwide. Conventional treatment methods have proven to be ineffective in controlling these diseases. However, recent advances in RNA interference (RNAi) technology have opened new possibilities for combating shrimp viral diseases. This cutting-edge technology uses cellular machinery to silence specific viral genes, preventing viral replication and spread. Numerous studies have shown the effectiveness of RNAi-based therapies in various model organisms, paving the way for their use in shrimp health. By precisely targeting viral pathogens, RNAi has the potential to provide a sustainable and environmentally friendly solution to combat viral diseases in shrimp aquaculture. This review paper provides an overview of RNAi-based therapy and its potential as a game-changer for shrimp viral diseases. We discuss the principles of RNAi, its application in combating viral infections, and the current progress made in RNAi-based therapy for shrimp viral diseases. We also address the challenges and prospects of this innovative approach.

Efficacy of White Spot Syndrome Virus Protein VP28-Expressing Chlorella vulgaris as an Oral Vaccine for Shrimp

The white spot syndrome virus (WSSV) is the causative agent of white spot disease, which kills shrimp within a few days of infection. Although WSSV has a mortality rate of almost 100% and poses a serious threat to the shrimp farming industry, strategies for its prevention and treatment are extremely limited. In this study, we examined the efficacy of VP28, a recombinant WSSV protein expressed in Chlorella vulgaris (C. vulgaris), as an oral shrimp vaccine. When compared with the control group, in which WSSV had a cumulative mortality of 100%, shrimp treated with 5% VP28-expressing C. vulgaris in their feed only had a 20% cumulative mortality rate 12 days after the WSSV challenge. When compared with the nonvaccinated group, the transcription of anti-lipopolysaccharide factor, C-type lectin, and prophenoloxidase genes, which are involved in shrimp defense against WSSV infection, was upregulated 29.6 fold, 15.4 fold, and 11.5 fold, respectively. These findings highlight C. vulgaris as a potential host for industrial shrimp vaccine production.

Determination of the efficacy of using a serine protease gene as a DNA vaccine to protect against Vibrio parahaemolyticus infection in Litopenaeus vannamei

Serine proteases are proteolytic enzymes that exhibit biological roles in many biological systems. Previously, a Vibrio parahaemolyticus serine protease was reported to be a virulence factor. Here, the serine protease gene of V. parahaemolyticus was investigated as a DNA vaccine against V. parahaemolyticus in Litopenaeus vannamei. The serine protease gene was mutated to replace the conserved residues His82, Asp131 and Ser231 with Gly, Asp and Pro, respectively. Then, a pcDNA3.1 vector to express mutVpSP (mutant serine protease) was constructed for in vitro and in vivo DNA vaccine investigation. In vivo mutVpSP transcriptional analysis revealed expression in various immunized white shrimp tissues, such as hemocytes, hepatopancreas, stomach, intestine, gills, and muscle. The efficiency of prevention of V. parahaemolyticus infection was investigated in vaccinated shrimp, and the lowest cumulative mortality percentage was 30%, while the control shrimp had a 60% cumulative mortality rate. The immune system was stimulated in shrimp vaccinated with the DNA vaccine. The mRNA expression of the shrimp immune-responsive genes phenoloxidase, peroxinectin and C-type lectin was significantly upregulated. Additionally, the humoral and cellular immune responses, including the PO, phagocytic, and encapsulation activities and nodule formation, were elevated. These results suggested that the serine protease could be a V. parahaemolyticus virulence determinant and that this DNA vaccine could be applied as an effective vaccine candidate for control of acute hepatopancreatic necrosis disease syndrome (AHPND) in shrimp.

Construction of an easily detectable transgenic Synechococcus elongatus PCC 7942 against White Spot Syndrome Virus using vp28 and mOrange Gene and its metabolism in shrimp

White spot syndrome is an epidemic disease caused by the highly contagious and lethal white spot syndrome virus (WSSV), resulting in huge economic losses to the global aquaculture industry. VP28 is the main structural protein in the capsule of WSSV and is important in the early stage of infection. Under an excitation wavelength of 548 nm, the mOrange fluorescent protein releases a 562 nm emission wavelength, which is different from the autofluorescence of cyanobacteria. Therefore, using this characteristic combined with the receptor system of Synechococcus elongatus PCC 7942, we constructed transgenic S. elongatus to express the recombinant protein VP28-mOrange. In addition, PCR and western blotting were used to confirm the stable expression of the target gene in cyanobacteria. Using mOrange tracer features, we explored the recombinant protein VP28-mOrange in the metabolic cycle of young Litopenaeus Vannamei after feeding. After the young shrimp had stopped consuming transgenic cyanobacteria, the 24 to 33 h fluorescence signal in the intestine was very weak, and almost disappeared after 36 h. We explored the protective effect of transgenic vp28-mOrange S. elongatus within 48 h of being ingested by L. vannamei and set WSSV challenges at 2, 12, 24, and 48 h post-immunization. However, the survival rate of L. vannamei decreased as the time of the WSSV challenge increased. The survival rate on the seventh day was 81%, 52%, 45.5%, and 33.3% for shrimps challenged for 2, 12, 24, and 48 h, respectively. Enzyme activity can also support this conjecture, the enzyme activity indexes of the experimental groups were significantly reduced compared to positive and wild-type controls. Therefore, this immune agent functioned as a preventive agent. Compared with the traditional method, this method was easy to detect and can visualize the digestion of transgenic cyanobacteria in the Litopenaeus vannamei intestine.

Monoclonal antibodies (mAbs) and single chain variable fragment (scFv) antibodies targeting envelope protein VP28 of white spot syndrome virus provide protection against viral infection

White spot syndrome virus (WSSV) is extremely pathogenic and causes huge economic losses in the shrimp farming industry. Neutralizing antibodies against WSSV is expected to be an effective means of preventing infection with the virus. In the present study, eight monoclonal antibodies (mAbs) against VP28 were developed by immunizing BALB/c mice with WSSV-VP28 recombinant protein. Among them, three mAbs named 3B7, 2G3 and 5D2 were determined to be able to delay the mortality of WSSV-infected shrimp in vivo neutralization assay, suggesting their neutralizing ability against WSSV infection. Immunoblotting results showed that the three mAbs reacted specifically with native VP28 of WSSV, and could also recognize the virions in the gills of WSSV-infected shrimp by IFA. Furthermore, the single chain variable fragment (scFv) genes specific for WSSV-VP28 were cloned from the three hybridoma cells and expressed in Escherichia coli. After purification and refolding, three biologically active scFv recombinant proteins were all capable of recognizing the native VP28 of WSSV and delayed the mortality of WSSV-infected shrimp, indicating their neutralizing capacity against WSSV. Subsequently, the eukaryotic expression plasmids of three scFv genes were constructed and the transcriptional properties of expression vectors in shrimp were analyzed. Animal experiments also proved that the scFv eukaryotic expression plasmids were able to partially neutralize WSSV infection. Thus, the production of neutralizing mAb and recombinant scFv antibodies against WSSV has a promising therapeutic potential in prevention and treatment of white spot disease of shrimp.

Innate immune memory in invertebrates: Concept and potential mechanisms

Invertebrates are the protagonists of a recent paradigm shift because they now show that vertebrates are not the only group with immune memory. This review discusses the concept of immune priming, its characteristics, and differences with trained immunity and immune enhancement. We include an update of the current status of immune priming within generations in different groups of invertebrates which now include work in 5 Phyla: Ctenophora, Cnidaria, Mollusca, Nematoda, and Arthropoda. Clearly, few Phyla have been studied. We also resume and discuss the effector mechanism related to immune memory, including integrating viral elements into the genome, endoreplication, and epigenetics. The roles of other elements are incorporated, such as hemocytes, immune pathways, and metabolisms. We conclude that taking care of the experimental procedure will discern if results provide or do not support the invertebrates' immune memory and that regarding mechanisms, indeed, there are no studies on the immune memory mechanisms, this is how specificity is reached, and how and where the immune memory is stored and how is recall upon subsequent encounters. Finally, we discuss the possibility of having more than one mechanism working in different groups of invertebrates depending on the environmental conditions.

Oral delivery of pVAX-OMP and pVAX-hly DNA vaccine using chitosan-tripolyphosphate (Cs-TPP) nanoparticles in Rohu, (Labeo rohita) for protection against Aeromonas hydrophila infection

The present study examines the effectiveness of DNA vaccine against Aeromonas hydrophila through oral route using chitosan-tripolyphosphate (Cs-TPP) nanoparticles encapsulation. The virulent gene of outer membrane protein (OMP) and hemolysin (hly) related to pathogenicity of A. hydrophila was used to construct a DNA vaccine using pVAX1, and the construct was named as pVAX-OMP and pVAX-hly DNA vaccines. The pVAX-OMP and pVAX-hly DNA vaccines were encapsulated by Cs-TPP nanoparticles and size measured by field emission scanning electron microscopy (FE-SEM). The encapsulation efficiency of Cs-TPP nanoparticles was found to be 79.6% for pVAX-OMP DNA and 82.3% for pVAX-hly DNA binding with Cs-TPP nanoparticles. The stability and invitro release profile of plasmid DNA was also determined after encapsulation using DNase and chitosanase. DNA vaccines distribution in tissues was investigated in fish fed with the pVAX-OMP, pVAX-hly and pVAX-OMP+pVAX-hly encapsulated in Cs-TPP nanoparticles and confirmed by PCR and multiplex PCR. The results suggest that Cs-TPP nanoparticles encapsulated DNA vaccine delivered into fish by feeding. After oral vaccination of Labeo rohita were challenged with A. hydrophila by intraperitoneal injection. Relatively, gene expression of c- and g-type lysozyme followed by pro- and anti-inflammatory cytokines (Interlukin-10 and Tumor Growth Factor β) was up-regulated in heart and kidney for pVAX-OMP+pVAX-hly vaccinated group. Moreover, fish fed with pVAX-OMP+pVAX-hly encapsulated in Cs-TPP nanoparticles had a significantly higher survival rate (76.2%) against A. hydrophila. This study concludes that pVAX-OMP and pVAX-hly DNA vaccines can be delivered orally using Cs-TPP nanoparticles for protection against A. hydrophilainfection.

Silencing of prophenoloxidase (proPO) gene in freshwater prawn, Macrobrachium rosenbergii, makes them susceptible to white spot syndrome virus (WSSV)

Prophenoloxidase (proPO) is very important to protect the invertebrates from microbial infections. Our previous studies revealed that proPO was up-regulated in WSSV-injected Macrobrachium rosenbergii and is responsible for protecting M. rosenbergii from WSSV. In order to prove this mechanism, an attempt was made in the present study to silence the proPO gene in freshwater prawn by injection of dsRNA-proPO followed by WSSV challenge. Two partial fragments of proPO with the size of 251 and 331 bp were used to synthesize dsRNA using LITMUS38i vector and E. coli. The bacterially synthesized dsRNA-proPO was used to silence proPO gene to determine its involvement in developing resistance in prawn against WSSV. In proPO gene-silenced prawn, 100% mortality was observed after WSSV challenge whereas no mortality was observed in prawn injected with WSSV alone. The WSSV infection in gene-silenced prawn was confirmed by PCR, and its propagation was quantified by ELISA and real-time PCR at different time intervals. Real-time PCR assay revealed a significant reduction in the expression of proPO gene in WSSV-challenged proPO-silenced prawn when compared to normal prawn. Level of proPO was reduced significantly in the haemolymph of proPO-silenced prawn when compared to prawn injected with PBS.

Pandanus tectorius fruit extract promotes Hsp70 accumulation, immune-related genes expression and Vibrio parahaemolyticus tolerance in the white-leg shrimp Penaeus vannamei

Plants and herbal extracts are indispensable for controlling the spread of disease-causing bacteria, including those that infect aquatic organisms used in aquaculture. The use of plant or herbal extract is expected to be safe for aquatic animals and less harmful to the environment, as opposed to conventional therapeutic alternatives such as antibiotics that promote the occurrence of potential antibiotic-resistant bacteria when used improperly. The efficacy of Pandanus tectorius fruit extract in the regulation of Hsp70 expression, pro-phenoloxidase (ProPO), peroxinectin, penaeidin, crustin and transglutaminase, all immune peptides essential for Vibrio tolerance in white leg shrimp, Penaeus vannamei, was investigated in this study, which included the determination of the safety levels of the extract. Tolerance of shrimp against Vibrio parahaemolyticus, a pathogenic bacteria that causes Acute Hepatopancreas Necrosis Disease (AHPND), was assessed on the basis of median lethal dose challenge survival (LD50 = 10⁶ cells/ml). Mortality was not observed 24 h after exposure of 0.5-6 g/L of the fruit extract, indicating that P. tectorius was not toxic to shrimp at these concentrations. A 24-h incubation of 2-6 g/L of the fruit extract increased shrimp tolerance to V. parahaemolyticus, with survival doubled when the maximum dose tested in this study was used. Concomitant with a rise in survival was the increase in immune-related proteins, with Hsp70, ProPO, peroxinectin, penaeidin, crustin and transglutaminase increased 10, 11, 11, 0.4, 8 and 13-fold respectively. Histological examination of the hepatopancreas and muscle tissues of Vibrio-infected shrimp primed with P. tectorius extract revealed reduced signs of histopathological degeneration, possibly due to the accumulation of Hsp70, a molecular chaperone crucial to cellular protein folding, tissue repair and immune response of living organisms, including Penaeid shrimp.

Effective suppression of yellow head virus replication in Penaeus monodon hemocytes using constitutive expression vector for long-hairpin RNA (lhRNA)

Double-stranded RNA (dsRNA) is employed to down-regulate the expression of specific genes of shrimp viral pathogens through the RNA interference (RNAi) pathway. The administration of dsRNA into shrimp has been shown to be an effective strategy to block yellow head virus (YHV) progression. In this study, a vector (pLVX-AcGFP1-N1) was developed to introduce a long-hairpin RNA (lhRNA) silencing cassette under a CMV promoter, so-called "pLVX-lhRdRp", against the RNA-dependent RNA polymerase (RdRp) gene of YHV. A primary culture of hemocytes isolated from Penaeus monodon was transfected with the pLVX-lhRdRp vector, generating transcripts of lhRNAs as early as 12 h post transfection. Twelve hours prior to YHV challenge, the primary hemocyte cell culture was transfected with pLVX-lhRdRp, whereas control groups were transfected with pLVX-AcGFP1-N1 or no transfection. The group treated with pLVX-lhRdRp significantly suppressed YHV replication at 24-72 h after YHV challenge. The results from RT-PCR and immunohistochemistry confirmed that both mRNA and protein expression of YHV were effectively inhibited by the pLVX-lhRdRp vector. Thus, our hemocyte culture and dsRNA expression plasmid with constitutive promoter have potential as a platform to test DNA constructs expressing long-hairpin RNA against pathogenic viral infection and as a RNAi-based DNA vaccine in shrimp.

Marine actinomycetes Nocardiopsis alba MCCB 110 has immunomodulatory property in the tiger shrimp Penaeus monodon

Shrimp farming constitutes an important source of revenue and employment in many developing countries. However, the shrimp industry has always been plagued with infectious diseases having varied aetiologies. Dominated by non - specific immune mechanism, preventive health care strategy is the most appropriate approach to protect the crop. The present study evaluated the efficacy of an actinomycete, Nocardiopsis alba MCCB 110 in eliciting non - specific immune mechanism in Penaeus monodon having Vibrio harveyi as the challenge organism. Haemocyte count, total protein, phenoloxidase, reactive oxygen intermediates, acid and alkaline phosphatase as well as the gene expression of proPO, peroxinectin, transglutaminase, alpha 2-macroglobulin, astakine, crustin, and penaeidin-3 were evaluated. The results demonstrated that the phenoloxidase, respiratory burst, total protein, acid and alkaline phosphatases were higher in the haemolymph of shrimps fed with Nocardiopsis alba MCCB 110 incorporated feed before and after challenge with Vibrio harveyi, compared to those of placebo fed animals. Up-regulation of six immune genes (alpha 2 macroglobulin, penaeidin -3, transglutaminase, proPO, crustin and peroxinectin) during the post-challenge were recorded. Survival of shrimp among the Nocardiopsis alba administered ones was 83% while it was 50% in placebo fed group. The elevated levels of nonspecific immune gene transcripts and concurrent increase in non specific immunity besides the higher survival rate in the Nocardiopsis alba administered group demonstrated the immunomodulatory property of the marine actinomycete Nocardiopsis alba MCCB 110 in the tiger shrimp Penaeus monodon, and on administering it through diet shrimp could be protected from vibriosis especially of V. harveyi.

Macrobrachium rosenbergii Cu/Zn superoxide dismutase (Cu/Zn SOD) expressed in Saccharomyces cerevisiae and evaluation of the immune function to Vibrio parahaemolyticus

Superoxide dismutases (SODs) are important antioxidant enzymes that occur in virtually all oxygen-respiring organisms, and copper/zinc SOD (Cu/ZnSOD) is one of the most important SODs. In the present study, Macrobrachium rosenbergii Cu/Zn-SOD was expressed in a yeast eukaryotic system. The open reading frame (ORF) of MrCu/ZnSOD was cloned into the plasmid vector pHAC181, and the recombinant plasmid was integrated into the downstream region of the GAL1 promoter in Saccharomyces cerevisiae strain GAL1-ScRCH1 via homologous recombination. The resulting recombinant MrCu/ZnSOD consisted of a 3 × HA-tag at its C-terminal. Via western blot, the molecular weight of the recombinant MrCu/ZnSOD was estimated at about 30 kDa. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of this recombinant MrCu/ZnSOD ranged from 0.556 to 0.840 μM, and from 0.967 to 2.015 μM, respectively. The recombinant MrCu/ZnSOD protein was able to agglutinate four Gram-negative bacterial strains, as well as two of three Gram-positive strains (except Staphylococcus aureus). This demonstrated that the recombinant protein possessed some antimicrobial activity against certain Gram-positive and Gram-negative bacteria. M. rosenbergii were fed with the recombinant yeast strain MrCu/ZnSOD for 4 weeks and then challenged with the most common crustacean pathogen, Vibrio parahaemolyticus. This group of prawns presented lower mortality, higher enzymatic activity, and higher expression of the mRNA of immune-related genes than that in the control groups. Taken together, these results suggest that MrCu/ZnSOD is an antioxidant enzyme and antimicrobial peptide involved in the crustacean innate immune system and offers protection to the host against pathogenic bacteria.

Meta-analysis of antiviral protection of white spot syndrome virus vaccine to the shrimp

Currently, white spot syndrome virus (WSSV) is one of the most serious pathogens that impacts shrimp farming around the world. A WSSV vaccine provides a significant protective benefit to the host shrimp. Although various types of vaccines against WSSV have emerged, the immune effects among them were not compared, and it remains unclear which type of vaccine has the strongest protective effect. Meanwhile, due to the lack of effective routes of administration and immunization programs, WSSV vaccines have been greatly limited in the actual shrimp farming. To answer these questions, this study conducted a comprehensive meta-analysis over dozens of studies and compared all types WSSV vaccines, which include sub-unit protein vaccines, whole virus inactivated vaccines, DNA vaccines and RNA-based vaccines. The results showed that the RNA-based vaccine had the highest protection rate over the other three types of vaccines. Among the various sub-unit protein vaccines, VP26 vaccine had the best protective effects than other sub-unit protein vaccines. Moreover, this study demonstrated that vaccines expressed in eukaryotic hosts had higher protection rates than that of prokaryotic systems. Among the three immunization modes (oral administration, immersion and injection) used in monovalent protein vaccines, oral administration had the highest protection rate. In natural conditions, shrimp are mostly infected by the virus orally. These results provide a guide for exploration of a novel WSSV vaccine and help facilitate the application of WSSV vaccines in shrimp farming.

A transcriptome study on Macrobrachium nipponense hepatopancreas experimentally challenged with white spot syndrome virus (WSSV)

White spot syndrome virus (WSSV) is one of the most devastating pathogens of cultured shrimp, responsible for massive loss of its commercial products worldwide. The oriental river prawn Macrobrachium nipponense is an economically important species that is widely farmed in China and adult prawns can be infected by WSSV. However, the molecular mechanisms of the host pathogen interaction remain unknown. There is an urgent need to learn the host pathogen interaction between M. nipponense and WSSV which will be able to offer a solution in controlling the spread of WSSV. Next Generation Sequencing (NGS) was used in this study to determin the transcriptome differences by the comparison of control and WSSV-challenged moribund samples, control and WSSV-challenged survived samples of hepatopancreas in M. nipponense. A total of 64,049 predicted unigenes were obtained and classified into 63 functional groups. Approximately, 4,311 differential expression genes were identified with 3,308 genes were up-regulated when comparing the survived samples with the control. In the comparison of moribund samples with control, 1,960 differential expression genes were identified with 764 genes were up-regulated. In the contrast of two comparison libraries, 300 mutual DEGs with 95 up-regulated genes and 205 down-regulated genes. All the DEGs were performed GO and KEGG analysis, overall a total of 85 immune-related genes were obtained and these gene were groups into 13 functions and 4 KEGG pathways, such as protease inhibitors, heat shock proteins, oxidative stress, pathogen recognition immune receptors, PI3K/AKT/mTOR pathway, MAPK signaling pathway and Ubiquitin Proteasome Pathway. Ten genes that valuable in immune responses against WSSV were selected from those DEGs to furture discuss the response of host to WSSV. Results from this study contribute to a better understanding of the immune response of M. nipponense to WSSV, provide information for identifying novel genes in the absence of genome of M. nipponense. Furthermore, large number of transcripts obtained from this study could provide a strong basis for future genomic research on M. nipponense.

What vaccination studies tell us about immunological memory within the innate immune system of cultured shrimp and crayfish

The possibility of immunological memory in invertebrates is a topic that has recently attracted a lot of attention. Today, even vertebrates are known to exhibit innate immune responses that show memory-like properties, and since these responses are triggered by cells that are involved in the innate immune system, it seems that immune specificity and immune memory do not necessarily require the presence of B cells and T cells after all. This kind of immune response has been called "immune priming" or "trained immunity". In this report, we review recent observations and our current understanding of immunological memory within the innate immune system in cultured shrimp and crayfish after vaccination with live vaccine, killed vaccine and subunit vaccines. We also discuss the possible mechanisms involved in this immune response.

Ontogenetic changes in the expression of immune related genes in response to immunostimulants and resistance against white spot syndrome virus in Litopenaeus vannamei

In recent years, researchers have focused on viral and plant immunostimulants which could have beneficial effects in disease prevention and control in shrimp culture. At present, the application of the recombinant VP28 protein (r-VP28) and herbal immunostimulant has been considered as a more effective approach to prevent white spot syndrome (WSS) by enhancing the immune response in shrimp. In the present study, expression of selected immune related genes in response to r-VP28 and herbal immunostimulant mix (HIM) were separately studied qualitatively and quantitatively by RT-PCR and real time PCR, respectively during ontogenetic development from nauplius to juvenile stage in Litopenaeus vannamei. The mRNA expression level of immune related genes such as anti-lipopolysaccharides (ALF), Lysozyme, cMnSOD, Crustin, Prophenoloxidase, Tumor necrosis factor receptor-associated factor 6 (TRAF6) and Haemocyanin were found to be up-regulated significantly in different ontogenetic development stages of shrimp fed with r-VP28 and HIM formulated diets. Relative percent survival (RPS) was determined in shrimp fed with immunostimulants formulated diets after oral challenge with WSSV. The survival of WSSV challenged shrimp was found to be higher in immunostimulants treated groups when compared to untreated group. The results of PCR, ELISA and real time PCR revealed the absence of WSSV in WSSV-challenged shrimp after 20 days of treatment with immunostimulants. Among these immunostimulants, HIM was found to be more effective when compared to r-VP28. After a survey of literature, we are of the opinion that this might be the first report on the expression of immune genes during ontogenetic development of L. vannamei in response to immunostimulants.

Interleukin-8 holds promise to serve as a molecular adjuvant in DNA vaccination model against Streptococcus iniae infection in fish

DNA vaccines had been widely used in animal models against various viral infections, while it was not so convincing for many infectious diseases especially bacterial disease in aquaculture. Interleukin-8(IL-8) as one of the CXC chemokines, its immunological role and adjuvant potential which had been proved in mammals were rarely reported in fish species. In this study, recombination plasmid pcDNA3.1/IL-8(pcIL-8) was conducted and the capacity of IL-8 as molecular adjuvant was explored from several aspects by co-injecting with a DNA vaccine encoding α-enolase(pcENO) against Streptococcus iniae infection in channel catfish. The results suggested that co-injection of pcIL-8 with DNA vaccine increased the innate immunity and specific antibody levels, as well as increased the immune-related genes involving in pro-inflammatory response, humoral and cellular immunity. Moreover, pcIL-8 enhanced the immunoprotection of pcENO with the relative percent survival(RPS) of 60% to 80% against S.iniae infection at 4 week post vaccination(p.v.), with the significantly higher RPS of 73.33% in pcENO+pcIL-8 group compared with that of pcENO alone(53.33%) at challenge test of 8 weeks p.v. Taken together, these results indicate pcIL-8 as a molecular adjuvant co-injected with DNA vaccine not only improves the immunoprotection but also maintains long period of immunity for channel catfish against S.iniae infection. Our study signifies that IL-8 holds promise to serve as a potential adjuvant in DNA vaccines against bacterial infections for long time.

Effect of mixed-Bacillus spp isolated from pustulose ark Anadara tuberculosa on growth, survival, viral prevalence and immune-related gene expression in shrimp Litopenaeus vannamei

The widespread overuse of antibiotics in aquaculture has led to the emergence of antibiotic-resistance shrimp pathogens, the negative impact on shrimp gut microbiota, and the presence of antimicrobial residues in aquaculture products, with negative consequences on human health. Alternatively, probiotics have positive effects on immunological responses and productive performance of aquatic animals. In this study, three probiotic bacteria, (Bacillus licheniformis MAt32, B. subtilis MAt43 and B. subtilis subsp. subtilis GAtB1), isolated from the Anadara tuberculosa were included in diets for juvenile shrimp, Litopenaeus vannamei, to evaluate their effects on growth, survival, disease prevalence, and immune-related gene expression. Shrimp naturally infected with WSSV and IHHNV were fed with the basal diet (control, T1) and diets supplemented with four levels of bacilli probiotic mix (1:1:1) at final concentration of (T2) 1 × 10⁶, (T3) 2 × 10⁶, (T4) 4 × 10⁶, and (T5) 6 × 10⁶ CFU g^-1 of feed. The specific growth rate of shrimp was significantly higher in T2 than in T1 (control) treatment, and the final growth as well as the survival were similar among treated groups. The prevalence of WSSV and IHHNV infected shrimp was reduced in T2 and T4 treatments, respectively, compared with control. The mRNA expression of proPO gene was higher in treatment T4 than control. The LvToll1 gene was significantly up-regulated in treatments T4 and T5 compared to control. The SOD gene was up-regulated in treatment T5 compared to control. In contrast, the mRNA expression of the Hsp70 gene was down-regulated in treatments T4 and T5 respect to control, and the TGase gene remained unaffected by the level of bacillus probiotic mix. As conclusion, the bacilli probiotic mix (Bacillus spp.) enhanced immune-related gene expression in WSSV and IHHNV naturally infected shrimp. This is the first report of probiotic potential of bacteria isolated from A. tuberculosa on the immune response and viral prevalence in shrimp Litopenaeus vannamei.

The genome of the crustacean Parhyale hawaiensis, a model for animal development, regeneration, immunity and lignocellulose digestion

The amphipod crustacean Parhyale hawaiensis is a blossoming model system for studies of developmental mechanisms and more recently regeneration. We have sequenced the genome allowing annotation of all key signaling pathways, transcription factors, and non-coding RNAs that will enhance ongoing functional studies. Parhyale is a member of the Malacostraca clade, which includes crustacean food crop species. We analysed the immunity related genes of Parhyale as an important comparative system for these species, where immunity related aquaculture problems have increased as farming has intensified. We also find that Parhyale and other species within Multicrustacea contain the enzyme sets necessary to perform lignocellulose digestion ('wood eating'), suggesting this ability may predate the diversification of this lineage. Our data provide an essential resource for further development of Parhyale as an experimental model. The first malacostracan genome will underpin ongoing comparative work in food crop species and research investigating lignocellulose as an energy source.

DOI:http://dx.doi.org/10.7554/eLife.20062.001

The marine crustacean known as Parhyale hawaiensis is related to prawns, shrimps and crabs and is found at tropical coastlines around the world. This species has recently attracted scientific interest as a possible new model to study how animal embryos develop before birth and, because Parhyale can rapidly regrow lost limbs, how tissues and organs regenerate. Indeed, Parhyale has many characteristics that make it a good model organism, being small, fast-growing and easy to keep and care for in the laboratory.

Several research tools have already been developed to make it easier to study Parhyale. This includes the creation of a system for using the popular gene editing technology, CRISPR, in this animal. However, one critical resource that is available for most model organisms was missing; the complete sequence of all the genetic information of this crustacean, also known as its genome, was not available.

Kao, Lai, Stamataki et al. have now compiled the Parhyale genome – which is slightly larger than the human genome – and studied its genetics. Analysis revealed that Parhyale has genes that allow it to fully digest plant material. This is unusual because most animals that do this rely upon the help of bacteria. Kao, Lai, Stamataki et al. also identified genes that provide some of the first insights into the immune system of crustaceans, which protects these creatures from diseases.

Kao, Lai, Stamataki et al. have provided a resource and findings that could help to establish Parhyale as a popular model organism for studying several ideas in biology, including organ regeneration and embryonic development. Understanding how Parhyale digests plant matter, for example, could progress the biofuel industry towards efficient production of greener energy. Insights from its immune system could also be adapted to make farmed shrimp and prawns more resistant to infections, boosting seafood production.

DOI:http://dx.doi.org/10.7554/eLife.20062.002

The Pacific White Shrimp β-actin Promoter: Functional Properties and the Potential Application for Transduction System Using Recombinant Baculovirus

A newly isolated Pacific white shrimp (Litopenaeus vannamei) beta-actin promoter SbaP and its derivative compact construct SbaP (ENX) have recently been demonstrated to promote ectopic gene expression in vitro and in vivo. To further explore the potential transduction application, this newly isolated shrimp promoter SbaP was comparatively tested with cytomegalovirus (CMV), simian virus 40 (SV40), polyhedrin (Polh), and white spot syndrome virus immediate early gene 1 (WSSV ie1) four constitutive promoters and a beta-actin promoter (TbaP) from tilapia fish to characterize its promoting function in eight different cell lines. Luciferase quantitation assays revealed that SbaP can drive luciferase gene expression in all eight cell lines including sf21 (insect), PAC2 (zebrafish), EPC (carp), CHSE-214 (chinook salmon), GSTEF (green sea turtle), MS-1 (monk seal), 293T (human), and HeLa (human), but at different levels. Comparative analysis revealed that the promoting activity of SbaP was lower (≤10-fold) than CMV but higher (2-20 folds) than Polh in most of these cell lines tested. Whereas, SbaP mediated luciferase expression in sf21 cells was over 20-fold higher than CMV, SV40, Polh, and TbaP promoter. Compared to the SbaP, SbaP (ENX), which was constructed on the basis of SbaP by deletion of two "negative" regulatory elements, exhibited no significant change of promoting activity in EPC and PAC2 cells, but a 5 and 16 % lower promoting effect in 293T and HeLa cells, respectively. Additionally, a recombinant baculovirus was constructed under the control of SbaP (ENX), and efficient promoter activity of newly generated baculoviral vector was detected both in vitro of infected sf21 cells and in vivo of injected indicator shrimp. These results warrant the potential application of SbaP, particularly SbaP (ENX) in ectopic gene expression in future.

VP24 Is a Chitin-Binding Protein Involved in White Spot Syndrome Virus Infection

Oral ingestion is the major route of infection for the white spot syndrome virus (WSSV). However, the mechanism by which virus particles in the digestive tract invade host cells is unknown. In the present study, we demonstrate that WSSV virions can bind to chitin through one of the major envelope proteins (VP24). Mutagenesis analysis indicated that amino acids (aa) 186 to 200 in the C terminus of VP24 were required for chitin binding. Moreover, the P-VP24186-200 peptide derived from the VP24 chitin binding region significantly inhibited the VP24-chitin interaction and the WSSV-chitin interaction, implying that VP24 participates in WSSV binding to chitin. Oral inoculation experiments showed that P-VP24186-200 treatment reduced the number of virus particles remaining in the digestive tract during the early stage of infection and greatly hindered WSSV proliferation in shrimp. These data indicate that binding of WSSV to chitin through the viral envelope protein VP24 is essential for WSSV per os infection and provide new ideas for preventing WSSV infection in shrimp farms.

IMPORTANCE

In this study, we show that WSSV can bind to chitin through the envelope protein VP24. The chitin-binding domain of VP24 maps to amino acids 186 to 200 in the C terminus. Binding of WSSV to chitin through the viral envelope protein VP24 is essential for WSSV per os infection. These findings not only extend our knowledge of WSSV infection but also provide new insights into strategies to prevent WSSV infection in shrimp farms.

Design and Construction of Shrimp Antiviral DNA Vaccines Expressing Long and Short Hairpins for Protection by RNA Interference

DNA vaccines present the aquaculture industry with an effective and economically viable method of controlling viral pathogens that drastically affect productivity. Since specific immune response is rudimentary in invertebrates, the presence of RNA interference (RNAi) pathway in shrimps provides a promising new approach to vaccination. Plasmid DNA vaccines that express short or long double stranded RNA in vivo have shown protection against viral diseases. The design, construction and considerations for preparing such vaccines are discussed.

Effects of artificial infection of Litopenaeus vannamei by Micrococcus lysodeikticus and WSSV on the activity of immunity related enzymes

In this study, the activities of 5 immunity related enzymes namely acid phosphatase (ACP), alkaline phosphatase (AKP), phenoloxidase (PO), peroxidase (POD) and lysozyme phosphatase (LZM)) of Litopenaeus vannamei after they have been injected with different concentrations of Micrococcus lysodeikticus and the white spot syndrome virus (WSSV) were examined. The cumulative mortality at 0, 24, 48, 72, 96 h was obtained. Copy numbers of WSSV in L. vannamei after a single infection, secondary infection and concurrent infection were measured. Hemolymph samples of M. lysodeikticus and WSSV injected shrimp were collected at 0, 6, 12 24, 48, 72, 78, 84, 96 and 120 h. The results were: (i) The cumulative mortality of L. vannamei increased as the shrimp were infected with higher concentration of the bacteria; (ii) The most sensitive changes of ACP, AKP and LZM were in the 6.2 × 10(5), 6.2 × 10(6), 6.2 × 10(7) cfu/mL M. lysodeikticus group; (iii) ACP but LZM were more sensitive to M. lysodeikticus than WSSV, and AKP, PO and POD is more sensitive to WSSV; (iv) The copies of WSSV in the co-injected group were higher than WSSV-single infection and WSSV-bacteria-secondary infection group at 48 h. The amount of WSSV in L. vannamei of concurrent infection and WSSV-bacteria-secondary infection groups were higher than that of the WSSV-single infection group.

QTL for white spot syndrome virus resistance and the sex-determining locus in the Indian black tiger shrimp (Penaeus monodon)

Background

Shrimp culture is a fast growing aquaculture sector, but in recent years there has been a shift away from tiger shrimp Penaeus monodon to other species. This is largely due to the susceptibility of P. monodon to white spot syndrome virus disease (Whispovirus sp.) which has impacted production around the world. As female penaeid shrimp grow more rapidly than males, mono-sex production would be advantageous, however little is known about genes controlling or markers associated with sex determination in shrimp. In this study, a mapped set of 3959 transcribed single nucleotide polymorphisms were used to scan the P. monodon genome for loci associated with resistance to white-spot syndrome virus and sex in seven full-sibling tiger shrimp families challenged with white spot syndrome virus.

Results

Linkage groups 2, 3, 5, 6, 17, 18, 19, 22, 27 and 43 were found to contain quantitative trait loci significantly associated with hours of survival after white spot syndrome virus infection (P < 0.05 after Bonferroni correction). Nine QTL were significantly associated with hours of survival. Of the SNPs mapping to these and other regions with suggestive associations, many were found to occur in transcripts showing homology to genes with putative immune functions of interest, including genes affecting the action of the ubiquitin-proteasome pathway, lymphocyte-cell function, heat shock proteins, the TOLL pathway, protein kinase signal transduction pathways, mRNA binding proteins, lectins and genes affecting the development and differentiation of the immune system (eg. RUNT protein 1A). Several SNPs significantly associated with sex were mapped to linkage group 30, the strongest associations (P < 0.001 after Bonferroni correction) for 3 SNPs located in a 0.8 cM stretch between positions 43.5 and 44.3 cM where the feminisation gene (FEM-1, affecting sexual differentiation in Caenorhabditis elegans) mapped.

Conclusions

The markers for disease resistance and sexual differentiation identified by this study could be useful for marker assisted selection to improve resistance to WSSV and for identifying homogametic female individuals for mono-sex (all female) production. The genes with putative functions affecting immunity and sexual differentiation that were found to closely map to these loci provide leads about the mechanisms affecting these important economic traits in shrimp.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-731) contains supplementary material, which is available to authorized users.

Anti-viral gene induction is absent upon secondary challenge with double-stranded RNA in the Pacific oyster, Crassostrea gigas

Oyster farming is one of the most important aquaculture industries in the world. However, its productivity is increasingly limited by viral disease and we do not yet have management practices, such as protective vaccination, that can control these disease outbreaks. Hence, in the current study we investigated the expression of known anti-viral genes in oysters (Crassostrea gigas) in response to primary and secondary encounter with a virus associated molecular pattern (dsRNA), and tested whether a common form of epigenetic gene regulation (DNA methylation) was associated with the expression of these anti-viral genes. Injection of dsRNA into the adductor muscle resulted in the rapid and transient expression of virus recognition receptors (TLR & MDA5), whereas several anti-viral signalling (IRF & SOC-1) and effector (PKR & viperin) genes were still up-regulated at one week post primary challenge (p < 0.05). This primary encounter with dsRNA appeared to deplete the immune system because anti-viral gene induction was absent in the gills when oysters were given a second injection of dsRNA at 1-week post-primary injection. The expression of DNA methylation genes (DNMT1, DNMT3b, TDG, TET2) and DNA methylation profiles up-stream of specific anti-viral genes (STING, SOC-1 & Viperin) did not change in response to dsRNA injection (p > 0.05). These results collectively suggest that C. gigas does not have an enhanced anti-viral gene response (immune-priming) to secondary dsRNA challenge and that the sustained up-regulation of anti-viral signalling and effector genes following primary challenge is unlikely to be associated with upstream DNA methylation levels.

The promotion of cytoskeleton integration and redox in the haemocyte of shrimp Litopenaeus vannamei after the successive stimulation of recombinant VP28

VP28 protein has been reported to work as a "vaccine" to protect the host from white spot syndrome, but the detailed mechanism of vaccination with VP28 protein in shrimp is still far from well understood. In the present study, whole transcriptomes of shrimp haemocytes were sequenced using the SOLiD4 platform after the successive VP28 stimulation. Eight single-end fragment libraries were constructed and sequenced in the four groups including the VP28-VP28, PBS-VP28, PBS-PBS and BLANK group, and there were 243,949,667 single-end reads with length of 50bp obtained totally, with 14,800 genes further identified. After reads mapping and transcript assembling, 1027, 1539, 1158, 1091 and 1300 genes in five differentially expressed gene lists were obtained in the comparison of VP28-VP28 versus PBS-VP28, VP28-VP28 versus PBS-PBS, VP28-VP28 versus BLANK, PBS-VP28 versus PBS-PBS and PBS-VP28 versus BLANK, respectively. There were 555 differentially expressed genes responsive to the single VP28 stimulation after grouping the PBS-VP28_BLANK and PBS-VP28_PBS-PBS gene lists, and 269 ones responsive to the successive VP28 stimulation after grouping the VP28-VP28_BLANK, VP28-VP28_PBS-PBS and VP28-VP28_PBS-VP28 gene lists. In the GO enrichment analysis of the genes responsive to the single VP28 stimulation, five immune-related GO terms were observed among 14 increased terms, which included defense response to bacterium, response to stimulus, disruption of cells of other organism, killing of cells of other organism and response to bacterium. It was worth noting that the GO terms, response to stimulus and response to stress, were the most common annotation ones which accounted 28.7% and 18.8% of the total differently expressed genes, respectively. For the genes responsive to the successive VP28 stimulation, terms including actin filament-based movement and myosin heavy chain binding were mostly enriched in the Biological Process and Molecular Function category, respectively. In the Cellular Component category, the enriched GO terms were myosin VII complex, myosin V complex, myosin VI complex and myosin II complex. Furthermore, the most abundant GO term was oxidation-reduction process, followed by single-organism transport, neurogenesis and translation for 214 genes only responsive to successive VP28 stimulation. These results collectively indicated that the successive VP28 stimulation could modulate cytoskeleton integration and redox to promote the phagocytosis activity of shrimp haemocytes, which might protect effectively for shrimp against WSSV infection.

Protection of shrimp Penaeus monodon from WSSV infection using antisense constructs

White spot syndrome caused by white spot syndrome virus (WSSV) is one of the most threatening diseases of shrimp culture industry. Previous studies have successfully demonstrated the use of DNA- and RNA-based vaccines to protect WSSV infection in shrimp. In the present study, we have explored the protective efficacy of antisense constructs directed against WSSV proteins, VP24, and VP28, thymidylate synthase (TS), and ribonucleotide reductase-2 (RR2) under the control of endogenous shrimp histone-3 (H3) or penaedin (Pn) promoter. Several antisense constructs were generated by inserting VP24 (pH3-VP24, pPn-VP24), VP28 (pH3-VP28, pPn-VP28), TS (pH3-TS, pPn-TS), and RR2 (pH3-RR2) in antisense orientation. These constructs were tested for their protective potential in WSSV infected cell cultures, and their effect on reduction of the viral load was assessed. A robust reduction in WSSV copy number was observed upon transfection of antisense constructs in hemocyte cultures derived from Penaeus monodon and Scylla serrata. When tested in vivo, antisense constructs offered a strong protection in WSSV challenged P. monodon. Constructs expressing antisense VP24 and VP28 provided the best protection (up to 90 % survivability) with a corresponding decrease in the viral load. Our work demonstrates that shrimp treated with antisense constructs present an efficient control strategy for combating WSSV infection in shrimp aquaculture.

Characterization and interactome study of white spot syndrome virus envelope protein VP11

White spot syndrome virus (WSSV) is a large enveloped virus. The WSSV viral particle consists of three structural layers that surround its core DNA: an outer envelope, a tegument and a nucleocapsid. Here we characterize the WSSV structural protein VP11 (WSSV394, GenBank accession number AF440570), and use an interactome approach to analyze the possible associations between this protein and an array of other WSSV and host proteins. Temporal transcription analysis showed that vp11 is an early gene. Western blot hybridization of the intact viral particles and fractionation of the viral components, and immunoelectron microscopy showed that VP11 is an envelope protein. Membrane topology software predicted VP11 to be a type of transmembrane protein with a highly hydrophobic transmembrane domain at its N-terminal. Based on an immunofluorescence assay performed on VP11-transfected Sf9 cells and a trypsin digestion analysis of the virion, we conclude that, contrary to topology software prediction, the C-terminal of this protein is in fact inside the virion. Yeast two-hybrid screening combined with co-immunoprecipitation assays found that VP11 directly interacted with at least 12 other WSSV structural proteins as well as itself. An oligomerization assay further showed that VP11 could form dimers. VP11 is also the first reported WSSV structural protein to interact with the major nucleocapsid protein VP664.

DNA vaccines against viral diseases of farmed fish

Immunization by an antigen-encoding DNA was approved for commercial sale in Canada against a Novirhabdovirus infection in fish. DNA vaccines have been particularly successful against the Novirhabdoviruses while there are reports on the efficacy against viral pathogens like infectious pancreatic necrosis virus, infectious salmon anemia virus, and lymphocystis disease virus and these are inferior to what has been attained for the novirhabdoviruses. Most recently, DNA vaccination of Penaeus monodon against white spot syndrome virus was reported. Research efforts are now focused on the development of more effective vectors for DNA vaccines, improvement of vaccine efficacy against various viral diseases of fish for which there is currently no vaccines available and provision of co-expression of viral antigen and immunomodulatory compounds. Scientists are also in the process of developing new delivery methods. While a DNA vaccine has been approved for commercial use in farmed salmon in Canada, it is foreseen that it is still a long way to go before a DNA vaccine is approved for use in farmed fish in Europe.

Activation of an immune response in Litopenaeus vannamei by oral immunization with phagocytosis activating protein (PAP) DNA

The phagocytosis activating protein (PAP) gene has been reported to stimulate the phagocytic activity of shrimp hemocytes and to protect shrimp from several pathogens. In this study oral administration of the chitosan-PAP gene to shrimp was investigated for its ability to induce immunity. The PAP gene was cooperated into a phMGFP plasmid, named PAP-phMGFP. Chitosan-PAP-phMGFP nanoparticles were formed by mixing a low molecular weight chitosan (50 kDa) and a high molecular weight chitosan (150 kDa) with various ratios of PAP-phMGFP. The optimal ratio of chitosan PAP-phMGFP nanoparticles was first determined by transfection into Chinese Hamster Ovary (CHO) cells before being used for oral immunization in shrimp. The chitosan-PAP-phMGFP nanoparticles at a ratio of 2:1 with the low molecular weight chitosan were optimum for transfecting the CHO cells. The shrimp were then fed with 25, 50, 100 and 150 μg/shrimp/day of chitosan-PAP-phMGFP (2:1) nanoparticles then challenged by the white spot syndrome virus (WSSV). Shrimp fed with 50 μg of chitosan-PAP-phMGFP nanoparticles per day for 7 consecutive days, produced the highest relative percent survival (RPS) (94.45 ± 9.86%). The presence of PAP-phMGFP was detected in every shrimp tissue including the hemolymph, lymphoid organ, heart, hepatopancreas, intestine and muscle. The folds increase of the PAP gene expression increased significantly together with an increase of the phagocytic activity in the immunized shrimp. The stability of the PAP-phMGFP in the immunized shrimp hemolymph was detected by determination of the expression of the GFP at various days after immunization ceased. GFP expression was detected until the 15th day but not at the 30th day after immunization ceased. A quantitative analysis of the WSSV copies in shrimp heart tissue was significantly reduced in the immunized shrimp. In addition, chitosan-PAP-phMGFP nanoparticles protected shrimp against WSSV, Yellow head virus (YHV) and Vibrio harveyi with RPS values of 83.34 ± 7.86%, 55.56 ± 15.72% and 53.91 ± 5.52%, respectively. This study therefore confirms the role of the PAP gene in shrimp immunity and may lead to the development of a way to prevent microbial diseases of shrimp at an industrial level by appropriate feeding of a chitosan/DNA complex.

A vector that expresses VP28 of WSSV can protect red swamp crayfish from white spot disease

White spot disease caused by white spot syndrome virus (WSSV) leads to devastating losses in shrimp farming. The WSSV envelope protein VP28, can be used as subunit vaccines that can efficiently protect shrimp against WSSV disease. However, the function of the envelope protein VP19 was not confirmed, some researches found that VP19 could protect shrimp against WSSV, and other reports found it no any protection. To detect the functions of VP28 and VP19 and find a method to prevent this disease in red swamp crayfish Procambarus clarkii, we constructed the plasmid vectors pIevp28 and pIevp19, which contains the ie1 promoter and coding region of vp28 or vp19 of WSSV, respectively. The results of quantitative real-time PCR and western blot showed that the injected vectors could transcribe corresponding mRNAs and translate to the protein VP28 or VP19 in the crayfish. The vp28 or vp19 signal was detected on the third day post injection, and maintained its expression for 30days. The mortality of the crayfish with pIevp28 showed obvious decline compared with the controls (pIe and PBS injection). However, pIevp19 seems did not affect the mortality of the crayfish compared with the controls. Furthermore, only VP28 was found tightly bound to the host haemocytes under immunocytochemistry. The results suggest that the VP28 protein might protect shrimp from the virus through competitive inhibition. We also found that oral administration of Escherichia coli with pIevp28 could protect crayfish from white spot disease, but the E. coli with pIevp19 was not. Therefore, we think that oral administration of bacteria with pIevp28 is a potentially easy therapeutic way against white spot disease in aquaculture.

A second copper zinc superoxide dismutase (CuZnSOD) in the blue crab Callinectes sapidus: cloning and up-regulated expression in the hemocytes after immune challenge

The full-length cDNA (1362 nucleotides, GenBank JF736621) encoding an extracellular copper zinc superoxide dismutase initially isolated from an EST library of the blue crab Callinectes sapidus was characterized using 3' RACE and named Cas-ecCuZnSOD-2. The open reading frame of Cas-ecCuZnSOD-2 contains 203 deduced amino acids with the conserved active catalytic center for copper and zinc binding and the post-translational modification at two putative N-glycosylation and nine phosphorylation sites. Overall, the deduced amino acids of Cas-ecCuZnSOD-2 shared only 35% sequence identity with that of Cas-ecCuZnSOD (GenBank AF264031) which was previously found in C. sapidus, while it showed ∼75% sequence identity to Scylla paramamosain ecCuZnSOD (GenBank FJ774661). The expression profile of Cas-ecCuZnSOD-2 and the other three C. sapidus SODs: ecCuZn, cytMn- and mitMn SODs was largely ubiquitous among the tested tissues obtained from a juvenile female at intermolt: brain, eyestalk ganglia, pericardial organs, and thoracic ganglia complex (nervous system); hepatopancreas (digestive system); heart, artery and hemocytes (circulatory system); gill and antennal gland (excretory system), hypodermis, and Y-organ (endocrine organ). Our study reports, for the first time in the crustaceans, expression analyses for all four Cas-SODs in hemocytes after immune challenges. Crabs challenged with lipopolysaccharides (LPS) injection had a remarkable induction of Cas-ecCuZnSOD-2 expression along with three other SODs in hemocytes, suggesting that Cas-SODs including Cas-ecCuZnSOD-2 are involved in the defense system, possibly innate immunity and immunocompetency of C. sapidus.

Histological alterations and immune response in the crayfish Procambarus clarkii given rVP28-incorporated diets

There is growing evidence that recombinant VP28 protein (rVP28) can significantly enhance immune response and disease resistance against white spot syndrome virus (WSSV) in shrimp, although the underlying mechanisms have not been entirely clarified yet. The aim of this study was to determine the effect of rVP28 on histological alterations and WSSV-induced apoptosis in crayfish Procambarus clarkii. Crayfish were fed commercial diets supplemented with different doses of HyNPV-VP28 infected pupae (rVP28-hp) for 4 weeks. Results showed that rVP28-hp may be used as a safe and effective source of medicinal proteins in aquaculture when supplemented in diet at low dose (10 g kg(-1) and 50 g kg(-1)), which could obviously reduce the percentage of apoptotic cells in stomach, gut and hepatopancreas tissues induced by the WSSV challenge and showed the relative percent survival (RPS) of 82.2% and 94.4%, respectively. But rVP28-hp would be detrimental to crayfish survival and decrease resistance to WSSV infection at the high dose (100 g kg(-1) and 200 g kg(-1)), with the cumulative mortality of up to 48.2% and 56.6% after WSSV challenge, respectively. During a 28-d feeding period, the survival rate of crayfish was only 54.5%-75.6%, and histopathological observation showed that one of the principal lesions was serious cell swelling, vacuolar degeneration and necrosis in hepatopancreatic epithelia and myocardial cells. These results suggested that rVP28-hp can influence the immune functions of crayfish in a dose-dependent manner, and the rVP28-hp at the dose of 50 g kg(-1) was recommended to prevent WSSV in crayfish culture.

Surface-displayed VP28 on Bacillus subtilis spores induce protection against white spot syndrome virus in crayfish by oral administration

AIM

Surface-displayed heterologous antigens on Bacillus subtilis spores can induce the vertebrate animals tested to generate local and systematic immune response through oral immunization. Here, the protection potential of the recombinant spores displaying the VP28 protein of white spot syndrome virus (WSSV) was investigated in the invertebrate crayfish (Cambarus clarkii).

METHODS AND RESULTS

The VP28 protein was successfully displayed on the surfaces of B. subtilis spores using CotB or CotC as a fusion partner. Crayfish were administrated orally by feeding the feed pellets coated with B. subtilis spores for 7 days and immediately followed by WSSV challenge. Oral administration of either spores expressing CotB-VP28 or CotC-VP28 resulted in significantly higher relative survival rates of 37.9 and 44.8% compared with the crayfish orally administrated with the spores nonexpressing VP28 (10.3% relative survival rate). When challenges were separately conducted at 7 and 21 days after oral administration, the relative survival rates increased to 46.4 and 50% at 7 days post-oral administration, but decreased to 30 and 33.3% at 21 days after oral administration.

CONCLUSION

These evidences indicate that the surface-displayed VP28 on B. subtilis spore could induce protection of crayfish against WSSV via oral administration.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report to use the spore surface display system to deliver orally a heterologous antigen in an aquatic invertebrate animal, crayfish. The results presented here suggest that the spore-displayed VP28 might be suitable for an oral booster vaccine on prevention of WSSV infection in shrimp farming.

Stimulating the immune response of Litopenaeus vannamei using the phagocytosis activating protein (PAP) gene

High mortality in the shrimp farming industry is caused by several pathogens such as white spot syndrome virus (WSSV), yellow head virus (YHV) and Vibrio harveyi (V. harveyi). A PAP (Phagocytosis activating protein) gene able to activate phagocytosis of shrimp hemocytes was cloned into the eukaryotic expression vector phMGFP. In vitro expression was confirmed by transfection of PAP-phMGFP into CHO (Chinese Hamster Ovary) cells and the expression of the Green Fluorescent Protein (GFP) was observed. In order to activate the phagocytic activity of shrimp, 20, 40 and 80 μg/shrimp of this PAP-phMGFP vector were injected into Litopenaeus vannamei muscle. After challenged with WSSV, 40 μg/shrimp produced the highest relative percent survival (77.78 RPS). Analysis for the expression of the GFP gene in various tissues showed the expression mostly in the hemolymph of the immunized shrimp. The expression level of PAP and proPO (Prophenoloxidase) gene were highest at 7 days after immunization. This agreed with the efficiency of protection against WSSV that also occurred 7 days after immunization with the highest RPS of 86.61%. However there was no protection 30 days after immunization. Hemocytes of shrimp injected with PAP-phMGFP had 1.9 folds and 3 folds higher percentage phagocytosis and phagocytic index than the shrimp injected with PBS. Accordingly, copies of WSSV reduced in the PAP-phMGFP injected shrimp. In addition, PAP-phMGFP also protected shrimp against several pathogens: WSSV, YHV and V. harveyi, with RPS values of 86.61%, 63.34% and 50% respectively. This finding shows that the immune cellular defense mechanisms in shrimp against pathogens can be activated by injection of PAP-phMGFP and could indicate possible useful ways to begin to control this process.

Transcriptional regulation of extracellular copper zinc superoxide dismutase from white shrimp Litopenaeus vannamei following Vibrio alginolyticus and WSSV infection

The cDNA encoding an extracellular copper zinc superoxide dismutase (LvECSOD) was cloned from the hepatopancreas of white shrimp Litopenaeus vannamei. It consisted of 915 bp nucleotides with an open reading frame corresponding to a deduced protein of 178 amino acids. The LvECSOD contains a putative signal peptide of 16 amino acids, two potential N-linked glycosylation sites (N(115)GTA and N(135)ITG) and a copper zinc superoxide dismutase family signature sequence (G(162)NAGaRvACctI(173)). It was found that four copper binding sites, four zinc binding sites and two cysteines involving in the formation of the disulfide bridge were conserved in the protein. LvECSOD shared 33-58% identity to ECSODs from other organisms. Expression analysis revealed that LvECSOD mRNA was widely distributed in all the tissues examined. When the shrimp challenged with Vibrio alginolyticus or white spot syndrome virus (WSSV), expression of LvECSOD mRNA in the hepatopancreas and hemocytes was mediated responsively. Our results suggested that LvECSOD was implicated in the immune response induced by V. alginolyticus and WSSV.

A 3D model of the membrane protein complex formed by the white spot syndrome virus structural proteins

BACKGROUND

Outbreaks of white spot disease have had a large negative economic impact on cultured shrimp worldwide. However, the pathogenesis of the causative virus, WSSV (whit spot syndrome virus), is not yet well understood. WSSV is a large enveloped virus. The WSSV virion has three structural layers surrounding its core DNA: an outer envelope, a tegument and a nucleocapsid. In this study, we investigated the protein-protein interactions of the major WSSV structural proteins, including several envelope and tegument proteins that are known to be involved in the infection process.

PRINCIPAL FINDINGS

In the present report, we used coimmunoprecipitation and yeast two-hybrid assays to elucidate and/or confirm all the interactions that occur among the WSSV structural (envelope and tegument) proteins VP51A, VP19, VP24, VP26 and VP28. We found that VP51A interacted directly not only with VP26 but also with VP19 and VP24. VP51A, VP19 and VP24 were also shown to have an affinity for self-interaction. Chemical cross-linking assays showed that these three self-interacting proteins could occur as dimers.

CONCLUSIONS

From our present results in conjunction with other previously established interactions we construct a 3D model in which VP24 acts as a core protein that directly associates with VP26, VP28, VP38A, VP51A and WSV010 to form a membrane-associated protein complex. VP19 and VP37 are attached to this complex via association with VP51A and VP28, respectively. Through the VP26-VP51C interaction this envelope complex is anchored to the nucleocapsid, which is made of layers of rings formed by VP664. A 3D model of the nucleocapsid and the surrounding outer membrane is presented.

Protection of blue shrimp (Litopenaeus stylirostris) against the White Spot Syndrome Virus (WSSV) when injected with shrimp lysozyme

In this study we found that a blue shrimp (Litopenaeus stylirostris) lysozyme gene (Lslzm) was up-regulated in WSSV-infected shrimp, suggesting that lysozyme is involved in the innate response of shrimp to this virus. Shrimp were intramuscularly injected with Lslzm protein to identify how this recombinant protein protects L. stylirostris from WSSV infection and to determine how this protein influences nonspecific cellular and humoral defense mechanisms. Higher survival rates and a lower viral load (compared with controls) were reported for shrimps that were first injected with the Lslzm protein and then infected with WSSV. In addition, the Lslzm expression level and the immunological parameters (including THC, phagocytic activity, respiratory burst activity, phenoloxidase activity and lysozyme activity) were all significantly higher in the WSSV-infected shrimp treated with the Lslzm protein, compared with the controls. These results indicate that lysozyme is effective at blocking WSSV infection in L. stylirostris and that lysozyme modulates the cellular and humoral defense mechanisms after they are suppressed by the WSSV virus.

White spot syndrome virus: an overview on an emergent concern

Viruses are ubiquitous and extremely abundant in the marine environment. One of such marine viruses, the white spot syndrome virus (WSSV), has emerged globally as one of the most prevalent, widespread and lethal for shrimp populations. However, at present there is no treatment available to interfere with the unrestrained occurrence and spread of the disease. The recent progress in molecular biology techniques has made it possible to obtain information on the factors, mechanisms and strategies used by this virus to infect and replicate in susceptible host cells. Yet, further research is still required to fully understand the basic nature of WSSV, its exact life cycle and mode of infection. This information will expand our knowledge and may contribute to developing effective prophylactic or therapeutic measures. This review provides a state-of-the-art overview of the topic, and emphasizes the current progress and future direction for the development of WSSV control strategies.