Characterization of an immune deficiency homolog (IMD) in shrimp (Fenneropenaeus chinensis) and crayfish (Procambarus clarkii)

Characterization of a novel immune deficiency gene of Macrobrachium rosenbergii reveals antibacterial and antiviral defenses

OBJECTIVE

We sought to identify and characterize an immune deficiency (IMD) homolog from the giant freshwater prawn (also known as the giant river prawn) Macrobrachium rosenbergii. The IMD is a death-domain-containing protein that plays a crucial role as an adaptor protein in the IMD pathway-one of the most important response mechanisms to viral and bacterial invasion of invertebrates.

METHODS

An IMD homolog gene from M. rosenbergii (MrIMD) was isolated using rapid amplification of complementary DNA ends. The tissue distribution and response to immune challenge of MrIMD were analyzed by real-time reverse transcription polymerase chain reaction to understand the regulatory mechanism of MrIMD messenger RNA (mRNA) expression in M. rosenbergii.

RESULT

The open reading frame of MrIMD comprised 555 nucleotides encoding a protein consisting of 184 amino acids, with a conserved death domain at the C-terminus. The MrIMD protein demonstrated 53-74% similarity with IMDs from other crustaceans; the highest similarity was with the IMD from the oriental river prawn M. nipponense. Gene expression analysis revealed that MrIMD mRNA levels were highest in gill tissues. After Aeromonas hydrophila stimulation, MrIMD was significantly upregulated in the muscle, gills, and intestine, whereas there was no significant difference in the hemocytes and hepatopancreas. In the case of Macrobrachium rosenbergii nodavirus stimulation, MrIMD was dramatically upregulated in the muscle and hepatopancreas, whereas downregulation was observed in the gills.

CONCLUSION

These results suggest that the MrIMD gene may play different roles in response to gram-negative bacteria and viral infection and plays a crucial role in innate immunity as an important key molecule in the defense against bacterial and viral infections.

Insights into molecular aspects of pathogenesis and disease management in acute hepatopancreatic necrosis disease (AHPND): An updated review

Shrimp aquaculture is a rapidly growing sector that makes a significant economic contribution. However, the aquaculture industry is confronted with significant challenges, and infectious diseases, notably Acute Hepatopancreatic Necrosis Disease (AHPND), have emerged as severe threat. AHPND is caused by pathogens carrying the pVA-1 plasmid, which expresses the PirAB toxin, and it has wreaked havoc in shrimp aquaculture, imposing substantial economic burdens. To address this issue, it is crucial to delve into shrimp's immune responses. Therefore, this comprehensive review offers an in-depth examination of AHPND outbreaks, encompassing various facets such as environmental factors, host susceptibility, and the mechanisms employed by the pathogens. Traditional approaches to combat AHPND, primarily relying on chemicals and antibiotics, have raised concerns related to antibiotic resistance and have demonstrated limited success in disease control. Hence this review spotlights recent advancements in molecular diagnostics, therapeutic agents, and research related to shrimp immunity. Understanding these developments is crucial in the ongoing battle against AHPND. In conclusion, this review underscores the pressing need to comprehend the underlying mechanisms of AHPND pathogenesis and emphasizes the importance of developing comprehensive and effective solutions to combat this devastating disease, which continues to threaten the sustainability of shrimp farming.

Transcriptome analysis of Macrobrachium rosenbergii hemocytes in response to Staphylococcus aureus infection

The aquaculture industry has suffered significant financial losses as a result of disease outbreaks. In particular, disease outbreaks have become a major problem that can seriously affect the sustainable development of the Macrobrachium rosenbergii aquaculture industry. It is crucial to determine the defense mechanism of the host after pathogenic invasion in order to provide effective defense measures after disease outbreaks. Shrimp, like other invertebrates, primarily depend on their innate immune systems to defend against pathogens, and recognize and resist pathogens through humoral and cellular immune responses. In this investigation, we used RNA-seq technology to investigate the transcriptome of hemocytes from M. rosenbergii induced by Staphylococcus aureus. Our main targets were immune pathways and genes related to innate immunity. RNA-seq identified 209,069 and 204,775 unigenes in the control and experimental groups, respectively. In addition, we identified 547 and 1734 differentially expressed genes (DEGs) following S. aureus challenge after 6 and 12 h (h), respectively. GO and KEGG enrichment analysis revealed that the DEGs were significantly enriched in several biological signalling pathways, including NOD-like receptor, PI3K-Akt, Toll and Imd, IL-17, TGF-beta, RIG-I-like receptor, cAMP, apoptosis, and C-type lectin receptor. Sixteen DEGs were chosen at random for qPCR verification; these results concurred with those from sequencing. Our findings revealed that immune-related genes play an important role in antibacterial activities and have specific functions for gram-positive bacteria. These results provide more data for the prevention of M. rosenbergii diseases and offer a basis for the better prevention of diseases.

Scavenger receptor B2, a type III membrane pattern recognition receptor, senses LPS and activates the IMD pathway in crustaceans

The immune deficiency (IMD) pathway is critical for elevating host immunity in both insects and crustaceans. The IMD pathway activation in insects is mediated by peptidoglycan recognition proteins, which do not exist in crustaceans, suggesting a previously unidentified mechanism involved in crustacean IMD pathway activation. In this study, we identified a Marsupenaeus japonicus B class type III scavenger receptor, SRB2, as a receptor for activation of the IMD pathway. SRB2 is up-regulated upon bacterial challenge, while its depletion exacerbates bacterial proliferation and shrimp mortality via abolishing the expression of antimicrobial peptides. The extracellular domain of SRB2 recognizes bacterial lipopolysaccharide (LPS), while its C-terminal intracellular region containing a cryptic RHIM-like motif interacts with IMD, and activates the pathway by promoting nuclear translocation of RELISH. Overexpressing shrimp SRB2 in Drosophila melanogaster S2 cells potentiates LPS-induced IMD pathway activation and diptericin expression. These results unveil a previously unrecognized SRB2-IMD axis responsible for antimicrobial peptide induction and restriction of bacterial infection in crustaceans and provide evidence of biological diversity of IMD signaling in animals. A better understanding of the innate immunity of crustaceans will permit the optimization of prevention and treatment strategies against the arising shrimp diseases.

Transcriptome analysis of Macrobrachium rosenbergii hemocytes reveals in-depth insights into the immune response to Vibrio parahaemolyticus infection

Macrobrachium rosenbergii as one of the common freshwater prawn species in Southeast Asia, which breeding industry is seriously threatened by vibriosis and causes high mortality. In this study, the RNA-seq was employed for assessing the M. rosenbergii hemocytes transcriptomes following Vibrio parahaemolyticus challenge. After challenge for 6 h (h), there were overall 1849 DEGs or differentially expressed genes, including 1542 up-regulated and 307 down-regulated genes, and there was a total of 1048 DEGs, including 510 up-regulated genes and 538 down-regulated genes, after challenge for 12 h. Mitogen-activated protein kinase (MAPK) immune-related pathways, Toll, immune deficiency (IMD), and Janus kinase (JAK)/signal transducer and activator of transcription (STAT) were among the immune pathways where a lot of the DEGs were connected. The expression patterns of 18 chosen immune-related genes were examined utilizing qRT-PCR or quantitative real-time polymerase chain reaction, which revealed that the V. parahaemolyticus infection activated the M. rosenbergii's immune response. Permutational multivariate analysis of variance (PERMANOVA) showed that V. parahaemolyticus infection modulated immune regulation and apoptosis pathways. The gathered information provided new insight into M. rosenbergii's immunity and suggested a novel approach to fight against bacterial infection.

White spot syndrome virus impact on the expression of immune genes and gut microbiome of black tiger shrimp Penaeus monodon

The gut microbiome plays an essential role in the immune system of invertebrates and vertebrates. Pre and pro-biotics could enhance the shrimp immune system by increasing the phenoloxidase (PO), prophenoloxidase (ProPO), and superoxide dismutase activities. During viral infection, the host immune system alteration could influence the gut microbiome composition and probably lead to other pathogenic infections. Since the JAK/STAT pathway is involved in white spot syndrome virus (WSSV) infection, we investigated the intestine immune genes of STAT-silenced shrimp. During WSSV infection, expression levels of PmVago1, PmDoral, and PmSpätzle in PmSTAT-silenced shrimp were higher than normal. In addition, the transcription levels of antimicrobial peptides, including crustinPm1, crustinPm7, and PmPEN3, were higher in WSSV-challenged PmSTAT-silenced shrimp than the WSSV-infected normal shrimp. Meanwhile, PmSTAT silencing suppressed PmProPO1, PmProPO2, and PmPPAE1 expressions during WSSV infection. The microbiota from four shrimp tested groups (control group, WSSV-infected, PmSTAT-silenced, and PmSTAT-silenced infected by WSSV) was significantly different, with decreasing richness and diversity due to WSSV infection. The relative abundance of Bacteroidetes, Actinobacteria, and Planctomycetes was reduced in WSSV-challenged shrimp. However, at the species level, P. damselae, a pathogen to human and marine animals, significantly increased in WSSV-challenged shrimp. In constrast, Shewanella algae, a shrimp probiotic, was decreased in WSSV groups. In addition, the microbiota structure between control and PmSTAT-silenced shrimp was significantly different, suggesting the importance of STAT to maintain the homeostasis interaction with the microbiota.

Effects of the Clostridium butyricum on growth performance, antioxidant capacity, immunity and disease resistance of Litopenaeus Vannamei fed with cottonseed protein concentrate (CPC) replacement of fishmeal in diet

Clostridium butyricum (CB) is a gram-positive bacterium that secretes short-chain fatty acids such as butyric acid and so on. An 8-week feeding trial was conducted to investigate the effects of CB on the growth performance, antioxidant capacity, immunity and resistance to Vibrio parahaemolyticus in Litopenaeus Vannamei fed with cottonseed protein concentrate (CPC) replacement of fishmeal. Six iso-nitrogenous (40%) and iso-lipidic (6%) diets were formulated including a positive control group (PC, 25% fishmeal), a negative control group (NC, CPC replaced 30% of fishmeal protein), and 0.03% (C1, 3 × 10⁸ CFU/kg), 0.12% (C2, 1.2 × 10⁹ CFU/kg), 0.48% (C3, 4.8 × 10⁹ CFU/kg) and 1.92% (C4, 1.92 × 10¹⁰ CFU/kg) CB were supplemented on the negative control group (NC). After the feeding trial, the remaining shrimp in each treatment group were subjected to a challenge experiment with Vibrio parahaemolyticus. The results indicated that weight gain rate (WGR), specific growth rate (SGR) in C4 group were significantly lower than those in PC and C2 groups (P < 0.05); the feed conversion ratio (FCR) was significantly higher than that of PC and C2 groups (P < 0.05). There was no significant difference in survival rate (SR) among all groups (P > 0.05). Compared to the PC and NC groups, the total superoxide capacity, superoxide dismutase and lysozyme were significantly higher in the C4 group (P < 0.05); the glutathione peroxidase, acid phosphatase and alkaline phosphatase were significantly higher in the C3 group (P < 0.05); and the malondialdehyde was significantly lower in the C4 group (P < 0.05). The relative mRNA expressions of Toll receptor (TLR), innate immune deficiency gene (IMD), penaiedin3a (Pen3) were significantly down-regulated in the NC group than those in the PC group (P < 0.05). In addition, the relative mRNA expressions of TLR, IMD and Pen3 were significantly up-regulated in all groups supplemented with CB than those in the NC group (P < 0.05). Moreover, the cumulative mortality rate in the NC group was not significantly different from the PC group (P > 0.05) and was significantly higher than those in the C3 and C4 groups (P < 0.05). In conclusion, the CB supplementation on the basis of CPC replacement of 30% fishmeal protein enhanced significantly the antioxidant capacity, immunity and disease resistance of shrimp and improved its growth performance. Therefore, considering the factors of the growth, immunity and disease resistance, the CB supplementation of 0.12%-0.48% (1.2 × 10⁹ CFU/kg-4.8 × 10⁹ CFU/kg) was recommended in the diet of L. vannamei based on the results of this experiment.

Identification and function analysis of an immune deficiency homolog in swimming crab, Portunus trituberculatus

The immune deficiency (IMD) pathway is involved in both antiviral and antibacterial immune responses in Drosophila. IMD protein is the key adaptor to link the extracellular signal and the intracellular reaction to initiate the signal transduction in IMD pathway. In present study, the cDNA of the IMD (Pt-IMD) was identified from a marine crab, Portunus trituberculatus. The Pt-IMD is predicted to encode 170 amino acids with a death domain. Real-Time quantitative PCR analysis showed that Pt-IMD was constitutively expressed in hemocytes, intestine, gill, heart, muscle and hepatopancreas in normal crab. Moreover, the transcript of Pt-IMD in large-granule hemocytes is approximately 6-fold higher than semi-granular cells and agranular cells. Intracellular localization showed Pt-IMD was distributed mainly in the cytoplasm when it was over-expressed in Drosophila Schneider 2 (S2) cell. Functionally, over-expression of Pt-IMD could activate the promoters of Drosophila antimicrobial peptide genes (AMPs) in S2 cell. Furthermore, Pt-IMD expression was also knock-down by RNAi to determine the function of Pt-IMD on regulation of the expression of different antimicrobial peptides (AMPs) in crab. In the primary cultured hemocytes challenged with or without Vibrio alginolyticus, after Pt-IMD was knocked-down by specific long double strand RNA, the expression of anti-lipopolysaccharide factor1 (ALF1), ALF3, crustin1, crustin3, arasin2, hyastatin1and hyastatin3 have been significantly inhibited in normal cell or bacterial infected cell, while the expression of lysozyme was normal in non-infected cells and was significantly induced in bacterial infected cells, which compared to the non-specific dsRNA treated cells.

The potential of antimicrobial peptides isolated from freshwater crayfish species in new drug development: A review

The much-publicised increased resistance of pathogenic bacteria to conventional antibiotics has focused research effort on the characterization of new antimicrobial drugs. In this context, antimicrobial peptides (AMPs) extracted from animals are considered a promising alternative to conventional antibiotics. In recent years, freshwater crayfish species have emerged as an important source of bioactive compounds. In fact, these invertebrates rely on an innate immune system based on cellular responses and on the production of important effectors in the haemolymph, such as AMPs, which are produced and stored in granules in haemocytes and released after stimulation. These effectors are active against both Gram-positive and Gram-negative bacteria. In this review, we summarise the recent progress on AMPs isolated from the several species of freshwater crayfish and their prospects for future pharmaceutical applications to combat infectious agents.

PmAP2-β depletion enhanced activation of the Toll signaling pathway during yellow head virus infection in the black tiger shrimp Penaeus monodon

Yellow head virus (YHV) is a pathogen which causes high mortality in penaeid shrimp. Previous studies suggested that YHV enters shrimp cells via clathrin-mediated endocytosis. This research investigated the roles of clathrin adaptor protein 2 subunit β (AP-2β) from Penaeus monodon during YHV infection. PmAP2-β was continuously up-regulated more than twofold during 6–36 hpi. Suppression of PmAP2-β significantly reduced YHV copy numbers and delayed shrimp mortality. Quantitative RT-PCR revealed that knockdown of PmAP2-β significantly enhanced the expression level of PmSpätzle, a signaling ligand in the Toll pathway, by 30-fold at 6 and 12 hpi. Moreover, the expression levels of gene components in the Imd and JAK/STAT signaling pathways under the suppression of PmAP2-β during YHV infection were also investigated. Interestingly, anti-lipopolysaccharide factor isoform 3 (ALFPm3) was up-regulated by 40-fold in PmAP2-β knockdown shrimp upon YHV infection. In addition, silencing of PmAP2-β dramatically enhanced crustinPm1 expression in YHV-infected shrimp. Knockdown of ALFPm3 and crustinPm1 significantly reduced shrimp survival rate. Taken together, this work suggested that PmAP2-β-deficiency promoted the Toll pathway signalings, resulting in elevated levels of ALFPm3 and crustinPm1, the crucial antimicrobial peptides in defence against YHV.

A Comprehensive Review on Crustaceans' Immune System With a Focus on Freshwater Crayfish in Relation to Crayfish Plague Disease

Freshwater crayfish immunity has received great attention due to the need for urgent conservation. This concern has increased the understanding of the cellular and humoral defense systems, although the regulatory mechanisms involved in these processes need updating. There are, however, aspects of the immune response that require clarification and integration. The particular issues addressed in this review include an overall description of the oomycete Aphanomyces astaci, the causative agent of the pandemic plague disease, which affects freshwater crayfish, and an overview of crustaceans' immunity with a focus on freshwater crayfish. It includes a classification system of hemocyte sub-types, the molecular factors involved in hematopoiesis and the differential role of the hemocyte subpopulations in cell-mediated responses, including hemocyte infiltration, inflammation, encapsulation and the link with the extracellular trap cell death pathway (ETosis). In addition, other topics discussed include the identity and functions of hyaline cells, the generation of neoplasia, and the emerging topic of the role of sessile hemocytes in peripheral immunity. Finally, attention is paid to the molecular execution of the immune response, from recognition by the pattern recognition receptors (PRRs), the role of the signaling network in propagating and maintaining the immune signals, to the effector elements such as the putative function of the Down syndrome adhesion molecules (Dscam) in innate immune memory.

Planarians (Platyhelminthes)-An Emerging Model Organism for Investigating Innate Immune Mechanisms

An organism responds to the invading pathogens such as bacteria, viruses, protozoans, and fungi by engaging innate and adaptive immune system, which functions by activating various signal transduction pathways. As invertebrate organisms (such as sponges, worms, cnidarians, molluscs, crustaceans, insects, and echinoderms) are devoid of an adaptive immune system, and their defense mechanisms solely rely on innate immune system components. Investigating the immune response in such organisms helps to elucidate the immune mechanisms that vertebrates have inherited or evolved from invertebrates. Planarians are non-parasitic invertebrates from the phylum Platyhelminthes and are being investigated for several decades for understanding the whole-body regeneration process. However, recent findings have emerged planarians as a useful model for studying innate immunity as they are resistant to a broad spectrum of bacteria. This review intends to highlight the research findings on various antimicrobial resistance genes, signaling pathways involved in innate immune recognition, immune-related memory and immune cells in planarian flatworms.

Differential transcriptomic analysis of crayfish (Procambarus clarkii) from a rice coculture system challenged by Vibrio parahaemolyticus

Rice-crayfish (Procambarus clarkii) coculture is an effective farming mode and has been promoted in various regions of China. However, infection in crayfish can be a significant economic drain. We found crayfish infected with Vibrio parahemolyticus (VP), and to understand the molecular mechanisms of the immune responses of crayfish to VP infection, Illumina sequencing was employed to identify changes in the mRNA of hepatopancreatic tissue. A total of 47.30 and 43.01million high-quality transcriptome reads were generated from the hepatopancreatic samples of the experimental group (EG) and control group (CG), respectively. We found 5559 genes were significantly differentially expressed, including 2521 up-regulated genes (45.35%) and 3038 down-regulated genes (54.65%). These genes were enriched in 126 GO terms and 76 KEGG pathways (P ≤ 0.05), including the MAPK and PI3K-Akt signaling pathways and cell adhesion molecules, with 23 up-regulated genes and 3 down-regulated genes related to immune responses in the EG relative to the CG. Histopathological analysis revealed that the epithelial cells of the hepatopancreatic tubules in the EG were severely atrophic, necrotic, and exfoliated, resulting in thin and collapsing hepatopancreatic tubules. The expression patterns of 8 differentially expressed genes involved in immune responses were validated by quantitative real-time RT-PCR. These results provide a valuable basis for the immune responses of crayfish to acute hepatopancreatic necrosis disease at transcriptome level.

Research progress in innate immunity of freshwater crustaceans

Invertebrates lack adaptive immunity and innate immunity plays important roles in combating foreign invasive pathogens. Freshwater crustaceans, which are invertebrates, depend completely on their innate immune system. In recent years, many immune-related molecules in freshwater crustaceans, as well as their functions, have been identified. Three main immune signaling pathways, namely, Toll, immune deficiency (IMD), and Janus kinase-signal transducer activator of transcription (JAK/STAT) pathways, were found in freshwater crustaceans. A series of pattern recognition receptors (PRRs), including Toll receptors, lectins, lipopolysaccharide and β-1,3-glucan binding protein, scavenger receptors, Down syndrome cell adhesion molecules, and thioester-containing proteins, were reported. Prophenoloxidase activation system and antimicrobial peptide synthesis are two important immune effector systems. These components are involved in the innate immunity of freshwater crustaceans, and they function in the innate immune defense against invading pathogens. This review mainly summarizes innate immune signaling pathways, PRRs, and effector molecules in freshwater crustaceans.

The Anti-lipopolysaccharide Factors in Crustaceans

Anti-lipopolysaccharide factors (ALFs) are a type of antimicrobial peptide (AMP) which show broad-spectrum antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria, fungi and viruses. In this chapter, we review the discovery and classification of this kind of antimicrobial peptide in crustaceans. The structure and function, as well as the mechanism of antibacterial and antiviral activities of ALFs will be summarized and discussed. We will then describe the expression and regulation of various ALF genes in different crustacean species. Finally, the application prospects of ALFs in drug development and disease-resistant genetic breeding will be pointed out and discussed. The review will also discuss several key questions such as the systematic classification and expression regulation of the ALF genes, as well as the future application of ALFs and ALF-derived peptides.

Caspase-3C gene from red swamp crayfish, Procambarus clarki: Characterization and expression in response to pathogenic infection

The caspase is an essential module in the Drosophila immune deficiency (IMD) pathway, which plays a crucial role in countering pathogen infection. In this study, a gene named PcCaspase-3C was found in Procambarus clarkia with a full-length of 4684 bp, including a 1572 bp opening reading frame, which encoded a putative protein of 523 amino acids. PcCaspase-3C contained a CASc domain constituted of 237 amino acids. The PcCaspase-3C gene was primarily expressed in heart, stomach, and intestine, while less in gonad, hepatopancreas, gills, and hemocytes, with the least expression in muscle. Infection with Staphyloccocus aureus, Vibrio parahaemolyticus or white spot syndrome virus (WSSV) induced an up-regulated expression of PcCaspase-3C in intestine or stomach to varying degrees. When PcCaspase-3C was silenced by double-stranded RNA, the expression of some antimicrobial peptides such as ALF2, ALF5, ALF6, Cru3, Cru4, and Lys was significantly inhibited. In addition, silencing of PcCaspase-3C accelerated infection with WSSV in vivo. According to these results, we suggest that PcCaspase-3C might play a crucial role in the immune response of P. clarkia against pathogenic bacterial and viral infections.

The Two NF-κB Pathways Regulating Bacterial and WSSV Infection of Shrimp

The outbreak of diseases ordinarily results from the disruption of the balance and harmony between hosts and pathogens. Devoid of adaptive immunity, shrimp rely largely on the innate immune system to protect themselves from pathogenic infection. Two nuclear factor-κB (NF-κB) pathways, the Toll and immune deficiency (IMD) pathways, are generally regarded as the major regulators of the immune response in shrimp, which have been extensively studied over the years. Bacterial infection can be recognized by Toll and IMD pathways, which activate two NF-κB transcription factors, Dorsal and Relish, respectively, to eventually lead to boosting the expression of various antimicrobial peptides (AMPs). In response to white-spot-syndrome-virus (WSSV) infection, these two pathways appear to be subverted and hijacked to favor viral survival. In this review, the recent progress in elucidating microbial recognition, signal transduction, and effector regulation within both shrimp Toll and IMD pathways will be discussed. We will also highlight and discuss the similarities and differences between shrimps and their Drosophila or mammalian counterparts. Understanding the interplay between pathogens and shrimp NF-κB pathways may provide new opportunities for disease-prevention strategies in the future.

Beclin-1 is involved in the regulation of antimicrobial peptides expression in Chinese mitten crab Eriocheir sinensis

Beclin-1, the mammalian ortholog of yeast Atg6, plays essential roles in the regulation of various processes, including autophagy, apoptosis, embryonic development and immune responses in vertebrates. However, the information about Beclin-1 in invertebrates especially in crustaceans is still very limited. In the present study, a novel Beclin-1 (designated as EsBeclin-1) was identified from Chinese mitten crab Eriocheir sinensis. The open reading frame of EsBeclin-1 cDNA was of 1,275 bp, encoding a typical APG6 domain. The deduced amino acid sequence of EsBeclin-1 shared high similarity ranging from 42.9% to 63.6% with the previously identified Beclins. In the phylogenetic tree, EsBeclin-1 was firstly clustered with Drosophila melanogaster Atg6 and then assigned into the branch of invertebrate Beclin-1. The mRNA transcripts of EsBeclin-1 were highly expressed in hepatopancreas, hemocytes and gill. After lipopolysaccharide (LPS) and Aeromonas hydrophila stimulations, the relative mRNA expression of EsBeclin-1 in hemocytes was significantly increased from 3 to 24 h with the peak level of 4.70-fold (p < 0.01) and 2.91-fold (p < 0.01) at 6 h, respectively. EsBeclin-1 protein was diffusely distributed in the cytoplasm of crab hemocytes under normal conditions, whereas it displayed predominantly punctuate distribution after LPS stimulation. After EsBeclin-1 was interfered with specific EsBeclin-1-dsRNA, the mRNA transcripts of some antimicrobial peptides, including EsALF2, EsLYZ, EsCrus and EsCrus2 in crab hemocytes were significantly decreased at 6 h post LPS stimulation. These results implicated that EsBeclin-1 played a role in regulating the antimicrobial peptides expressions in the immune responses of E. sinensis.

Effects of environmental stress on shrimp innate immunity and white spot syndrome virus infection

The shrimp aquaculture industry is plagued by disease. Due to the lack of deep understanding of the relationship between innate immune mechanism and environmental adaptation mechanism, it is difficult to prevent and control the diseases of shrimp. The shrimp innate immune system has received much recent attention, and the functions of the humoral immune response and the cellular immune response have been preliminarily characterized. The role of environmental stress in shrimp disease has also been investigated recently, attempting to clarify the interactions among the innate immune response, the environmental stress response, and disease. Both the innate immune response and the environmental stress response have a complex relationship with shrimp diseases. Although these systems are important safeguards, allowing shrimp to adapt to adverse environments and resist infection, some pathogens, such as white spot syndrome virus, hijack these host systems. As shrimp lack an adaptive immune system, immunization therapy cannot be used to prevent and control shrimp disease. However, shrimp diseases can be controlled using ecological techniques. These techniques, which are based on the innate immune response and the environmental stress response, significantly reduce the impact of shrimp diseases. The object of this review is to summarize the recent research on shrimp environmental adaptation mechanisms, innate immune response mechanisms, and the relationship between these systems. We also suggest some directions for future research.

Characterization of an immune deficiency (IMD) homolog from the oriental river prawn, Macrobrachium nipponense

The immune deficiency (IMD) signal pathway mediates innate immunity against Gram-negative bacteria in crustaceans. In the present study, an IMD homolog (MnIMD) from the oriental river prawn, Macrobrachium nipponense was identified. The full-length cDNA of MnIMD was 782bp with an open reading frame of 549 bp that encodes a putative protein of 182 amino acids including a death domain at the C-terminus. Multiple alignment analysis showed that IMDs in prawn M. nipponense and other crustaceans shared high similarity. The recombinant protein of MnIMD was expressed and purified for further functional analyses. Western blot analysis indicated that MnIMD was present in many tissues, but with the highest level in the gills, which was consistent with the qRT-PCR results. After Vibrio parahaemolyticus challenge, MnIMD was significantly induced in gills. RNA interference analysis showed that the IMD pathway was involved in regulating the expression of different antimicrobial peptide (AMP) genes, including Cru4 and Cru6. These results are helpful in promoting research on the innate immunity in M. nipponense.

Identification and functional analysis of immune deficiency (IMD) from Scylla paramamosain: The first evidence of IMD signaling pathway involved in immune defense against bacterial infection in crab species

Immune deficiency (IMD) pathway, one of the most essential pattern recognition receptor signaling pathways, plays vital roles in innate immune responses to eliminate pathogen infection in invertebrates. In the present study, an immune deficiency (IMD) gene and two NF-κB family members, Relish and Dorsal, were identified and characterized in mud crab Scylla paramamosain for the first time. The deduced SpIMD, SpRelish and SpDorsal protein contained conserved death domain and classical NF-κB domains, respectively. Phylogenetic analysis suggested that SpIMD was classified into the invertebrate IMD branch, and SpRelish could be classified into the type I NF-κB class while SpDorsal could be grouped into the type II NF-κB class. Tissue distribution results showed these three genes were ubiquitously expressed in all tested tissues. The expression patterns of IMD signaling pathway and NF-κB genes, including SpIMD, SpIKKβ, SpIKKε, SpRelish and SpDorsal, were distinct when crabs were stimulated with Vibro alginolyticus, indicating that they might be involved in responding to bacterial infection. When SpIMD was silenced by in vivo RNA interference assay, the expression levels of IMD pathway and antimicrobial peptides (AMPs) genes, including SpIKKβ, SpRelish, SpALF1-6 and SpCrustin, were significantly down-regulated (p < 0.05). Correspondingly, the bacteria clearance ability of hemolymph was extremely impaired in IMD silenced crabs. Overall, the IMD played vital roles in innate immune response by regulating the expressions of its down-stream signaling genes and AMPs in S. paramamosain. These findings might pave the way for a better understanding of innate immune system and establish a fundamental network for the IMD signaling pathway in crustaceans.

Shrimp humoral responses against pathogens: antimicrobial peptides and melanization

Diseases have caused tremendous economic losses and become the major problem threatening the sustainable development of shrimp aquaculture. The knowledge of host defense mechanisms against invading pathogens is essential for the implementation of efficient strategies to prevent disease outbreaks. Like other invertebrates, shrimp rely on the innate immune system to defend themselves against a range of microbes by recognizing and destroying them through cellular and humoral immune responses. Detection of microbial pathogens triggers the signal transduction pathways including the NF-κB signaling, Toll and Imd pathways, resulting in the activation of genes involved in host defense responses. In this review, we update the discovery of components of the Toll and Imd pathways in shrimp and their participation in the regulation of shrimp antimicrobial peptide (AMP) synthesis. We also focus on a recent progress on the two most powerful and the best-studied shrimp humoral responses: AMPs and melanization. Shrimp AMPs are mainly cationic peptides with sequence diversity which endues them the broad range of activities against microorganisms. Melanization, regulated by the prophenoloxidase activating cascade, also plays a crucial role in killing and sequestration of invading pathogens. The progress and emerging research on mechanisms and functional characterization of components of these two indispensable humoral responses in shrimp immunity are summarized and discussed. Interestingly, the pattern recognition protein (PRP) crosstalk is evidenced between the proPO activating cascade and the AMP synthesis pathways in shrimp, which enables the innate immune system to build up efficient immune responses.

Crayfish immunity - Recent findings

Freshwater crayfish is an important commodity as well as a successful model for studies on crustacean immunity. Due to the ease with which they are kept and the available methods for hemocyte separation and culture they have proven to be very useful. Here, recent progress regarding pattern recognition, immune effector production and antiviral mechanisms are discussed. Several cases of functional resemblance between vertebrate complement and the crayfish immune reactions are highlighted.

Cloning and analysis of peptidoglycan recognition protein-LC and immune deficiency from the diamondback moth, Plutella xylostella

Peptidoglycan (PGN) exists in both Gram-negative and Gram-positive bacteria as a component of the cell wall. PGN is an important target to be recognized by the innate immune system of animals. PGN recognition proteins (PGRP) are responsible for recognizing PGNs. In Drosophila melanogaster, PGRP-LC and IMD (immune deficiency) are critical for activating the Imd pathway. Here, we report the cloning and analysis of PGRP-LC and IMD (PxPGRP-LC and PxIMD) from diamondback moth, Plutella xylostella (L.), the insect pest of cruciferous vegetables. PxPGRP-LC gene consists of six exons encoding a polypeptide of 308 amino acid residues with a transmembrane region and a PGRP domain. PxIMD cDNA encodes a polypeptide of 251 amino acid residues with a death domain. Sequence comparisons indicate that they are characteristic of Drosophila PGRP-LC and IMD homologs. PxPGRP-LC and PxIMD were expressed in various tissues and developmental stages. Their mRNA levels were affected by bacterial challenges. The PGRP domain of PxPGRP-LC lacks key residues for the amidase activity, but it can recognize two types of PGNs. Overexpression of full-length and deletion mutants in Drosophila S2 cells induced expression of some antimicrobial peptide genes. These results indicate that PxPGRP-LC and PxIMD may be involved in the immune signaling of P. xylostella. This study provides a foundation for further studies of the immune system of P. xylostella.

Co-option of bacteriophage lysozyme genes by bivalve genomes

Eukaryotes have occasionally acquired genetic material through horizontal gene transfer (HGT). However, little is known about the evolutionary and functional significance of such acquisitions. Lysozymes are ubiquitous enzymes that degrade bacterial cell walls. Here, we provide evidence that two subclasses of bivalves (Heterodonta and Palaeoheterodonta) acquired a lysozyme gene via HGT, building on earlier findings. Phylogenetic analyses place the bivalve lysozyme genes within the clade of bacteriophage lysozyme genes, indicating that the bivalves acquired the phage-type lysozyme genes from bacteriophages, either directly or through intermediate hosts. These bivalve lysozyme genes underwent dramatic structural changes after their co-option, including intron gain and fusion with other genes. Moreover, evidence suggests that recurrent gene duplication occurred in the bivalve lysozyme genes. Finally, we show the co-opted lysozymes exhibit a capacity for antibacterial action, potentially augmenting the immune function of related bivalves. This represents an intriguing evolutionary strategy in the eukaryote–microbe arms race, in which the genetic materials of bacteriophages are co-opted by eukaryotes, and then used by eukaryotes to combat bacteria, using a shared weapon against a common enemy.

Regulation of antilipopolysaccharide factors, ALFPm3 and ALFPm6, in Penaeus monodon

ALFPm6, a member of antimicrobial peptide in the antilipopolysaccharide factor (ALF) family from Penaeus monodon, plays important roles in shrimp immunity against pathogens. However, its antimicrobial activity and underlying mechanism have not been reported. The synthetic cyclic ALFPm6#29–52 peptide (cALFPm6#29–52) corresponding to the ALFPm6 LPS-binding domain can agglutinate and exhibited bacterial killing activity toward a Gram-negative bacterium, Escherichia coli 363 and Gram-positive bacteria, Bacillus megaterium, Aerococcus viridans, and Micrococcus luteus, with MIC values of 25–50 μM. Specifically, ALFPm6 and ALFPm3, the most abundant ALF isoforms, are different in terms of gene expression patterns upon pathogen infections. Herein, the regulation of ALFPm3 and ALFPm6 gene expression was studied. The 5′-upstream and promoter sequences were identified and the putative transcription factor (TF)-binding sites were predicted. The narrow down assay indicated that the ALFPm3 promoter and partial promoter of the ALFPm6 active regions were located at nucleotide positions (−814/+302) and (−282/+85), respectively. Mutagenesis of selected TF-binding sites revealed that Rel/NF-κB (−280/−270) of ALFPm3 and C/EBPβ (−88/−78) and Sp1 (−249/−238) sites of ALFPm6 were the activator-binding sites. Knockdown of the PmMyD88 and PmRelish genes in V. harveyi-infected shrimp suggested that the ALFPm3 gene was regulated by Toll and IMD pathways, while the ALFPm6 gene was regulated by the Toll pathway.

Biomolecular changes that occur in the antennal gland of the giant freshwater prawn (Machrobrachium rosenbergii)

In decapod crustaceans, the antennal gland (AnG) is a major primary source of externally secreted biomolecules, and some may act as pheromones that play a major role in aquatic animal communication. In aquatic crustaceans, sex pheromones regulate reproductive behaviours, yet they remain largely unidentified besides the N-acetylglucosamine-1,5-lactone (NAGL) that stimulates male to female attraction. In this study, we used an AnG transcriptome of the female giant freshwater prawn (Macrobrachium rosenbergii) to predict the secretion of 226 proteins, including the most abundantly expressed transcripts encoding the Spaetzle protein, a serine protease inhibitor, and an arthropodial cuticle protein AMP 8.1. A quantitative proteome analysis of the female AnG at intermolt, premolt and postmolt, identified numerous proteins of different abundances, such as the hemocyanin subunit 1 that is most abundant at intermolt. We also show that hemocyanin subunit 1 is present within water surrounding females. Of those metabolites identified, we demonstrate that the NAGL and N-acetylglucosamine (NAG) can bind with high affinity to hemocyanin subunit 1. In summary, this study has revealed components of the female giant freshwater prawn AnG that are released and contribute to further research towards understanding crustacean conspecific signalling.

A sulfated galactans supplemented diet enhances the expression of immune genes and protects against Vibrio parahaemolyticus infection in shrimp

A sulfated galactans (SG) supplemented diet was evaluated for the potential to stimulate immune activity in shrimp Penaeus vannamei (P. vannamei). Shrimp given the SG supplemented diet (0.5, 1 and 2% w/w) for 7 days showed enhanced expression of the downstream signaling mediator of lipopolysaccharide and β-1,3-glucan binding protein (LGBP) and immune related genes including p-NF-κB, IMD, IKKβ and IKKε, antimicrobial peptide PEN-4, proPO-I and II. Following immersion with Vibrio parahaemolyticus (V. parahaemolyticus) for 14 days, the shrimp given the SG supplemented diet (1 and 2% w/w) showed a decrease in bacterial colonies and bacterial toxin gene expression, compared to shrimp given a normal diet, and they reached 50% mortality at day 14. However, shrimp given the normal diet and challenged with the bacteria reached 100% mortality at day 6. SG-fed shrimp increased expression of immune genes related to LGBP signaling at day 1 after the bacterial immersion compared to control (no immersion), which later decreased to control levels. Shrimp on the normal diet also increased expression of immune related genes at day 1 after immersion which however decreased below control levels by day 3. Taken together, the results indicate the efficacy of the SG supplemented diet to enhance the immune activity in shrimp which could offer protection from V. parahaemolyticus infection.

PcToll3 was involved in anti-Vibrio response by regulating the expression of antimicrobial peptides in red swamp crayfish, Procambarus clarkii

Tolls and Toll-like receptors (TLRs) play an important role in host immune defenses by regulating the expression of antimicrobial peptides (AMPs) and cytokines, but the functional differences of crustacean Tolls from Drosophila Tolls or Mammal TLRs are largely unknown. A novel Toll receptor, named PcToll3, was identified from red swamp crayfish, Procambarus clarkii. It was widely expressed in all detected tissues, and its transcript in hemocytes was up-regulated at 12 h after Vibrio parahemolyticus (Vibrio) injection or at 24 h post white spot syndrome virus (WSSV) challenge. After knockdown of PcToll3, the activity of bacterial clearance was inhibited, and the expression levels of AMPs including Crustin1 (Cru1), Anti-lippopolysaccharide factor 1 (ALF1), and Lysozymes1 (Lys1), which could be up-regulated by Vibrio, were all affected. Meanwhile, PcToll3 silencing influenced the expression of myeloid differentiation factor 88 (PcMyd88), tumor necrosis factor-associated factor 6 (PcTRAF6), and PcDorsal, which were the counterparts of Drosophila Toll signaling pathway. Interestingly, PcToll3 silencing inhibited translocation of PcDorsal from cytoplasm to nucleus. Furthermore, the knockdown of PcDorsal also impaired the expression of AMPs after Vibrio challenge. Hence, we concluded that, besides participating in antiviral immunity, PcToll3 might also regulate the expression of Cru1 and Lys1 to participate in anti-Vibrio immune responses by promoting PcDorsal translocation into nucleus.

Next-Generation Sequencing and the Crustacean Immune System: The Need for Alternatives in Immune Gene Annotation

Next-generation sequencing has been a huge benefit to investigators studying non-model species. High-throughput gene expression studies, which were once restricted to animals with extensive genomic resources, can now be applied to any species. Transcriptomic studies using RNA-Seq can discover hundreds of thousands of transcripts from any species of interest. The power and limitation of these techniques is the sheer size of the dataset that is acquired. Parsing these large datasets is becoming easier as more bioinformatic tools are available for biologists without extensive computer programming expertise. Gene annotation and physiological pathway tools such as Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) Orthology enable the application of the vast amount of information acquired from model organisms to non-model species. While noble in nature, utilization of these tools can inadvertently misrepresent transcriptomic data from non-model species via annotation omission. Annotation followed by molecular pathway analysis highlights pathways that are disproportionately affected by disease, stress, or the physiological condition being examined. Problems occur when gene annotation procedures only recognizes a subset, often 50% or less, of the genes differently expressed from a non-model organisms. Annotated transcripts normally belong to highly conserved metabolic or regulatory genes that likely have a secondary or tertiary role, if any at all, in immunity. They appear to be disproportionately affected simply because conserved genes are most easily annotated. Evolutionarily induced specialization of physiological pathways is a driving force of adaptive evolution, but it results in genes that have diverged sufficiently to prevent their identification and annotation through conventional gene or protein databases. The purpose of this manuscript is to highlight some of the challenges faced when annotating crustacean immune genes by using an American lobster (Homarus americanus) transcriptome as an example. Immune genes have evolved rapidly over time, facilitating speciation and adaption to highly divergent ecological niches. Complete and proper annotation of immune genes from invertebrates has been challenging. Modulation of the crustacean immune system occurs in a variety of physiological responses including biotic and abiotic stressors, molting and reproduction. A simple method for the identification of a greater number of potential immune genes is proposed, along with a short introductory primer on crustacean immune response. The intended audience is not the advanced bioinformatic user, but those investigating physiological responses who require rudimentary understanding of crustacean immunological principles, but where immune gene regulation is not their primary interest.

De Novo Transcriptome Analysis Provides Insights into Immune Related Genes and the RIG-I-Like Receptor Signaling Pathway in the Freshwater Planarian (Dugesia japonica)

Background

The freshwater planarian Dugesia japonica (D. japonica) possesses extraordinary ability to regenerate lost organs or body parts. Interestingly, in the process of regeneration, there is little wound infection, suggesting that D. japonica has a formidable innate immune system. The importance of immune system prompted us to search for immune-related genes and RIG-I-like receptor signaling pathways.

Results

Transcriptome sequencing of D. japonica was performed on an IlluminaHiSeq2000 platform. A total of 27,180 transcripts were obtained by Trinity assembler. CEGMA analysis and mapping of all trimmed reads back to the assembly result showed that our transcriptome assembly covered most of the whole transcriptome. 23,888 out of 27,180 transcripts contained ORF (open reading fragment), and were highly similar to those in Schistosoma mansoni using BLASTX analysis. 8,079 transcripts (29.7%) and 8,668 (31.9%) were annotated by Blast2GO and KEGG respectively. A DYNLRB-like gene was cloned to verify its roles in the immune response. Finally, the expression patterns of 4 genes (RIG-I, TRAF3, TRAF6, P38) in the RIG-I-like receptor signaling pathway were detected, and the results showed they are very likely to be involved in planarian immune response.

Conclusion

RNA-Seq analysis based on the next-generation sequencing technology was an efficient approach to discover critical genes and to understand their corresponding biological functions. Through GO and KEGG analysis, several critical and conserved signaling pathways and genes related to RIG-I-like receptor signaling pathway were identified. Four candidate genes were selected to identify their expression dynamics in the process of pathogen stimulation. These annotated transcripts of D. japonica provide a useful resource for subsequent investigation of other important pathways.

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

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

YHV-responsive gene expression under the influence of PmRelish regulation

In animals, infection by Gram-negative bacteria and certain viruses activates the Imd signaling pathway wherein the a NF-κB transcription factor, Relish, is a key regulatory protein for the synthesis of antimicrobial proteins. Infection by yellow head virus (YHV) activates the Imd pathway. To investigate the expression of genes involved in YHV infection and under the influence of PmRelish regulation, RNA interference and suppression subtractive hybridization (SSH) are employed. The genes in forward library expressed in shrimp after YHV infection and under the activity of PmRelish were obtained by subtracting the cDNAs from YHV-infected and PmRelish-knockdown shrimp with cDNAs from YHV-infected shrimp. Opposite subtraction gave a reverse library whereby an alternative set of genes under YHV infection and no PmRelish expression were obtained. Nucleotide sequences of 252 and 99 cDNA clones from the forward and reverse libraries, respectively, were obtained and annotated through blast search against the GenBank sequences. Genes involved in defense and homeostasis were abundant in both libraries, 31% and 23% in the forward and reverse libraries, respectively. They were predominantly antimicrobial proteins, proteinases and proteinase inhibitors. The expression of antimicrobial protein genes, ALFPm3, crustinPm1, penaeidin3 and penaeidin5 were tested under PmRelish silencing and Gram-negative bacterium Vibrio harveyi infection. Together with the results using YHV infection previously reported, the expression of penaeidin5 and also penaeidin3 but not ALFPm3 and crustinPm1 were under the regulation of PmRelish in the Imd pathway.

Involvement of Relish gene from Macrobrachium rosenbergii in the expression of anti-microbial peptides

Relish is an NF-kB transcription factor involved in immune-deficiency (IMD) signal pathway. In this study, a Relish gene (MrRelish) was identified from Macrobrachium rosenbergii. The full length of MrRelish comprises 5072 bp, including a 3510 bp open reading frame encoding a 1169 bp amino acid protein. MrRelish contains a Rel homology domain (RHD), a nucleus localization signal, an IκB-like domain (6 ankyrin repeats), and a death domain. Phylogenetic analysis showed that MrRelish and other Relish from crustaceans belong to one group. MrRelish was expressed in all detected tissues, with the highest expression level in hemocytes and intestines. MrRelish was also upregulated in hepatopancreas at 6 h after Vibrio anguillarum challenge. The over-expression of MrRelish could induce the expression of antimicrobial peptides (AMPs), such as Drosophila Metchnikowin (Mtk), Attacin (Atta), Drosomycin (Drs), and Cecropin (CecA) and shrimp Penaeidin (Pen4). The RNAi of MrRelish in gills showed that the expression of crustin (cru) 2, Cru5, Cru8, lysozyme (Lyso) 1, and Lyso2 was inhibited. However, the expression of anti-lipopolysaccharide factor (ALF) 1 and ALF3 did not change when MrRelish was knocked down. These results indicate that MrRelish may play an important role in innate immune defense against V. anguillarum in M. rosenbergii.

Antimicrobial proteins: From old proteins, new tricks

This review describes the main types of antimicrobial peptides (AMPs) synthesised by crustaceans, primarily those identified in shrimp, crayfish, crab and lobster. It includes an overview of their range of microbicidal activities and the current landscape of our understanding of their gene expression patterns in different body tissues. It further summarises how their expression might change following various types of immune challenges. The review further considers proteins or protein fragments from crustaceans that have antimicrobial properties but are more usually associated with other biological functions, or are derived from such proteins. It discusses how these unconventional AMPs might be generated at, or delivered to, sites of infection and how they might contribute to crustacean host defence in vivo. It also highlights recent work that is starting to reveal the extent of multi-functionality displayed by some decapod AMPs, particularly their participation in other aspects of host protection. Examples of such activities include proteinase inhibition, phagocytosis, antiviral activity and haematopoiesis.

A novel vertebrates Toll-like receptor counterpart regulating the anti-microbial peptides expression in the freshwater crayfish, Procambarus clarkii

Toll-like receptors (TLRs) play an important role in regulation of anti-microbial peptides (AMPs) expression. A novel vertebrates TLR counterpart named PcToll, was firstly identified from the freshwater crayfish, Procambarus clarkii. Phylogenetic analysis showed that PcToll together with Drosophila melanogaster and Anopheles gambiae Toll9 were clustered with human Tolls. PcToll was mainly expressed in hepatopancreas and gills and it also could be detected in hemocytes, heart, stomach and intestine. PcToll was upregulated in hemocytes and gills post 24 h Vibrio anguillarum challenge. In hepatopancreas and intestine, the highest expression level of PcToll could be observed at 12 h V. anguillarum challenge. In hemocytes, PcToll went up post 24 h Staphylococcus aureus challenge and in gills, the expression level of PcToll showed no obvious change from 2 to 24 h S. aureus challenge. In hepatopancreas post 12 h S. aureus challenge, PcToll was upregulated and it showed obvious upregulation post 12 h S. aureus challenge in intestine. RNAi results showed that PcToll was involved in regulation of crustins (Cru1, Cru2), anti-lipopolysaccharide factor 2 (ALF2) and lysozyme 1 (Lys1) expression. Overexpression of PcToll in Drosophila S2 cells could induce Drosophila Attacin (Atta), Metchnikowin (Mtk), Drosomycin (Drs) and shrimp Penaeidin (PEN4) expression. From the results, it could be speculated that PcToll might play important roles in crayfish innate immune defense.

Activation of PmRelish from Penaeus monodon by yellow head virus

Humoral innate immune response against pathogenic infection is partly responsible by the Imd pathway in which a transcription factor Relish relays the infection signals to the nuclei for the expression of antimicrobial proteins. A PmRelish gene which encoded a protein of 1195 amino acids was cloned. The PmRelish was constitutively expressed in all tissues tested and mostly up-regulated upon YHV infection. In hemocytes, the PmRelish expression was up-regulated upon Vibrio harveyi, yellow head virus (YHV) and white spot syndrome virus (WSSV) challenges. Using dsRNA silencing of PmRelish gene, it was shown that the expression of penaeidin5 but not anti-lipopolysaccharide factor ALFPm3, crustinPm1 and penaeidin3 was under the regulation of Imd pathway. Under PmRelish silencing, the shrimp were more susceptible to infection by YHV with the 50% survival rate reduced from about 72 h to 42 h. The PmRelish was detected in the cytoplasm of all the hemocytes from both uninfected and YHV-infected shrimp. The accumulation of activated PmRelish in the nuclei was not clearly observed but the activated PmRelish was detected in the YHV-infected hemocytes by Western blot analysis. Thus, the PmRelish and, hence, the Imd pathway respond to the YHV infection.

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.

Role of evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) in the antibacterial immunity of Marsupenaeus japonicus

The Toll/Toll-like receptor (TLR) signaling pathway has an important role in the innate immunity of animals. Evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) is a protein that functions as an adaptor protein for the Toll/TLR and bone morphogenetic protein signaling pathways. ECSIT is also a key component in the macrophage bactericidal activity of mammals. However, the function of ECSIT in crustaceans remains unclear. In this study, we cloned and identified a functional ECSIT homologue, MjECSIT 1, from kuruma shrimp Marsupenaeus japonicus. The complementary DNA of MjEcsit 1 is 1442 base pairs long, with an open reading frame of 1221 base pairs that encodes a 407-residue polypeptide. Transcripts of MjEcsit 1 are detected in hemocytes, gills, hepatopancreas, stomach, heart, intestines, testes, and ovaries. Such transcripts are upregulated by Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Vibrio anguillarum) injections. The knockdown of MjEcsit 1 by double-stranded RNA injection increases the sensitivity of M. japonicus to S. aureus challenge and weakens the bacterial clearance ability of M. japonicus in vivo. In addition, suppressing MjEcsit 1 restrains the upregulation of two anti-lipopolysaccharide factors by S. aureus injection. The results indicate that MjECSIT 1 is important in the antibacterial immunity of M. japonicus.

The invertebrate midintestinal gland ("hepatopancreas") is an evolutionary forerunner in the integration of immunity and metabolism

The immune system has an impact on the metabolic performance in vertebrates, thus the metabolic effects of immune cells are receiving intense attention today in the biomedical field. However, the evolutionary origin of the immunity-metabolism interaction is still uncertain. In this review, I show that mollusks and crustaceans integrate immune functions to a metabolic organ, the midintestinal gland ("hepatopancreas"). In these animals, the epithelial cells of the midintestinal gland are major sources of immune molecules, such as lectins, hemocyanin, ferritin, antibacterial and antiviral proteins, proteolytic enzymes and nitric oxide. There is crosstalk between midintestinal gland cells and phagocytes, which aids the initiation of the immune response and the clearance of pathogens. The midintestinal gland is thereby an integrated organ of immunity and metabolism. It is likely that immunity was the primary function of the midintestinal gland cells and that their role in the intermediate metabolism has evolved during the course of their further specialization.

Antiviral defense in shrimp: from innate immunity to viral infection

The culture of penaeid shrimp is rapidly developing as a major business endeavor worldwide. However, viral diseases have caused huge economic loss in penaeid shrimp culture industries. Knowledge of shrimp innate immunity and antiviral responses has made important progress in recent years, allowing the design of better strategies for the prevention and control of shrimp diseases. In this study, we have updated information on shrimp antiviral immunity and interactions between shrimp hosts and viral pathogens. Current knowledge and recent progress in immune signaling pathways (e.g., Toll/IMD-NF-κB and JAK-STAT signaling pathways), RNAi, phagocytosis, and apoptosis in shrimp antiviral immunity are discussed. The mechanism of viral infection in shrimp hosts and the interactions between viruses and shrimp innate immune systems are also analyzed.

A new type antimicrobial peptide astacidin functions in antibacterial immune response in red swamp crayfish Procambarus clarkii

A new antibacterial peptide called astacidin was characterized from hemocytes of red swamp crayfish Procambarus clarkii, and designated as PcAst. The full-length cDNA of PcAst contained 828 nucleotides with a polyadenylation sequence and a poly-A tail. PcAst encoded a peptide of 43 amino acids, with a signal peptide of 23 amino acids. The mature peptide contained 20 amino acids, among which four were proline/arginine amino acids. Similarity analysis showed that PcAst shared high identity with astacidin 2 from freshwater crayfish Pacifastacus leniusculus. Quantitative real-time PCR analysis showed that PcAst transcripts were mainly distributed in hemocytes and gills. The time-course expression analysis showed that after Vibrio anguillarum and Staphylococcus aureus injection, the transcripts of PcAst were upregulated in the gills. The synthetic small peptide for mature PcAst displayed inhibitory activity against the growth of some Gram-positive and Gram-negative bacteria. This peptide also had a binding ability to bacterial cell wall components, including peptidoglycan, lipopolysaccharide and lipoteichoic acid. PcAst functioned in the bacterial clearance immune reaction after V. anguillarum and S. aureus infection. These results indicate that PcAst has an important function in antibacterial innate immune response in red swamp crayfish P. clarkii.