Invertebrate immune systems - not homogeneous, not simple, not well understood

Defending against pathogens - immunological priming and its molecular basis in a sea anemone, cnidarian

Cnidarians, in general, are long-lived organisms and hence may repeatedly encounter common pathogens during their lifespans. It remains unknown whether these early diverging animals possess some type of immunological reaction that strengthens the defense response upon repeated infections, such as that described in more evolutionary derived organisms. Here we show results that sea anemones that had previously encountered a pathogen under sub-lethal conditions had a higher survivorship during a subsequently lethal challenge than naïve anemones that encountered the pathogen for the first time. Anemones subjected to the lethal challenge two and four weeks after the sub-lethal exposure presented seven- and five-fold increases in survival, respectively, compared to the naïve anemones. However, anemones challenged six weeks after the sub-lethal exposure showed no increase in survivorship. We argue that this short-lasting priming of the defense response could be ecologically relevant if pathogen encounters are restricted to short seasons characterized by high stress. Furthermore, we discovered significant changes in proteomic profiles between naïve sea anemones and those primed after pathogen exposure suggesting a clear molecular signature associated with immunological priming in cnidarians. Our findings reveal that immunological priming may have evolved much earlier in the tree of life than previously thought.

CgIL17-5, an ancient inflammatory cytokine in Crassostrea gigas exhibiting the heterogeneity functions compared with vertebrate interleukin17 molecules

Interleukin 17 (IL17) is a proinflammatory cytokine that plays an important role in immune response. Recently, five novel IL17 homologs have been identified by screening and analyzing the genome of pacific oyster Crassostrea gigas. In the present study, the functions of CgIL17-5 were investigated by examining the distribution of its mRNA and protein, ligands binding and modulation in immune response. The mRNA expression levels of CgIL17-5 in hemocytes of oysters post twice challenges of Vibrio splendidus were all significantly up-regulated (P < 0.01), while the secondary pathogen infection attenuated the expression level of CgIL17-5 mRNA compared with the primary challenge. CgIL17-5 was found to be located on oyster hemocyte membranes through fluorescence confocal assay. The luciferase reporter assays showed that CgIL17-5 could activate the transfactors NF-κB, CREB and ATF-1, and involve in their signal pathways in HEK293T cells. Meanwhile, CgIL17-5 could augment the IL6 synthesis in HuVEC cells, playing the similar roles as human IL17 in inflammatory response. Additionally, the recombinant CgIL17-5 (rCgIL17-5) could directly bind peptidoglycan (PGN), lipopolysaccharide (LPS), poly (I:C) and β-1,3-glucan, with the highest affinity to PGN, and significantly inhibit the growth of Micrococcus luteus and Escherichia coli. All the results collectively suggested that CgIL17-5, as an ancient inflammatory cytokine, could not only activate signal transduction for the release of other cytokines, but also mediate the clearance of extracellular bacteria in oysters.

Modulation of immune responses of Rhynchophorus ferrugineus (Insecta: Coleoptera) induced by the entomopathogenic nematode Steinernema carpocapsae (Nematoda: Rhabditida)

Aim of this study was to investigate relationships between the red palm weevil (RPW) Rhynchophorus ferrugineus (Olivier) and the entomopathogenic nematode Steinernema carpocapsae (EPN); particularly, the work was focused on the immune response of the insect host in naive larvae and after infection with the EPN. Two main immunological processes have been addressed: the activity and modulation of host prophenoloxidase-phenoloxidase (proPO) system, involved in melanization of not-self and hemocytes recognition processes responsible for not-self encapsulation. Moreover, immune depressive and immune evasive strategies of the parasite have been investigated. Our results suggest that RPW possess an efficient immune system, however in the early phase of infection, S. carpocapsae induces a strong inhibition of the host proPO system. In addition, host cell-mediated mechanisms of encapsulation, are completely avoided by the parasite, the elusive strategies of S. carpocapsae seem to be related to the structure of its body-surface, since induced alterations of the parasite cuticle resulted in the loss of its mimetic properties. S. carpocapsae before the release of its symbiotic bacteria, depress and elude RPW immune defenses, with the aim to arrange a favorable environment for its bacteria responsible of the septicemic death of the insect target.

Potential Response to Selection of HSP70 as a Component of Innate Immunity in the Abalone Haliotis rufescens

Assessing components of the immune system may reflect disease resistance. In some invertebrates, heat shock proteins (HSPs) are immune effectors and have been described as potent activators of the innate immune response. Several diseases have become a threat to abalone farming worldwide; therefore, increasing disease resistance is considered to be a long-term goal for breeding programs. A trait will respond to selection only if it is determined partially by additive genetic variation. The aim of this study was to estimate the heritability (h²) and the additive genetic coefficient of variation (CV_A) of HSP70 as a component of innate immunity of the abalone Haliotis rufescens, in order to assess its potential response to selection. These genetic components were estimated for the variations in the intracellular (in haemocytes) and extracellular (serum) protein levels of HSP70 in response to an immunostimulant agent in 60 full-sib families of H. rufescens. Levels of HSP70 were measured twice in the same individuals, first when they were young and again when they were pre-harvest adults, to estimate the repeatability (R), the h² and the potential response to selection of these traits at these life stages. High HSP70 levels were observed in abalones subjected to immunostimulation in both the intracellular and extracellular haemolymph fractions. This is the first time that changes in serum levels of HSP70 have been reported in response to an immune challenge in molluscs. HSP70 levels in both fractions and at both ages showed low h² and R, with values that were not significantly different from zero. However, HSP70 induced levels had a CV_A of 13.3–16.2% in young adults and of 2.7–8.1% in pre-harvest adults. Thus, despite its low h², HSP70 synthesis in response to an immune challenge in red abalone has the potential to evolve through selection because of its large phenotypic variation and the presence of additive genetic variance, especially in young animals.

Identification of a novel clip domain serine proteinase (Sp-cSP) and its roles in innate immune system of mud crab Scylla paramamosain

Clip domain serine proteinases and their homologs are involved in the innate immunity of invertebrates. To identify the frontline defense molecules against pathogenic infection, we isolated a novel clip domain serine proteinase (Sp-cSP) from the hemocytes of mud crab Scylla paramamosain. The full-length 1362 bp Sp-cSP contains a 1155 bp open reading frame (ORF) encoding 384 amino acids. Multiple alignment analysis showed that the putative amino acid sequence of Sp-cSP has about 52% and 51% identity with Pt-cSP2 (AFA42360) and Pt-cSP3 (AFA42361) from Portunus trituberculatus, respectively, while the similarity with other cSP sequences was lower than 30%. However, all cSP sequences possess a conserved clip domain at the N-terminal and a Tryp-SPc domain at the C-terminal. The genomic organization of Sp-cSP consists of nine exons and eight introns, with some introns containing one or more tandem repeats. RT-PCR results indicated that Sp-cSP transcripts were predominantly expressed in the subcuticular epidermis, muscle and mid-intestine, but barely detectable in the brain and heart. Further, Sp-cSP transcripts were significantly up-regulated after challenge with lipopolysaccharides (LPS), Vibrio parahaemolyticus, polyinosinic polycytidylic acid (PolyI:C) or white spot syndrome virus (WSSV). Moreover, in vitro, the recombinant Sp-cSP revealed a strong antimicrobial activity against a Gram-positive (Staphylococcus aureus) and four Gram-negative (V. parahaemolyticus, Vibrio alginolyticus, Escherichia coli, Aeromonas hydrophila) bacteria in a dose-dependent manner. Taken together, the acute-phase response to immune challenges and the antimicrobial activity assay indicate that Sp-cSP is a potent immune protector and plays an important role in host defense against pathogen invasion in S. paramamosain.

OsHV-1 countermeasures to the Pacific oyster's anti-viral response

The host-pathogen interactions between the Pacific oyster (Crassostrea gigas) and Ostreid herpesvirus type 1 (OsHV-1) are poorly characterised. Herpesviruses are a group of large, DNA viruses that are known to encode gene products that subvert their host's antiviral response. It is likely that OsHV-1 has also evolved similar strategies as its genome encodes genes with high homology to C. gigas inhibitors of apoptosis (IAPs) and an interferon-stimulated gene (termed CH25H). The first objective of this study was to simultaneously investigate the expression of C. gigas and OsHV-1 genes that share high sequence homology during an acute infection. Comparison of apoptosis-related genes revealed that components of the extrinsic apoptosis pathway (TNF) were induced in response to OsHV-1 infection, but we failed to observe evidence of apoptosis using a combination of biochemical and molecular assays. IAPs encoded by OsHV-1 were highly expressed during the acute stage of infection and may explain why we didn't observe evidence of apoptosis. However, C. gigas must have an alternative mechanism to apoptosis for clearing OsHV-1 from infected gill cells as we observed a reduction in viral DNA between 27 and 54 h post-infection. The reduction of viral DNA in C. gigas gill cells occurred after the up-regulation of interferon-stimulated genes (viperin, PKR, ADAR). In a second objective, we manipulated the host's anti-viral response by injecting C. gigas with a small dose of poly I:C at the time of OsHV-1 infection. This small dose of poly I:C was unable to induce transcription of known antiviral effectors (ISGs), but these oysters were still capable of inhibiting OsHV-1 replication. This result suggests dsRNA induces an anti-viral response that is additional to the IFN-like pathway.

Molecular diversity and evolution of defensins in the manila clam Ruditapes philippinarum

Four types of defensins were identified in Manila clam and designated as Rpdef1, Rpdef2, Rpdef3 and Rpdef4, which encoded a polypeptide of 49, 46, 45 and 42 amino acids, respectively. Sequence alignments indicated that Rpdef1 shared 46.9% identity with Rpdef2, 40.8% with Rpdef3, and 34.7% with Rpdef4. Analysis of transcript polymorphism showed that Rpdef3 accounted for about 60% frequency of Rpdefs occurrence in clams from three geographic origins (Dalian, Qingdao and Hangzhou). By quantitative real-time RT-PCR (qRT-PCR) analysis, the transcripts of Rpdefs were mainly detected in hemocytes and they responded sensitively to bacterial challenge in hemocytes. Evolutionary analysis indicated that all Rpdefs were under positive selection with positively selected basic amino acid residues detected in the C-terminal regions, which perhaps have a functional relevance by modifying the charge distribution of Rpdefs. The results also showed some lineages with dN/dS > 1, suggesting positive selection pressures existed in some lineages of phylogeny tree constructed by mollusk defensins. Overall, our results suggest that Rpdefs perhaps played important roles in host defense and positive selection is the major driving force in generating high diversity of defensins in the Manila clam.

The broad pattern recognition spectrum of the Toll-like receptor in mollusk Zhikong scallop Chlamys farreri

Toll-like receptors (TLRs) are among the most studied pattern recognition receptors (PRRs) playing essential roles in innate immune defenses. In the present study, the basic features of CfTLR in mollusk Zhikong scallop Chlamys farreri, including sequence homology, tissue distribution, subcellular localization and ligands spectrum, were investigated to elucidate its pattern recognition. The elements of extracellular domains (ECD) in CfTLR displayed high homology to the corresponding parts of the ECDs in TLRs from Homo sapiens. CfTLR protein was detected in hemocytes, mantle, gills, hepatopancreas, kidney and gonad of the scallops, and it was localized in both the plasma membranes and the lysosomes in HEK293T cells. CfTLR could activate NFκB in response to multiple HsTLR ligands including Pam3CSK4, glucan (GLU), peptidoglycan (PGN), polyriboinosinic:polyribocytidylic acid (poly I:C), Imiquimod and three types of CpG. Additionally, the scallop serum could enhance the induction of NFκB in the CfTLR expressing cells elicited by most PAMPs, including GLU, PGN, Imiquimod and four types of CpG. It could be concluded that this primitive mollusk TLR shared a hybrid function in pattern recognition and could recognize broader ligands than mammalian TLRs, and its mosaic capability of pathogen associated molecular pattern (PAMP) recognition might be based on the basic features of its structure, ligand properties and the assistance of some components in scallop serum.

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.

The ecology, evolution, impacts and management of host-parasite interactions of marine molluscs

Molluscs are economically and ecologically important components of aquatic ecosystems. In addition to supporting valuable aquaculture and wild-harvest industries, their populations determine the structure of benthic communities, cycling of nutrients, serve as prey resources for higher trophic levels and, in some instances, stabilize shorelines and maintain water quality. This paper reviews existing knowledge of the ecology of host-parasite interactions involving marine molluscs, with a focus on gastropods and bivalves. It considers the ecological and evolutionary impacts of molluscan parasites on their hosts and vice versa, and on the communities and ecosystems in which they are a part, as well as disease management and its ecological impacts. An increasing number of case studies show that disease can have important effects on marine molluscs, their ecological interactions and ecosystem services, at spatial scales from centimeters to thousands of kilometers and timescales ranging from hours to years. In some instances the cascading indirect effects arising from parasitic infection of molluscs extend well beyond the temporal and spatial scales at which molluscs are affected by disease. In addition to the direct effects of molluscan disease, there can be large indirect impacts on marine environments resulting from strategies, such as introduction of non-native species and selective breeding for disease resistance, put in place to manage disease. Much of our understanding of impacts of molluscan diseases on the marine environment has been derived from just a handful of intensively studied marine parasite-host systems, namely gastropod-trematode, cockle-trematode, and oyster-protistan interactions. Understanding molluscan host-parasite dynamics is of growing importance because: (1) expanding aquaculture; (2) current and future climate change; (3) movement of non-native species; and (4) coastal development are modifying molluscan disease dynamics, ultimately leading to complex relationships between diseases and cultivated and natural molluscan populations. Further, in some instances the enhancement or restoration of valued ecosystem services may be contingent on management of molluscan disease. The application of newly emerging molecular tools and remote sensing techniques to the study of molluscan disease will be important in identifying how changes at varying spatial and temporal scales with global change are modifying host-parasite systems.

The immune system and its modulation mechanism in scallop

Scallops are a cosmopolitan family of bivalves, and some of them are highly prized as dominant aquaculture species. In the past decades, there have been increasing studies on the basic biology and immunology of scallops, and this review summarizes the research progresses of immune system and its modulation mechanism in scallop. As invertebrate, scallops lack adaptive immunity and they have evolved an array of sophisticated strategies to recognize and eliminate various invaders by employing a set of molecules and cells. It is evident that basic immune reactions such as immune recognition, signal transduction, and effector synthesis involved in immune response are accomplished in a variety of ways. They rely upon an extensive repertoire of phagocytosis, apoptosis and encapsulation of the circulating hemocytes for eliminating invasive pathogens, as well as the production of immune effectors that are active against a large range of pathogens or sensitive for the environmental stress. Furthermore, the molecular constitutions, metabolic pathways and immunomodulation mechanisms of the primitive catecholaminergic, cholinergic, enkephalinergic system and NO system in scallop are also discussed, which can be taken as an entrance to better understand the origin and evolution of the neuroendocrine-immune regulatory network in lower invertebrates.

The immune response of cephalopods from head to foot

Cephalopods are a diverse group of marine molluscs that have proven their worth in a vast array of ways, ranging from their importance within ecological settings and increasing commercial value, to their recent use as model organisms in biological research. However, despite their acknowledged importance, our understanding of basic cephalopod biology does not equate their ecological, societal, and scientific significance. Among these undeveloped research areas, cephalopod immunology stands out because it encompasses a wide variety of scientific fields including many within the biological and chemical sciences, and because of its potential biomedical and commercial relevance. This review aims to address the current knowledge on the topic of cephalopod immunity, focusing on components and functions already established as part of the animals' internal defense mechanisms, as well as identifying gaps that would benefit from future research. More specifically, the present review details both cellular and humoral defenses, and organizes them into sensor, signaling, and effector components. Molluscan, and particularly cephalopod immunology has lagged behind many other areas of study, but thanks to the efforts of many dedicated researchers and the assistance of modern technology, this gap is steadily decreasing. A better understanding of cephalopod immunity will have a positive impact on the health and survival of one of the most intriguing and unique animal groups on the planet, and will certainly influence many other areas of human interest such as ecology, evolution, physiology, symbiosis, and aquaculture.

A novel biomarker for marine environmental pollution of pi-class glutathione S-transferase from Mytilus coruscus

Glutathione S-transferases (GSTs) are the superfamily of phase II detoxification enzymes that play crucial roles in innate immunity. In this study, a pi-class GST homolog was identified from Mytilus coruscus (named as McGST1, KC525103). The full-length cDNA sequence of McGST1 was 621bp with a 5' untranslated region (UTR) of 70bp and a 3'-UTR of 201bp. The deduced amino acid sequence was 206 residues in length with theoretical pI/MW of 5.60/23.72kDa, containing the conserved G-site and diversiform H-site. BLASTn analysis and phylogenetic relationship strongly suggested that this cDNA sequence was a member of pi class GST family. The prediction of secondary structure displayed a preserved N-terminal and a C-terminal comprised with α-helixes. Quantitative real time RT-PCR showed that constitutive expression of McGST1 was occurred, with increasing order in mantle, muscle, gill, hemocyte, gonad and hepatopancreas. The stimulation of bacterial infection, heavy metals and 180CST could up-regulate McGST1 mRNA expression in hepatopancreas with time-dependent manners. The maximum expression appeared at 6h after pathogenic bacteria injected, with 10-fold in Vibrio alginolyticus and 16-fold in Vibrio harveyi higher than that of the control. The highest point of McGST1 mRNA appeared at different time for exposure to copper (10-fold at day 15), cadmium (9-fold at day10) and 180 CST (10-fold at day 15). These results suggested that McGST1 played a significant role in antioxidation and might potentially be used as indicators and biomarkers for detection of marine environmental pollution.

Molecular characterization and expression of a novel Toll gene from the swimming crab Portunus trituberculatus

Tolls/Toll-like receptors (TLRs) are important cell-surface receptors serving as pattern recognition receptors (PRRs) in the Tolls/TLRs signaling pathway of innate immune responses. In the present study, we isolated and characterized a novel Toll gene (PtToll) from Portunus trituberculatus, and further investigated its expression in various tissues of crab hosts challenged with the parasitic dinoflagellate Hematodinium. The full-length cDNA of PtToll was 3745 bp, with a 3012 bp open reading frame (ORF) encoding 1003 amino acids. Conserved domains consist of 15 tandem leucine-rich repeats (LRRs), a single-pass transmembrane segment (TM) and a cytoplasmic Toll/interleukin-1R (TIR) domain. The PtToll protein shared high similarity to other crustacean Tolls and was clustered with the crustacean Tolls in the phylogenetic tree. The PtToll gene was constitutively expressed in various tissues of P. trituberculatus, with the highest expression in hemocytes. After being challenged with the parasite, the transcripts of PtToll reacted immediately with significant alterations in all the tested tissues, and decreased consistently in most of the detected tissues (e.g., hemocytes, gill, heart, and muscle) within 24h. Then the transcripts of PtToll were significantly up-regulated in hemocytes and heart at 48 h, and in hepatopancreas at 48 and 96 h post the parasitic challenge. By 192 h post challenge, the transcriptional level of PtToll indicated a significant suppression or a decreasing trend. The fluctuations of PtToll gene expression suggested that PtToll was closely associated with intrusion of the Hematodinium parasites, and may possess a vital and systematic function in the innate immunity of P. trituberculatus against the parasitic infection.

Crowding of white shrimp Litopenaeus vananmei depresses their immunity to and resistance against Vibrio alginolyticus and white spot syndrome virus

Immunity parameters and the expression levels of several immune-related proteins, including lipopolysaccharide and β-glucan binding protein (LGBP), peroxinectin (PX), intergin β (IB), prophenoloxidase (proPO) I, proPO II, α2-macroglobulin (α2-M), cytosolic mangangese superoxide dismutase (cytMnSOD), mitochondria manganese superoxide dismutase (mtMnSOD), catalase, glutathione peroxidase (GPx), lysozyme, and penaeidin 3a were examined in white shrimp Litopenaeus vannamei reared at stocking densities of 2, 10, 20, 30, and 40 shrimp L(-1) after 3, 6, and 12 h. All immune parameters including haemocyte count, phenoloxidase (PO) activity, respiratory burst (RB), superoxide dismutase (SOD) activity, lysozyme activity, and haemolymph protein were negatively related to density and time. The PO activity, SOD activity, and lysozyme activity of shrimp reared at 10 shrimp L(-1) after 12 h significantly decreased. The transcript levels of these immune-related proteins were down-regulated in shrimp reared at 20, 30, and 40 shrimp L(-1) after 12 h. Phagocytic activity and clearance efficiency to Vibrio alginolyticus were significantly lower in shrimp reared at 30 and 40 shrimp L(-1) after 12 h. The mortality rates of shrimp reared at 20 and 40 shrimp L(-1) were significantly higher than shrimp reared at 2 shrimp L(-1) over 12-144 h and 12-48 h, respectively. Shrimp reared at high densities (>10 shrimp L(-1)) exhibited decreased resistance against pathogens as evidenced by reductions in immune parameters together with decreased expression levels of immune-related proteins, indicating perturbations of the immune system.

Morphology and classification of hemocytes in Pinctada fucata and their responses to ocean acidification and warming

Hemocytes play important roles in the innate immune response and biomineralization of bivalve mollusks. However, the hemocytes in pearl oysters are poorly understood. In the present study, we investigated the morphology and classification of hemocytes in the pearl oyster, Pinctada fucata. Three types of hemocytes were successfully obtained by light microscopy, electron microscopy and flow cytometry methods: small hyalinocytes, large hyalinocytes and granulocytes. The small hyalinocytes are the major hemocyte population. Morphological analyses indicated that these hemocytes have species-specific characterizations. In addition, we assessed the potential effects of ocean acidification (OA) and ocean warming (OW) on the immune parameters and calcium homeostasis of the hemocytes. OA and OW (31 °C) altered pH value of hemolymph, increased the total hemocyte count, total protein content, and percentage of large hyalinocytes and granulocytes, while it decreased the neutral red uptake ability, suggesting active stress responses of P. fucata to these stressors. Exposure to OW (25 °C) resulted in no significant differences, indicating an excellent immune defense to heat stress at this level. The outflow of calcium from hemocytes to hemolymph was also determined, implying the potential impact of OA and OW on hemocyte-mediated biomineralization. This study, therefore, provides insight into the classification and characterization of hemocyte in the pearl oyster, P. fucata, and also reveals the immune responses of hemocytes to OA and OW, which are helpful for a comprehensive understanding of the effects of global climate change on pearl oysters.

Resistance of Black-lip learl oyster, Pinctada margaritifera, to infection by Ostreid herpes virus 1μvar under experimental challenge may be mediated by humoral antiviral activity

Ostreid herpesvirus 1 (OsHV-1) has induced mass mortalities of the larvae and spat of Pacific oysters, Crassostrea gigas, in Europe and, more recently, in Oceania. The production of pearls from the Black-lip pearl oyster, Pinctada margaritifera, represents the second largest source of income to the economies of French Polynesia and many Pacific Island nations that could be severely compromised in the event of a disease outbreak. Coincidentally with the occurrence of OsHV-1 in the southern hemisphere, C. gigas imported from New Zealand and France into French Polynesia tested positive for OsHV-1. Although interspecies viral transmission has been demonstrated, the transmissibility of OsHV-1 to P. margaritifera is unknown. We investigated the susceptibility of juvenile P. margaritifera to OsHV-1 μvar that were injected with tissue homogenates sourced from either naturally infected or healthy C. gigas. The infection challenge lasted 14 days post-injection (dpi) with sampling at 0, 1, 2, 3, 5, 7 and 14 days. Mortality rate, viral prevalence, and cellular immune responses in experimental animals were determined. Tissues were screened by light microscopy and TEM. Pacific oysters were also challenged and used as a positive control to validate the efficiency of OsHV-1 μvar infection. Viral particles and features such as marginated chromatin and highly electron dense nuclei were observed in C. gigas but not in P. margaritifera. Mortality rates and hemocyte immune parameters, including phagocytosis and respiratory burst, were similar between challenged and control P. margaritifera. Herpesvirus-inhibiting activity was demonstrated in the acellular fraction of the hemolymph from P. margaritifera, suggesting that the humoral immunity is critical in the defence against herpesvirus in pearl oysters. Overall, these results suggest that under the conditions of the experimental challenge, P. margaritifera was not sensitive to OsHV-1 μvar and was not an effective host/carrier. The nature and spectrum of activity of the humoral antiviral activity is worthy of further investigation.

Identification and characterization of a novel Foxo transcription factors in Apostichopus japonicus

The forkhead box O (Foxo) transcription factors are involved in multiple signaling pathways and play key roles in immunoregulation in vertebrates. In the present study, we firstly identified a novel Foxo gene in Apostichopus japonicus coelomocytes using transcriptome sequencing and RACE approaches (denoted as AjFoxo). The full-length cDNA of AjFoxo was of 2248 bp with a 5' untranslated region (UTR) of 177 bp, a 3' UTR of 367 bp and an ORF of 1704 bp encoding a polypeptide of 567 amino acid residues. The highly conserved forkhead domain was also identified in AjFoxo with remarkably higher degree of structural conservation. AjFoxo transcripts could be detected in all examined tissues with predominant expression in the coelomocytes and muscle, and slightly weak in the tissues of tentacle, intestine and respiratory trees. Concerning the time-course expression of AjFoxo in coelomocytes, the relative expression of AjFoxo was dramatically decreased to 0.44-fold at 48 h compared with that in the control group after Vibrio splendidus challenge, which was consistent with that of AjIκB. RNA interference of AjFoxo in primary coelomocytes also significantly depressed the relative expression of AjIκB with a 0.37-fold decrease compared with control group. Taken together, these results indicated that AjFoxo was a novel immune regulator and might be involved in the processes of anti-bacteria response in sea cucumber through activating the transcription of AjIκB.

Function of a novel C-type lectin with two CRD domains from Macrobrachium rosenbergii in innate immunity

C-type lectins play crucial roles in innate immunity. In the present study, a novel C-type lectin gene, designated as MrCTL, was identified from Macrobrachium rosenbergii. MrCTL contains 2 carbohydrate-recognition domains (CRDs), namely MrCRD1 and MrCRD2. The MrCRD1 contains a QEP motif and MrCRD2 contains a motif of EPD. MrCTL was mainly expressed in the hepatopancreas. The expression level of MrCTL in hepatopancreas was significantly upregulated after a challenge with Vibrio parahaemolyticus or White spot syndrome virus (WSSV). The recombinant MrCTL, MrCRD1 and MrCRD2 have an ability to agglutinate both Gram-negative (V. parahaemolyticus) and Gram-positive bacteria (Staphylococcus aureus) in a calcium dependent manner. The recombinant MrCTL, MrCRD1 and MrCRD2 bind directly to all tested microorganisms. All these results suggested that MrCTL may have important roles in immune defense against invading pathogens in prawns.

How do hosts react to endosymbionts? A new insight into the molecular mechanisms underlying the Wolbachia-host association

Wolbachia is an intracellular bacterium that has aroused intense interest because of its ability to alter the biology of its host in diverse ways. In the two-spotted spider mite, Tetranychus urticae, Wolbachia can induce complex cytoplasmic incompatibility (CI) phenotypes and fitness changes, although little is known about the mechanisms. In the present study, we selected a strain of T. urticae, in which Wolbachia infection was associated with strong CI and enhanced female fecundity, to investigate changes in the transcriptome of T. urticae in Wolbachia-infected vs. uninfected lines. The responses were found to be sex-specific, with the transcription of 251 genes being affected in females and 171 genes being affected in males. Some of the more profoundly affected genes in both sexes were lipocalin genes and genes involved in oxidation reduction, digestion and detoxification. Several of the differentially expressed genes have potential roles in reproduction. Interestingly, unlike certain Wolbachia transinfections in novel hosts, the Wolbachia-host association in the present study showed no clear evidence of host immune priming by Wolbachia, although a few potential immune genes were affected.

Maternal immune transfer in mollusc

Maternal immunity refers to the immunity transferred from mother to offspring via egg, playing an important role in protecting the offspring at early life stages and contributing a trans-generational effect on offspring's phenotype. Because fertilization is external in most of the molluscs, oocytes and early embryos are directly exposed to pathogens in the seawater, and thus maternal immunity could provide a better protection before full maturation of their immunological systems. Several innate immune factors including pattern recognition receptors (PRRs) like lectins, and immune effectors like lysozyme, lipopolysaccharide binding protein/bacterial permeability-increasing proteins (LBP/BPI) and antioxidant enzymes have been identified as maternally derived immune factors in mollusc eggs. Among these immune factors, some maternally derived lectins and antibacterial factors have been proved to endue mollusc eggs with effective defense ability against pathogen infection, while the roles of other factors still remain untested. The physiological condition of mollusc broodstock has a profound effect on their offspring fitness. Many other factors such as nutrients, pathogens, environment conditions and pollutants could exert considerable influence on the maternal transfer of immunity. The parent molluscs which have encountered an immune stimulation endow their offspring with a trans-generational immune capability to protect them against infections effectively. The knowledge on maternal transfer of immunity and the trans-generational immune effect could provide us with an ideal management strategy of mollusc broodstock to improve the immunity of offspring and to establish a disease-resistant family for a long-term improvement of cultured stocks.

Digenean-gastropod host associations inform on aspects of specific immunity in snails

Gastropod immunology is informed importantly by the study of the frequent encounters snails endure with digeneans (digenetic trematodes). One of the hallmarks of gastropod-digenean associations is their specificity: any particular digenean parasite species is transmitted by a limited subset of snail taxa. We discuss the nature of this specificity, including its immunological basis. We then review studies of the model gastropod Biomphalaria glabrata indicating that the baseline responses of snails to digeneans can be elevated in a specific manner. Studies incorporating molecular and functional approaches are then highlighted, and are further suggestive of the capacity for specific gastropod immune responses. These studies have led to the compatibility polymorphism hypothesis: the interactions between diversified fibrinogen-related proteins (FREPs) and diverse carbohydrate-decorated polymorphic parasite antigens determine recognition and trigger specific immunity. Complex glycan structures are also likely to play a role in the host specificity typifying snail-digenean interactions. We conclude by noting the dynamic and consequential interactions between snails and digeneans can be considered as drivers of diversification of digenean parasites and in the development and maintenance of specific immunity in gastropods.

Somatic and Germline Diversification of a Putative Immunoreceptor within One Phylum: Dscam in Arthropods

Arthropod Dscam, the homologue of the human Down Syndrome cell adhesion molecule, is a receptor used by the nervous and immune systems. Unlike in vertebrates, evolutionary pressure has selected and maintained a vast Dscam diversity of isoforms, known to specifying neuronal identity during the nervous system differentiation. This chapter examines the different modes of Dscam diversification in the context of arthropods' evolution and that of their immune system, where its role is controversial. In the single Dscam gene of insects and crustaceans, mutually exclusive alternative splicing affects three clusters of duplicated exons encoding the variable parts of the receptor. The Dscam gene produces over 10,000 isoforms. In the more basal arthropods such as centipedes, Dscam diversity results from a combination of many germline genes (over 80) with, in about half of those, the possibility of alternative splicing affecting only one exon cluster. In the even more basal arthropods, such as chelicerates, no splicing possibility is detected, but there exist dozens of germline Dscam genes. Compared to controlling the expression of multiple germline genes, the somatic mutually alternative splicing within a single gene may offer a simplified way of expressing a large Dscam repertoire. Expressed by hemocytes, Dscam is considered a phagocytic receptor but is also encountered in solution. More information is necessary about its binding to pathogens, its role in phagocytosis, its possible role in specifying hemocyte identity, its kinetics of expression, and the regulation of its RNA splicing to understand how its diversity is linked to immunity.

Characterization of two regulators of the TNF-α signaling pathway in Apostichopus japonicus: LPS-induced TNF-α factor and baculoviral inhibitor of apoptosis repeat-containing 2

The TNF-α signaling cascade is involved in the regulation of a variety of biological processes, including cell proliferation, differentiation, apoptosis and the immune response in vertebrates. Here, two regulatory genes, lipopolysaccharide-induced tumor necrosis factor α factor (LITAF) and baculoviral inhibitor of apoptosis repeat-containing 2 (BIRC2), were identified in coelomocytes from the sea cucumber Apostichopus japonicus by RNA-seq and RACE (denoted as AjLITAF and AjBIRC2, respectively). The full-length cDNA of AjLITAF was 1417 bp, with a 5' untranslated region (UTR) of 189 bp, a 3' UTR of 637 bp with one cytokine RNA instability motif (ATTTA) and an open reading frame (ORF) of 591 bp encoding a polypeptide of 196 amino acid residues and a predicted molecular weight of 22.1 kDa. The partial AjBIRC2 cDNA was 2324 bp with a 5' UTR of 145 bp, a 3' UTR of 469 bp and a complete ORF of 1710 bp encoding a polypeptide of 569 amino acid residues. Analysis of the deduced amino acid sequences revealed that both genes shared a remarkably high degree of structural conservation with their mammalian orthologs, including a highly conserved LITAF domain in AjLITAF and three types of BIR domains in AjBIRC2. Spatial expression analysis revealed that AjLITAF and AjBIRC2 were expressed at a slightly lower level in the intestine and tentacle tissues compared with the other four tissues examined. After challenging the sea cucumbers with Vibrio splendidus, the expression levels of AjLITAF and AjBIRC2 in coelomocytes were increased by 2.65-fold at 6 h and 1.76-fold at 24 h compared with the control group. In primary cultured coelomocytes, a significant increase in the expression of AjLITAF and AjBIRC2 was detected after 6 h of exposure to 1 µg mL(-1) LPS. Together, these results suggest that AjLITAF and AjBIRC2 might be involved in the sea cucumber immune response during the course of a pathogenic infection or exposure to pathogen-associated molecular pattern (PAMP) molecules.

Endogenous molecules induced by a pathogen-associated molecular pattern (PAMP) elicit innate immunity in shrimp

Invertebrates rely on an innate immune system to combat invading pathogens. The system is initiated in the presence of cell wall components from microbes like lipopolysaccharide (LPS), β-1,3-glucan (βG) and peptidoglycan (PG), altogether known as pathogen-associated molecular patterns (PAMPs), via a recognition of pattern recognition protein (PRP) or receptor (PRR) through complicated reactions. We show herein that shrimp hemocytes incubated with LPS, βG, and PG caused necrosis and released endogenous molecules (EMs), namely EM-L, EM-β, and EM-P, and found that shrimp hemocytes incubated with EM-L, EM-β, and EM-P caused changes in cell viability, degranulation and necrosis of hemocytes, and increased phenoloxidase (PO) activity and respiratory burst (RB) indicating activation of immunity in vitro. We found that shrimp receiving EM-L, EM-β, and EM-P had increases in hemocyte count and other immune parameters as well as higher phagocytic activity toward a Vibrio pathogen, and found that shrimp receiving EM-L had increases in proliferation cell ratio and mitotic index of hematopoietic tissues (HPTs). We identified proteins of EMs deduced from SDS-PAGE and LC-ESI-MS/MS analyses. EM-L and EM-P contained damage-associated molecular patterns (DAMPs) including HMGBa, HMGBb, histone 2A (H2A), H2B, and H4, and other proteins including proPO, Rab 7 GPTase, and Rab 11 GPTase, which were not observed in controls (EM-C, hemocytes incubated in shrimp salt solution). We concluded that EMs induced by PAMPs contain DAMPs and other immune molecules, and they could elicit innate immunity in shrimp. Further research is needed to identify which individual molecule or combined molecules of EMs cause the results, and determine the mechanism of action in innate immunity.

Novel myeloid differentiation factor 88, EsMyD88, exhibits EsTube-binding activity in Chinese mitten crab Eriocheir sinensis

Myeloid differentiation factor 88 (MyD88) is a universal and essential adapter protein that participates in the activation of the Toll-like receptor/interleukin-1 receptor-mediated signaling pathway. In the present study, a new MyD88 gene (named EsMyD88) was identified in the Chinese mitten crab Eriocheir sinensis. The cDNA of EsMyD88 was 2210 bp long with a 1416 bp open reading frame that encoded a protein with 472 amino acids. Predicted EsMyD88 protein had a death domain at the N-terminal and a TIR domain at the C-terminal. BLASTP and phylogenetic analysis results showed that EsMyD88 was clustered in one group together with other crustaceans MyD88 (SpMyD88, FcMyD88, LvMyD88, and LvMyD88-1). EsMyD88 was detected in all the examined tissues of healthy crabs, and was mainly expressed in the hemocytes and nerves. When normal crabs were challenged with lipopolysaccharide, peptidoglycan, Staphylococcus aureus, Vibrio parahaemolyticus, or Aeromonas hydrophila, the expression levels of EsMyD88 significantly increased either in the hepatopancreas or hemocytes. Results of the pull-down assay showed that EsMyD88 could bind to downstream cytosolic adaptor EsTube. Overexpression of EsMyD88 protein in Drosophila Schneider 2 cells led to the activation of antimicrobial peptide genes. RNA interference assay showed that EsMyD88 is involved in regulating the transcription of ALF1 and ALF2, Cru1 and Cru2, and Lys in crab challenged with V. parahaemolyticus. All the results mentioned earlier indicated that EsMyD88 gene has a key function in antibacterial innate immune defense.

Toll-pathway in tiger shrimp (Penaeus monodon) responds to white spot syndrome virus infection: evidence through molecular characterisation and expression profiles of MyD88, TRAF6 and TLR genes

The Toll-pathway plays key roles in regulating the innate immune response in invertebrates. Myeloid differentiation factor 88 (MyD88) and Tumour necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) are key molecules in this signalling pathway. To investigate the role of Toll-pathway in innate immune response of shrimp, Penaeus monodon, MyD88 (PmMyD88) and TRAF6 (PmTRAF6) were identified and characterised. PmMyD88 cDNA is 1716 bp long with an open reading frame (ORF) of 1449 bp encoding a putative protein of 482 amino acids, with a death domain, a TIR domain and C-terminal extension domain. PmTRAF6 cDNA is 2563 bp long with an ORF of 1785 bp (594 amino acids) with an N-terminal RING-type zinc finger domain, two TRAF-type zinc finger domains, a coiled region and a MATH domain. In healthy shrimp, PmMyD88, PmTRAF6 and PmToll were detected in 15 tissues with the highest expression in midgut, eyestalk and lymphoid organ, respectively. Responses of these genes to WSSV in experimentally-infected P. monodon as well as in cultured haemocytes and also effect of poly I:C on the gene expression in vitro was investigated at six time-points in seven tissues. PmToll showed significant up-regulation at all time-points of infection in six tissues and until 24 h post-infection in vitro. However, poly I:C-induced haemocytes showed up-regulation of the gene until 48 h post-exposure. WSSV caused significant up-regulation of PmMyD88 in most of the tissues tested. The virus challenge as well as poly I:C induction in vitro also resulted in significant up-regulation of the gene. Up-regulated expression of PmTRAF6 was detected in haemocytes and lymphoid organ at late stage of infection. In vitro virus challenge showed significant up-regulation of PmTRAF6 at almost all time-points whereas no significant change in the expression was observed on poly I:C induction. The responses of these key genes, observed in the present study, suggest that Toll-pathway as a whole may play a crucial role in the immune response against viruses in shrimp.

HdhCTL1 is a novel C-type lectin of abalone Haliotis discus hannai that agglutinates Gram-negative bacterial pathogens

C-type lectins (CTLs) are Ca(2+)-dependent carbohydrate recognition proteins, which play important roles in the innate immunity of both vertebrates and invertebrates. In this study, we identified and characterized a C-type lectin (named HdhCTL1) from Pacific abalone, Haliotis discus hannai. HdhCTL1 is composed of 176 amino acid residues and shares low (23.9%) identity with the known CTL of abalone. HdhCTL1 possesses a putative signal peptide and a carbohydrate-recognition domain (CRD) typical of CTLs. The CRD of HdhCTL1 contains four disulfide bond-forming cysteine residues that are highly conserved in CTLs. HdhCTL1 mRNA was detected in a wide range of tissues and expressed abundantly in the digestive gland. Experimental infection with the bacterial pathogen Vibrio anguillarum significantly upregulated HdhCTL1 expression in a time-dependent manner. Recombinant HdhCTL1 (rHdhCTL1) purified from Escherichia coli was able to agglutinate Gram-negative bacterial pathogens. The agglutinating ability of rHdhCTL1 was abolished in the presence of mannose. These results suggest that HdhCTL1 is a novel CTL which is likely to be involved in host defense against bacterial infection.

Immune-directed support of rich microbial communities in the gut has ancient roots

The animal gut serves as a primary location for the complex host-microbe interplay that is essential for homeostasis and may also reflect the types of ancient selective pressures that spawned the emergence of immunity in metazoans. In this review, we present a phylogenetic survey of gut host-microbe interactions and suggest that host defense systems arose not only to protect tissue directly from pathogenic attack but also to actively support growth of specific communities of mutualists. This functional dichotomy resulted in the evolution of immune systems much more tuned for harmonious existence with microbes than previously thought, existing as dynamic but primarily cooperative entities in the present day. We further present the protochordate Ciona intestinalis as a promising model for studying gut host-bacterial dialogue. The taxonomic position, gut physiology and experimental tractability of Ciona offer unique advantages in dissecting host-microbe interplay and can complement studies in other model systems.

Transcriptional changes in Manila clam (Ruditapes philippinarum) in response to Brown Ring Disease

Brown Ring Disease (BRD) is a bacterial infection affecting the economically-important clam Ruditapes philippinarum. The disease is caused by a bacterium, Vibrio tapetis, that colonizes the edge of the mantle, altering the biomineralization process and normal shell growth. Altered organic shell matrices accumulate on the inner face of the shell leading to the formation of the typical brown ring in the extrapallial space (between the mantle and the shell). Even though structural and functional changes have been described in solid (mantle) and fluid (hemolymph and extrapallial fluids) tissues from infected clams, the underlying molecular alterations and responses remain largely unknown. This study was designed to gather information on clam molecular responses to the disease and to compare focal responses at the site of the infection (mantle and extrapallial fluid) with systemic (hemolymph) responses. To do so, we designed and produced a Manila clam expression oligoarray (15K Agilent) using transcriptomic data available in public databases and used this platform to comparatively assess transcriptomic changes in mantle, hemolymph and extrapallial fluid of infected clams. Results showed significant regulation in diseased clams of molecules involved in pathogen recognition (e.g. lectins, C1q domain-containing proteins) and killing (defensin), apoptosis regulation (death-associated protein, bcl-2) and in biomineralization (shell matrix proteins, perlucin, galaxin, chitin- and calcium-binding proteins). While most changes in response to the disease were tissue-specific, systemic alterations included co-regulation in all 3 tested tissues of molecules involved in microbe recognition and killing (complement-related factors, defensin). These results provide a first glance at molecular alterations and responses caused by BRD and identify targets for future functional investigations.

Single sea urchin phagocytes express messages of a single sequence from the diverse Sp185/333 gene family in response to bacterial challenge

Immune systems in animals rely on fast and efficient responses to a wide variety of pathogens. The Sp185/333 gene family in the purple sea urchin, Strongylocentrotus purpuratus, consists of an estimated 50 (±10) members per genome that share a basic gene structure but show high sequence diversity, primarily due to the mosaic appearance of short blocks of sequence called elements. The genes show significantly elevated expression in three subpopulations of phagocytes responding to marine bacteria. The encoded Sp185/333 proteins are highly diverse and have central effector functions in the immune system. In this study we report the Sp185/333 gene expression in single sea urchin phagocytes. Sea urchins challenged with heat-killed marine bacteria resulted in a typical increase in coelomocyte concentration within 24 h, which included an increased proportion of phagocytes expressing Sp185/333 proteins. Phagocyte fractions enriched from coelomocytes were used in limiting dilutions to obtain samples of single cells that were evaluated for Sp185/333 gene expression by nested RT-PCR. Amplicon sequences showed identical or nearly identical Sp185/333 amplicon sequences in single phagocytes with matches to six known Sp185/333 element patterns, including both common and rare element patterns. This suggested that single phagocytes show restricted expression from the Sp185/333 gene family and infers a diverse, flexible, and efficient response to pathogens. This type of expression pattern from a family of immune response genes in single cells has not been identified previously in other invertebrates.

In vitro interactions between the defense systems of resistant and susceptible Biomphalaria alexandrina and sporocysts of Schistosoma mansoni

Biomphalaria species that act as an intermediate host for Schistosoma mansoni have different degrees of susceptibility and different internal defense system responses against parasites. Of these species, Biomphalaria alexandrina represents the only intermediate host in Egypt. Given the limited data on the efficacy of the B. alexandrina internal defense system in comparison to that of other species, we sought to better understand its defense against S. mansoni. We performed in vitro hemocyte adherence assay using whole hemolymph and in vitro reaction using the hemocyte-free hemolymph of susceptible and resistant snails against transformed mother sporocysts. The results demonstrated that the interacting factors between the parasite and the hemolymph of the resistant and susceptible snails do not act in a similar manner. Destruction of the parasite was a restricted function of the hemocytes among resistant snails only. This study demonstrates the key role played by snail hemocytes as a first line of defense against the parasite. The incubation of the hemocyte-free hemolymph of both susceptible and resistant snails with the sporocysts did not lead to any changes in the sporocysts shape or integrity. This immunological variance demonstrated between susceptible and resistant snails could be useful to differentiate between susceptible and resistant snails in future field studies. In addition, the results may help further studies to explain the process of attraction, encapsulation and subsequent killing of S. mansoni in its intermediate host.

Cloning and characterization of two different L-type lectin genes from the Chinese mitten crab Eriocheir sinensis

L-type lectins contain a leguminous lectin domain and bind to high-mannose type oligosaccharides. In the secretory pathway, L-type lectins play crucial functions in the trafficking, sorting, and targeting of maturing glycoproteins. This study identified two novel L-type lectins, designated as EsERGIC-53 and EsVIP36, from the Chinese mitten crab Eriocheir sinensis. The complete nucleotide sequence of ERGIC-53 cDNA was 1955 bp, containing a 1506 bp open reading frame (ORF) encoding a putative protein of 501 deduced amino acids. The full-length cDNA of VIP36 was 3474 bp with a 984 bp ORF encoding a 327-amino acid peptide. The deduced ERGIC-53 and VIP36 proteins contained a putative signal peptide and an L-type lectin-like domain. Phylogenetic analysis showed that ERGIC-53 and VIP36 belonged to different clades of L-type lectin family. Reverse transcription PCR showed that ERGIC-53 and VIP36 were expressed in all tested tissues. Quantitative real-time RT-PCR analysis revealed that ERGIC-53 and VIP36 transcripts in hepatopancreas were significantly induced at various time points after infection with lipopolysaccharide (LPS), peptidoglycan (PGN), Staphylococcus aureus, Vibrio parahaemolyticus, and Aeromonas hydrophila. A bacterium-binding experiment showed that both ERGIC-53 and VIP36 could bind to different microbes. Sugar binding assay revealed that these lectins could also bind to the glycoconjugates of bacteria surface, such as LPS, PGN, d-Mannose, and N-Acetyl-d-mannosamine. Moreover, these two L-type lectins agglutinated bacteria in a calcium-dependent manner, and both exerted the ability of facilitating the clearance of injected bacteria V. parahaemolyticus in the crab. Our results suggested that ERGIC-53 and VIP36 functioned as pattern recognition receptors in the immune system of E. sinensis.

Hemocyte morphology and phagocytic activity in the common cuttlefish (Sepia officinalis)

Little is known about the immune system of cephalopods, in spite of their many highly derived characters within the molluscan clade, including a vertebrate-like high-pressure closed circulatory system. Further the economic importance of cephalopod fisheries, potential for aquaculture, and use as ecotoxicology models demand a thorough understanding of their immune system. In this study, we present a comprehensive characterization of hemocytes in the common cuttlefish Sepia officinalis. Cytological stainings, electron microscopy- and flow cytometry-observations highlight a single granulocyte population with various densities of eosinophilic granules and unstained vesicles. These hemocytes contain acid phosphatase-, lysozyme- and proPO system enzymes, and have high activity in bead phagocytosis assays. Interestingly, bead pre-incubation in plasma results in time-dependent aggregation perhaps resulting from hemocyanin-coating, and decrease in phagocytosis. This study provides the basis for understanding hemocyte-mediated immunity in the common cuttlefish, and essential background for future studies on cephalopod immunity.

Deep sequencing of the scallop Chlamys farreri transcriptome response to tetrabromobisphenol A (TBBPA) stress

Tetrabromobisphenol-A (TBBPA) is currently the most widely used brominated flame retardant (BFR) and has been proven to have a very high toxicity to aquatic organisms including bivalves. However, molecular responses to TBBPA in bivalve remain largely unknown. Novel high-throughput deep sequencing technology has been a powerful tool for looking at molecular responses to toxicological stressors in organisms. Using Illumina's digital gene expression (DGE) system, we investigated TBBPA-induced transcriptome response in the digestive gland tissue of scallop Chlamys farreri. In total, 173 and 266 genes were identified as significantly up- or down-regulated, respectively. Functional analysis based on gene ontology (GO) classification system and Kyoto Encyclopedia of Genes and Genomes (KEGG) database revealed that TBBPA significantly altered the expression of genes involved in stress response, detoxification, antioxidation, and innate immunity which were extensively discussed. In particular, evidence for the endocrine disrupting effect of TBBPA on bivalve was first obtained in this study. Quantitative real-time PCR was performed to ascertain the mRNA expression of several genes identified by the DGE analysis. The results of this study may serve as a basis for future research on molecular mechanism of toxic effects of TBBPA on marine bivalves.

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

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

Occurrence and expression of bacterial human virulence gene homologues in natural soil bacteria

The presence and in vitro expression of homologues to 22 bacterial human virulence determinants amongst culturable soil bacteria were investigated. About 25% of the bacterial isolates contained virulence gene homologues representing toxin (hblA, cytK2), adhesin (fimH), regulator (phoQ) and resistance (yfbI) determinants in pathogenic bacteria. The homologues of the toxin genes were found in Actinobacteria and Firmicutes (hblA), and in Firmicutes and Alpha- and Gammaproteobacteria (cytK2). The homologues to the type 1 fimbrial adhesin gene, fimH, and the L-Ara4N transferase gene, yfbI, were observed in Actinobacteria, Firmicutes and Gammaproteobacteria. The regulator gene, phoQ, was only found in Gammaproteobacteria. The presence of cytK2 in Alpha- and Gammaproteobacteria, fimH in Actinobacteria and Firmicutes, and hblA in Actinobacteria has not previously been described. A close sequence similarity (84-100%) was observed between the genes of environmental and clinical isolates, and expression assays suggested that the genes in some cases were expressed in vitro. The presence of functional virulence gene homologues underpins their importance for the survival of environmental bacteria. Furthermore, the high degree of sequence conservation to clinical sequences indicates that natural environments may be 'evolutionary cribs' of emerging pathogens.

Relationship between phylogeny and immunity suggests older Caribbean coral lineages are more resistant to disease

Diseases affect coral species fitness and contribute significantly to the deterioration of coral reefs. The increase in frequency and severity of disease outbreaks has made evaluating and determining coral resistance a priority. Phylogenetic patterns in immunity and disease can provide important insight to how corals may respond to current and future environmental and/or biologically induced diseases. The purpose of this study was to determine if immunity, number of diseases and disease prevalence show a phylogenetic signal among Caribbean corals. We characterized the constitutive levels of six distinct innate immune traits in 14 Caribbean coral species and tested for the presence of a phylogenetic signal on each trait. Results indicate that constitutive levels of some individual immune related processes (i.e. melanin concentration, peroxidase and inhibition of bacterial growth), as well as their combination show a phylogenetic signal. Additionally, both the number of diseases affecting each species and disease prevalence (as measures of disease burden) show a significant phylogenetic signal. The phylogenetic signal of immune related processes, combined with estimates of species divergence times, indicates that among the studied species, those belonging to older lineages tend to resist/fight infections better than more recently diverged coral lineages. This result, combined with the increasing stressful conditions on corals in the Caribbean, suggest that future reefs in the region will likely be dominated by older lineages while modern species may face local population declines and/or geographic extinction.

The immunomodulation of a novel tumor necrosis factor (CgTNF-1) in oyster Crassostrea gigas

Tumor necrosis factor (TNF) is one of the most important cytokines involved in many processes in both vertebrate and invertebrate. In the present study, a new tumor necrosis factor with a typical TNF domain was identified in oyster Crassostrea gigas (designated CgTNF-1). CgTNF-1 shared low sequence identity and similarity with the TNF superfamily members from other vertebrate and invertebrate. After LPS stimulation, the mRNA expression of CgTNF-1 in haemocytes increased significantly and peaked at 12h (1.39±0.12, P<0.05) post treatment, and the expression of CgTNF-1 protein in haemolymph also increased obviously during 6-12h. When the oyster haemocytes were incubated with rCgTNF-1, its apoptosis and phagocytosis rate were both effectively induced and peaked at 12h post the treatment of rCgTNF-1 with the concentration of 100ngmL(-1) (23.3±3%, P<0.01), 50ngmL(-1) (5.3±0.6%, P<0.05) and 10ngmL(-1) (6.7±1.2%, P<0.05), respectively. After the co-stimulation of LPS and rCgTNF-1, the apoptosis and phagocytosis rate of oyster haemocytes, and the activities of PO and lysozyme in the haemolymph all increased significantly, and reached the peak at 12h (apoptosis rate 26.7±1.5%, P<0.01), 12h (phagocytosis rate 8.3±0.6%, P<0.01), 6h (PO 1.11±0.01Umg prot(-1), P<0.01) and 12h (lysozyme 168.9±8.3Umg prot(-1), P<0.05), respectively, which were significantly higher than that in the LPS group. Furthermore, the anti-bacteria activity in the LPS+TNF group was significantly higher than that in the LPS group during 6-12h. All the results collectively indicated that CgTNF-1 was involved in the oyster immunity and played a crucial role in the modulation of immune response including apoptosis and phagocytosis of haemocytes, and regulation of anti-bacterial activity as well as the activation of immune relevant enzymes.

No more non-model species: the promise of next generation sequencing for comparative immunology

Next generation sequencing (NGS) allows for the rapid, comprehensive and cost effective analysis of entire genomes and transcriptomes. NGS provides approaches for immune response gene discovery, profiling gene expression over the course of parasitosis, studying mechanisms of diversification of immune receptors and investigating the role of epigenetic mechanisms in regulating immune gene expression and/or diversification. NGS will allow meaningful comparisons to be made between organisms from different taxa in an effort to understand the selection of diverse strategies for host defence under different environmental pathogen pressures. At the same time, it will reveal the shared and unique components of the immunological toolkit and basic functional aspects that are essential for immune defence throughout the living world. In this review, we argue that NGS will revolutionize our understanding of immune responses throughout the animal kingdom because the depth of information it provides will circumvent the need to concentrate on a few "model" species.

Comparative evaluation of haemagglutination potential of haemolymph from two species of giant African land snails (Archachatina marginata and Achatina achatina)

A comparative study was conducted to evaluate haemagglutination potential in the haemolymph of two species of giant African land snails (Archachatina marginata and Achatina achatina). Three liveweight groups of snails (<100 g, 101-150 g and >150 g) were used with 4 replicates per liveweight per species for haemagglutination assay (HA). The effect of aestivation on haemagglutination potential was also evaluated. Erythrocytes (2%) from cattle, sheep, goat and chicken were used for HA assay. Results showed that agglutinin-like substances that agglutinate erythrocytes of sheep, goat, cattle and chicken were present in the haemolymph of the two species of giant African land snails. Effect of species was found to be significant (P < 0.001) on haemagglutination titre. Haemolymph of A. marginata, had higher haemagglutination titre than that of A. achatina across the three liveweight groups used in this study. Snail liveweight had no significant effect (P > 0.05) on agglutinin content of the haemolymph in both species. Agglutination level depended on the source of erythrocyte used. Sheep erythrocyte recorded the highest haemagglutination titre, followed by goat, cattle, and chicken in that order. To our knowledge, this is the first evidence that Giant African land snails (GALS) haemolymph contain agglutinins as previously reported for Helix species. This evidence may be the basis for its survivability in the wild and thus establish the use of GALS for African herbal medicinal applications.

allograft inflammatory factor 1 functions as a pro-inflammatory cytokine in the oyster, Crassostrea ariakensis

The oyster Crassostrea ariakensis is an economically important bivalve species in China, unfortunately it has suffered severe mortalities in recent years caused by rickettsia-like organism (RLO) infection. Prevention and control of this disease is a priority for the development of oyster aquaculture. Allograft inflammatory factor-1 (AIF-1) was identified as a modulator of the immune response during macrophage activation and a key gene in host immune defense reaction and inflammatory response. Therefore we investigated the functions of C. ariakensis AIF-1 (Ca-AIF1) and its antibody (anti-CaAIF1) in oyster RLO/LPS-induced disease and inflammation. Ca-AIF1 encodes a 149 amino acid protein containing two typical Ca2+ binding EF-hand motifs and shares a 48-95% amino acid sequence identity with other animal AIF-1s. Tissue-specific expression analysis indicates that Ca-AIF1 is highly expressed in hemocytes. Significant and continuous up-regulation of Ca-AIF1 is detected when hemocytes are stimulated with RLO/LPS (RLO or LPS). Treatment with recombinant Ca-AIF1 protein significantly up-regulates the expression levels of LITAF, MyD88 and TGFβ. When anti-CaAIF1 antibody is added to RLO/LPS-challenged hemocyte monolayers, a significant reduction of RLO/LPS-induced LITAF is observed at 1.5-12 h after treatment, suggesting that interference with Ca-AIF1 can suppress the inflammatory response. Furthermore, flow cytometric analysis indicated that anti-CaAIF1 administration reduces RLO/LPS-induced apoptosis and necrosis rates of hemocytes. Collectively these findings suggest that Ca-AIF1 functions as a pro-inflammatory cytokine in the oyster immune response and is a potential target for controlling RLO infection and LPS-induced inflammation.

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

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

A shrimp C-type lectin inhibits proliferation of the hemolymph microbiota by maintaining the expression of antimicrobial peptides

Some aquatic invertebrates such as shrimp contain low albeit stable numbers of bacteria in the circulating hemolymph. The proliferation of this hemolymph microbiota in such a nutrient-rich environment is tightly controlled in healthy animals, but the mechanisms responsible had remained elusive. In the present study, we report a C-type lectin (MjHeCL) from the kuruma shrimp (Marsupenaeus japonicus) that participates in restraining the hemolymph microbiota. Although the expression of MjHeCL did not seem to be modulated by bacterial challenge, the down-regulation of its expression by RNA interference led to proliferation of the hemolymph microbiota, ultimately resulting in shrimp death. This phenotype was rescued by the injection of recombinant MjHeCL, which restored the healthy status of the knockdown shrimp. A mechanistic analysis revealed that MjHeCL inhibited bacterial proliferation by modulating the expression of antimicrobial peptides. The key function of MjHeCL in the shrimp immune homeostasis might be related to its broader recognition spectrum of the hemolymph microbiota components than other lectins. Our study demonstrates the role of MjHeCL in maintaining the healthy status of shrimp and provides new insight into the biological significance of C-type lectins, a diversified and abundant lectin family in invertebrate species.

A galectin from the kuruma shrimp (Marsupenaeus japonicus) functions as an opsonin and promotes bacterial clearance from hemolymph

Galectins are a lectin family characterized by a conserved sequence motif in the carbohydrate recognition domain, which preferential binds to galactosyl moieties. However, few studies about the biological roles of galectins in invertebrates have been reported except for the galectin (CvGal1) from the eastern oyster Crassostrea virginica. Furthermore, galectins have been described in only a few crustacean species, and no functional studies have been reported so far. In this study, we identified and functionally characterized a galectin from the kuruma shrimp Marsupenaeus japonicus, which we designated MjGal. Upon Vibrio anguillarum challenge, expression of MjGal was up-regulated mostly in hemocytes and hepatopancreas, and the protein bound to both Gram-positive and Gram-negative bacteria through the recognition of lipoteichoic acid (LTA) or lipopolysaccharide (LPS), respectively. By also binding to the shrimp hemocyte surface, MjGal functions as an opsonin for microbial pathogens, promoting their phagocytosis. Further, as shown by RNA interference, MjGal participates in clearance of bacteria from circulation, and thereby contributes to the shrimp’s immune defense against infectious challenge. Elucidation of functional and mechanistic aspects of shrimp immunity will enable the development of novel strategies for intervention in infectious diseases currently affecting the shrimp farming industry worldwide.