Harnessing the power of mollusc lectins as immuno-protective biomolecules

The rapid advancement of molecular research on macromolecules has contributed to the discovery of 'Lectin', a carbohydrate-binding protein which specifically interacts with receptors on the surface of glycans and regulates various cellular activities thereby stimulating immunological functions. Considering the wide variety of sources and immunological significance, research has led to the discovery of lectins in invertebrate molluscs. Such lectins in molluscs mediate active immune response as they lack adaptive immunity. Phylum Mollusca is identified with different types of lectins such as C-lectin, Galectin, P-lectin, I-lectin, and H-lectin, along with other immunologically significant lectin molecules such as F- lectin, R-lectin, ficolins, chitinase like lectin etc., all of these with specific ligand binding and structural diversity. Molluscan C-type lectins are the most functional ones that increase the activity of phagocytic cells through specific carbohydrate binding of antigenic ligands and haemocyte adhesion thereby enhancing the immune response. Helix pomatia agglutinin and Helix aspersa agglutinin are the two H-lectins that were identified within molluscs that could even target cancer-progressing cells through specific binding. Also, these lectins identified in molluscs are proven to be efficient in antibacterial and immunomodulatory functions. These insights attract researchers to identify novel lectins in molluscs and their characterization that play a key role in protection against diseases. This review discusses the structural features of mollusc lectins, their specific binding, molecular interactions and their immunological applications.

Inhibition of Dopamine Activity and Response of Rhipicephalus microplus Challenged with Metarhizium anisopliae

Dopamine modulates ticks and insect hemocytes and links these arthropods' nervous and immune systems. For the first time, the present study analyzed the effect of a dopamine receptor antagonist on the survival, biological parameters, phagocytic index, and dopamine detection in the hemocytes of ticks challenged by Metarhizium anisopliae. The survival and egg production index of Rhipicephalus microplus were negatively impacted when ticks were inoculated with the antagonist and fungus. Five days after the treatment, the survival of ticks treated only with fungus was 2.2 times higher than ticks treated with the antagonist (highest concentration) and fungus. A reduction in the phagocytic index of hemocytes of 68.4% was observed in the group inoculated with the highest concentration of the antagonist and fungus compared to ticks treated only with fungus. No changes were detected in the R. microplus levels of intrahemocytic dopamine or hemocytic quantification. Our results support the hypothesis that dopamine is crucial for tick immune defense, changing the phagocytic capacity of hemocytes and the susceptibility of ticks to entomopathogenic fungi.

Assessment of Amphora coffeaeformis and Scenedesmus dimorphus algae as immunostimulant agents on Biomphlaria alexandrina snails against Schistosoma mansoni

Schistosoma mansoni is the main factor of human schistosomiasis which is responsible for high rates of mortality. Recently, the use of alternative biological control agents has gained importance in disease control because the intensive use of molluscicides is very harmful to human health and poses risks to the environment. In the present work, the potential effect of two freshwater algae, Amphora coffeaeformis and Scenedesmus obtusus, on the immune response of Biomphalaria alexandrina snails against infection with S. mansoni was investigated. Two different concentrations 1 and 2 g L− 1 from each dried algal material were tested on snails before exposure to miracidial infection by one day. The use of Amphora coffeaeformis has a greater immunostimulatory effect than Scendesmus obtusus at a low concentration of 1.0 g L− 1. The tested algae affected the snail’s hemocytes and its immune response to S. mansoni as evidenced by a significant decrease in infection rate and cercariae production. In addition, increasing in total hemocyte count, the formation of vacuoles, the appearance of several pseudopodia, and the formation of coarse granules in hemocytes of infected snails treated with A. coffeaeformis. Intense tissue reactions were also observed. In conclusion, it was confirmed that these algae can be used as an immunostimulant in the prevention and control of S. mansoni.

Control of vibriosis in shrimp through the management of the microbiota and the immune system

Shrimp aquaculture is constantly threatened by recurrent outbreaks of diseases caused by pathogenic bacteria of the genus Vibrio. Acute hepatopancreatic necrosis disease (AHPND) is one of the most aggressive vibriosis reported to date in the shrimp industry. AHPND provokes massive mortalities, causing economic losses with strong social impacts. Control of vibriosis requires the application of multifactorial strategies. This includes vibrio exclusion, shrimp microbiota, particularly in the digestive tract, and shrimp health management through immune stimulation. This paper reviews these two strategies for the prophylactic control of vibriosis. First, we describe the devastating effects of AHPND and the cellular and humoral effectors of the shrimp immune system to cope with this pathology. Secondly, the mechanisms of action of probiotics and their positive impacts are highlighted, including their immunostimulant effects and their role in the balance of the shrimp microbiota. Finally, we reviewed immunostimulants and prebiotics polysaccharides that together with probiotics act benefiting growth, feed efficiency and the microbiota of the digestive tract of farmed shrimp.

A cellular and molecular atlas reveals the basis of chytrid development

The chytrids (phylum Chytridiomycota) are a major fungal lineage of ecological and evolutionary importance. Despite their importance, many fundamental aspects of chytrid developmental and cell biology remain poorly understood. To address these knowledge gaps, we combined quantitative volume electron microscopy and comparative transcriptome profiling to create an 'atlas' of the cellular and molecular basis of the chytrid life cycle, using the model chytrid Rhizoclosmatium globosum. From our developmental atlas, we describe the transition from the transcriptionally inactive free-swimming zoospore to the more biologically complex germling, and show that lipid processing is multifaceted and dynamic throughout the life cycle. We demonstrate that the chytrid apophysis is a compartmentalised site of high intracellular trafficking, linking the feeding/attaching rhizoids to the reproductive zoosporangium, and constituting division of labour in the chytrid cell plan. We provide evidence that during zoosporogenesis, zoospores display amoeboid morphologies and exhibit endocytotic cargo transport from the interstitial maternal cytoplasm. Taken together, our results reveal insights into chytrid developmental biology and provide a basis for future investigations into non-dikaryan fungal cell biology.

Expanding of Life Strategies in Placozoa: Insights From Long-Term Culturing of Trichoplax and Hoilungia

Placozoans are essential reference species for understanding the origins and evolution of animal organization. However, little is known about their life strategies in natural habitats. Here, by maintaining long-term culturing for four species of Trichoplax and Hoilungia, we extend our knowledge about feeding and reproductive adaptations relevant to the diversity of life forms and immune mechanisms. Three modes of population dynamics depended upon feeding sources, including induction of social behaviors, morphogenesis, and reproductive strategies. In addition to fission, representatives of all species produced “swarmers” (a separate vegetative reproduction stage), which could also be formed from the lower epithelium with greater cell-type diversity. We monitored the formation of specialized spheroid structures from the upper cell layer in aging culture. These “spheres” could be transformed into juvenile animals under favorable conditions. We hypothesize that spheroid structures represent a component of the innate immune defense response with the involvement of fiber cells. Finally, we showed that regeneration could be a part of the adaptive reproductive strategies in placozoans and a unique experimental model for regenerative biology.

Ecological Risks Due to Immunotoxicological Effects on Aquatic Organisms

The immunotoxic effects of some anthropogenic pollutants on aquatic organisms are among the causes of concern over the presence of these pollutants in the marine environment. The immune system is part of an organism's biological defense necessarily for homeostasis. Thus, the immunotoxicological impacts on aquatic organisms are important to understand the effects of pollutant chemicals in the aquatic ecosystem. When aquatic organisms are exposed to pollutant chemicals with immunotoxicity, it results in poor health. In addition, aquatic organisms are exposed to pathogenic bacteria, viruses, parasites, and fungi. Exposure to pollutant chemicals has reportedly caused aquatic organisms to show various immunotoxic symptoms such as histological changes of lymphoid tissue, changes of immune functionality and the distribution of immune cells, and changes in the resistance of organisms to infection by pathogens. Alterations of immune systems by contaminants can therefore lead to the deaths of individual organisms, increase the general risk of infections by pathogens, and probably decrease the populations of some species. This review introduced the immunotoxicological impact of pollutant chemicals in aquatic organisms, including invertebrates, fish, amphibians, and marine mammals; described typical biomarkers used in aquatic immunotoxicological studies; and then, discussed the current issues on ecological risk assessment and how to address ecological risk assessment through immunotoxicology. Moreover, the usefulness of the population growth rate to estimate the immunotoxicological impact of pollution chemicals was proposed.

The effects of cold stress on Mytilus species in the natural environment

Environmental stressors induce changes in marine mussels from molecular (e.g., neurotransmitter and chaperone concentration, and expression of immune- and heat-shock protein-related genes) to physiological (e.g., filtration and heart rates, the number of circulating hemocytes) levels. Temperature directly affects the biogeographic distribution of mussels. Chaperones might form an essential part of endogenous protective mechanisms for the adaptation of these animals to low temperatures in nature. Here, we review the available studies dealing with cold stress responses of Mytilidae family members in their natural environment.

Opsonic character of the plasma proteins in phagocytosis-dependent host response to bacterial infection in a marine invertebrate, Crassostrea gigas

Phagocytosis is an evolutionarily conserved immune response, whose efficiency is fundamentally coupled with opsonization of extracellular microbes. How marine mollusks cells recognize and selectively capture pathogens during phagocytosis to clear them is not completely understood. In this study, we observed that plasma is extremely effective for oyster hemocyte phagocytosis, so we investigated candidate proteins among plasma proteins with binding affinity for Vibrio parahaemolyticus in Pacific oyster (Crassostrea gigas) by subjecting them to mass spectroscopy analysis for protein identification and characterization, and address the complex regulatory network to engulf invaders. There were 620 identified proteins potentially associated with bacteria binding and phagocytosis which could be quantified. Our results showed that C1q and lectins identified in Pacific oyster plasma held binding ability to bacteria, clearly suggesting their potent to be opsonins. The dominant expressed plasma protein p1-CgC1q (Complement component 1q)-like protein was identified and its opsonic role was confirmed in this study. The cell surface receptor Cgintegrin interacts directly with p1-CgC1q to mediate phagocytosis. We further confirmed that the interaction between C1q and integrin not rely on the typical recognition site RGD but on the RGE. Evidence exist revealed that p1-CgC1q could coat bacteria via the endotoxin LPS (lipopolysaccharide) and subsequently bind the receptor integrin to significantly enhance hemocytic phagocytosis and bacteria clearance. This study has thus furnished clear evidence for the importance of plasma proteins in mollusk, shedding light on the humoral immunity and an underappreciated strategy in marine host-pathogen interactions.

Hemocyte phagosomal proteome is dynamically shaped by cytoskeleton remodeling and interorganellar communication with endoplasmic reticulum during phagocytosis in a marine invertebrate, Crassostrea gigas

Phagosomes are task-force organelles of innate immune systems, and evolutionary diversity and continuity abound in the protein machinery executing this coordinately regulated process. In order to clarify molecular mechanisms underlying phagocytosis, we studied phagocyte response to beads and Vibrio species, using hemocytes of the Pacific oysters (Crassostrea gigas) as a marine invertebrate model. Phagosomes from different stages of phagocytosis were isolated by density-gradient centrifugation, and more than 400 phagosome-associated proteins were subsequently identified via high-throughput quantitative proteomics. In modeling key networks of phagosomal proteins, our results support the essential roles of several processes driving phagosome formation and maturation, including cytoskeleton remodeling and signal transduction by Rab proteins. Several endoplasmic reticulum (ER)-associated proteins were identified, while live cell imaging confirms an apparent intimate interaction between the ER and phagosomes. In further quantitative proteomic analysis, the signal transducers CgRhoGDI and CgPI4K were implicated. Through experimental validation, CgRhoGDI was shown to negatively regulate actin cytoskeleton remodeling in the formation of oyster phagosomes, while CgPI4K signaling drives phagosome maturation and bacterial killing. Our current work illustrates the diversity and dynamic interplay of phagosomal proteins, providing a framework for better understanding host-microbe interactions during phagosome activities in under-examined invertebrate species.

Effects of crustacean hyperglycemic hormone (CHH) on regulation of hemocyte intracellular signaling pathways and phagocytosis in white shrimp Litopenaeus vannamei

Shrimps like other arthropods rely on innate immune system, and may have some form of adaptive immunity in defending against pathogens. Phagocytosis is one of the oldest cellular processes, serving as a development process, a feeding mechanism and especially as a key defense reaction in innate immunity of all multicellular organisms. It is confirmed that crustacean hyperglycemic hormone (CHH) is one of the most important neuropeptides produced by Neuro-endocrine Immune (NEI) regulatory network, which undertakes important roles in various biological processes, especially in immune function and stress response. In this study, the recombinant Litopenaeus vannamei CHH (rLvCHH) was obtained from a bacterial expression system and the intracellular signaling pathways involved in the mechanism of phagocytosis after rLvCHH injection was investigated. The results showed that the contents of adenylyl cyclase (AC), phospholipase C (PLC) and calmodulin (CaM) in hemocytes were increased significantly after rLvCHH injection. Furthermore, the mRNA expression levels of NF-kB family members (relish and dorsal) and phagocytosis-related proteins in hemocytes were basically overexpressed after rLvCHH stimulation, while the expression level of NF-kB repressing factor (NKRF) gene was down-regulated significantly. Eventually, the total hemocyte count and phagocytic activity of hemocyte were dramatically enhanced within 3 h. Collectively, these results indicate that shrimps L. vannamei could carry out a simple but 'smart' NEI regulation through the action of neuroendocrine factors, which could couple with their receptors and trigger the downstream signaling pathways during the phagocytic responses of hemocytes.

A non-bilaterian perspective on the development and evolution of animal digestive systems

Digestive systems and extracellular digestion are key animal features, but their emergence during early animal evolution is currently poorly understood. As the last common ancestor of non-bilaterian animal groups (sponges, ctenophores, placozoans and cnidarians) dates back to the beginning of animal life, their study and comparison provides important insights into the early evolution of digestive systems and functions. Here, I have compiled an overview of the development and cell biology of digestive tissues in non-bilaterian animals. I will highlight the fundamental differences between extracellular and intracellular digestive processes, and how these are distributed among animals. Cnidarians (e.g. sea anemones, corals, jellyfish), the phylogenetic outgroup of bilaterians (e.g. vertebrates, flies, annelids), occupy a key position to reconstruct the evolution of bilaterian gut evolution. A major focus will therefore lie on the development and cell biology of digestive tissues in cnidarians, especially sea anemones, and how they compare to bilaterian gut tissues. In that context, I will also review how a recent study on the gastrula fate map of the sea anemone Nematostella vectensis challenges our long-standing conceptions on the evolution of cnidarian and bilaterian germ layers and guts.

Dynamic of small polyethylene microplastics (≤10 μm) in mussel's tissues

MPs' uptake and tissue accumulation were investigated in mussel exposed to a single dose (2.85 mg ind^-1, 3 mg l^-1) of a heterogeneous mixture of irregularly shaped particles of HDPE (mainly ≤10 μm), followed by a 7 days depuration period. The results showed that mussels efficiently cleared MPs from water during exposure, and that MPs were accumulated in digestive gland and gills during depuration. In digestive gland, the amount and size of the MPs accumulated decreased with time, indicating a slower processing and elimination of small MPs than of larger ones. In gills, MPs' burdens increased with time, the MPs accumulated were the smallest ones, suggesting the translocation of small MPs from the digestive system to the gills. The hazardous potential of the smaller fraction of MPs (≤4 μm) underlined that more focus should be directed towards the accumulation and effects of this fraction of MPs in the marine environment.

Responses of marine mussel Mytilus galloprovincialis (Bivalvia: Mytilidae) after infection with the pathogen Vibrio splendidus

Bivalve molluscs possess effective cellular and humoral defence mechanisms against bacterial infection. Although the immune responses of mussels to challenge with pathogenic vibrios have been largely investigated, the effects at the site of injection at the tissue level have not been so far evaluated. To this aim, mussels Mytilus galloprovincialis were herein in vivo challenged with Vibrio splendidus to assess the responses induced in hemolymph and posterior adductor muscle (PAM), being the site of bacterial infection. The number of living intra-hemocyte bacteria increased after the first hour post-injection (p.i.), suggesting the occurrence of an intense phagocytosis, while clearance was observed within 24 h p.i. A recruitment of hemocytes at the injection site was found in mussel PAM, together with marked morphological changes in the volume of muscular fibers, with a recovery of muscle tissue organization after 48 h p.i. A concomitant impairment in the osmoregulatory processes were observed in PAM by an initial inhibition of aquaporins and increased immunopositivity of Na⁺/K⁺ ATPase ionic pump, strictly related to the histological alterations and hemocyte infiltration detected in PAM. Accordingly, an intense cell turnover activity was also recorded following the infection event. Overall, results indicated the hemolymph as the system responsible for the physiological adaptations in mussels to stressful factors, such as pathogenicity, for the maintenance of homeostasis and immune defence. Also, the osmotic balance and cell turnover can be used as objective diagnostic criteria to evaluate the physiological state of mussels following bacterial infection, which may be relevant in aquaculture and biomonitoring studies.

One recombinant C-type lectin (LvLec) from white shrimp Litopenaeus vannamei affected the haemocyte immune response in vitro

C-type lectin has received widespread attention in animal immunomodulation functions since it was discovered, but it is still limited in crustaceans. The present study is to explore effects of one recombinant C-type lectin (LvLec protein) on haemocyte immune response in Litopenaeus vannamei (L. vannamei). The methods of keeping haemocyte immune activity were optimised by the Key Laboratory of Mariculture. The experiment was divided into four groups: control group, recombinant protein group (LvLec protein, 1.0 mg mL^-1), Lipopolysaccharide group (LPS, 1.0 mg mL^-1), and LPS combine with LvLec protein group (LPS + LvLec protein, 1.0 mg mL^-1 + 1.0 mg mL^-1), while each group processes 0, 3, 6, 9, 12, and 24 h respectively. The results showed that the haemocyte count reduced, while the exocytosis PO activity, hemagglutinating activity and phagocytic activity promoted, and the concentration of cGMP and PKA increased after LvLec protein treatment. However, the levels of antibacterial activity and bacteriolytic activity as well as the concentrations of cAMP and PKG did not change significantly after treating with LvLec protein, LPS or LPS + LvLec protein. Therefore, these results suggest that LvLec protein can stimulate the exocytosis PO activity through cGMP-PKA pathway to affect the phagocytic activity and hemagglutinating activity of L. vannamei haemocytes in vitro.

Ultrastructural and Cytotoxic Effects of Metarhizium robertsii Infection on Rhipicephalus microplus Hemocytes

Metarhizium is an entomopathogenic fungus widely employed in the biological control of arthropods. Hemocytes present in the hemolymph of invertebrates are the cells involved in the immune response of arthropods. Despite this, knowledge about Rhipicephalus microplus hemocytes morphological aspects as well as their role in response to the fungal infection is scarce. The present study aimed to analyze the hemocytes of R. microplus females after Metarhizium robertsii infection, using light and electron microscopy approaches associated with the cytotoxicity evaluation. Five types of hemocytes (prohemocytes, spherulocytes, plasmatocytes, granulocytes, and oenocytoids) were described in the hemolymph of uninfected ticks, while only prohemocytes, granulocytes, and plasmatocytes were observed in fungus-infected tick females. Twenty-four hours after the fungal infection, only granulocytes and plasmatocytes were detected in the transmission electron microscopy analysis. Hemocytes from fungus-infected tick females showed several cytoplasmic vacuoles with different electron densities, and lipid droplets in close contact to low electron density vacuoles, as well as the formation of autophagosomes and subcellular material in different stages of degradation could also be observed. M. robertsii propagules were more toxic to tick hemocytes in the highest concentration tested (1.0 × 108 conidia mL-1). Interestingly, the lowest fungus concentration did not affect significantly the cell viability. Microanalysis showed that cells granules from fungus-infected and uninfected ticks had similar composition. This study addressed the first report of fungal cytotoxicity analyzing ultrastructural effects on hemocytes of R. microplus infected with entomopathogenic fungi. These results open new perspectives for the comprehension of ticks physiology and pathology, allowing the identification of new targets for the biological control.

Transcriptome analysis and discovery of genes involved in immune pathways in Solen strictus (Gould, 1861) under Vibrio anguillarum

The Solen strictus (Gould, 1861) has been recognized as an important marine economic bivalve in Eastern and Southeast Asia. To gain a better understanding of the S. strictus immune system and its related genes in response to bacterial infections, we performed a comparative gene transcription analysis from S. strictus with Vibrio anguillarum through RNA-Seq technology, meanwhile the differentially expressed genes (DEGs) were investigated. After assembly, a total of 195,774 transcripts with an average length of 996 bp were obtained. Total 153,038 unigenes were annotated in the nr, Swiss-Prot, KEGG, COG, KOG, GO and Pfam databases, and 56,597 unigenes (36.98%) were annotated in at least one database. After bacterial challenge, there were 1588 significant differentially expressed genes (DEGs) between the challenged and control groups, including 999 up-regulated and 589 down-regulated genes. All the DEGs were classified into three gene ontology categories, and allocated to 225 KEGG pathways. Immune-related genes were detected from immune system pathways among the top 20 enriched pathways, such as Toll-like receptor signaling, RIG-I-like receptor signaling and NOD-like receptor signaling pathway. In addition, 56,079 potential simple sequence repeats (SSRs) and 1,031,521 candidate single nucleotide polymorphisms (SNPs) were detected and identified in the S. strictus transcriptome. Results of the present study will provide valuable theoretical resources for future genetic and genomic research on S. strictus. The research results will be helpful for improving the efficiency and quality of artificial breeding, establishing genetic linkage map, and enhancing health management for this species.

Flow cytometry and micro-Raman spectroscopy: Identification of hemocyte populations in the mussel Mytilus galloprovincialis (Bivalvia: Mytilidae) from Faro Lake and Tyrrhenian Sea (Sicily, Italy)

Immunological and structural characteristics of hemocyte populations in the mussel Mytilus galloprovincialis (Bivalvia: Mytilidae), going from two different Sicilian habitats (Faro Lake and Tyrrhenian sea), was investigated by means of two different techniques (flow cytometric and micro-Raman spectroscopy analyses). For this purpose, three hundred and sixty mussels Mytilus galloprovincialis were analyzed during November 2017. They were divided into two equal groups (triplicate sample) on the basis of the site of collection (n = 60 caught in Faro Lake - group A, and n = 60 caught in Tyrrhenian Sea - group B). Some several differences between the species of Faro Lake and Tyrrhenian Sea are observed and ascribed to the disruption of immune parameters induced by the variations of some qualitative water parameters (temperature, salinity, dissolved oxygen, pH, ammonium 10, free chlorine, total chlorine, total phosphate, orthofhosphate) recorded in the two habitats. This study is relevant for monitoring the conditions of the sea and Faro Lake, which is strongly influenced by the currents of the Tyrrhenian Sea. Faro lake is well known for the cultivation of mussels and this is part of a coastal habitat of particular interest, consisted of a peculiar biocenotic complex. Further, for the first time, significant different arrangement in the mussels cell structural organization was evidenced by simply following their highly reproducible Raman biomolecular signatures.

Comparative study of β-thymosin in two scallop species Argopecten irradians and Chlamys farreri

The β-thymosin (Tβ) proteins participate in numerous biological processes, such as cell proliferation and differentiation, anti-inflammatory and antimicrobial mechanism. To date, Tβ proteins have been well studied in vertebrates, especially mammals. While limited Tβ or Tβ-like proteins have been reported in invertebrates. Moreover, rare information of Tβ or Tβ-like proteins is available in scallop species yet. In the present study, two Tβ homologues, AiTβ and CfTβ, were identified and characterized from two scallop species bay scallop Argopecten irradians and Zhikong scallop Chlamys farreri. They were both 41 amino acid peptide and contained one THY domain, a highly conserved actin-binding motif and two conserved helix forming regions. Tissue distribution and expression profiles of their mRNA transcripts were roughly similar yet different in detail, while their recombinant proteins exhibited different immunomodulation activity on the downstream immune parameters. These results collectively indicated that the function of Tβ family in scallop were functionally differentiated.

Transcriptome analysis of the Yesso scallop, Patinopecten yessoensis gills in response to water temperature fluctuations

Water temperature fluctuations are considered to be a major factor affecting the immune functions and metabolic processes of scallops. To better understand the immune defense mechanisms of Yesso scallop, Patinopecten yessoensis following exposure to water temperature fluctuations, transcriptomic profiles in the gills from high-frequency fluctuations (HF_G), low-frequency fluctuations (LF_G), and no fluctuations (NF_G) groups were obtained using HiSeq™ 2500 (Illumina). For HF_G, scallops were transferred directly between 18 and 8 °C every 4 h and for 10 fluctuations, while scallops in LF_G were transferred between 18 and 13 °C every 12 h, for a total of 4 fluctuations. A total of 442,922,590 clean reads were generated in 9 libraries and then assembled into 210,780 unigenes with an average length of 705 bp and an N50 of 1253 bp. Based on sequence similarity, 54,529 unigenes (25.87%) were annotated in at least one database. Comparative analysis revealed that 696 unigenes differentially expressed in temperature stressed groups compared with the control, including 229 unigenes between HF_G and NF_G, and 548 unigenes between LF_G and NF_G, respectively. Additionally, among these differentially expressed genes (DEGs), there were 41 immune-related unigenes and 16 protein metabolism-related unigenes. These results provide fundamental information on the molecular defense mechanisms in the Yesso scallop gills after exposure to water temperature fluctuations.

Endogenous molecules released by haemocytes receiving Sargassum oligocystum extract lead to downstream activation and synergize innate immunity in white shrimp Litopenaeus vannamei

White shrimp Litopenaeus vannamei haemocytes receiving immunostimulating Sargassum oligocystum extract (SE) caused necrosis in haemocyte cells, which released endogenous EM-SE molecules. This study examined the immune response of white shrimp L. vannamei receiving SE and EM-SE in vitro and in vivo. Shrimp haemocytes receiving SE exhibited degranulation, changes in cell size and cell viability, necrosis and a release of EM-SE. Shrimp haemocytes receiving SE, EM-SE, and the SE + EM-SE mixture (SE + EM-SE) increased their phenoloxidase (PO) activity which was significantly higher in shrimp haemocytes receiving the SE + EM-SE mixture. Furthermore, shrimp haemocytes receiving EM-SE showed degranulation and changes in cell size and cell viability. Shrimp receiving SE, EM-SE, and SE + EM-SE all increased their immune parameters, phagocytic activity, clearance efficiency and resistance to Vibrio alginolyticus, being significantly higher in shrimp receiving SE + EM-SE. Meanwhile, the recombinant lipopolysaccharide- and β-1,3-glucan binding protein of L. vannamei (rLvLGBP) was bound to SE, EM-SE, and SE + EM-SE. We conclude that in shrimp haemocytes receiving a non-self molecule, SE in dying cells released EM-SE which led to downstream activation and synergization of the immune response. This study demonstrated that the innate immunity of shrimp was elicited and enhanced by a mixture of endogenous molecules and exogenous substances (or immunostimulants).

Metatranscriptomics profile of the gill microbial community during Bathymodiolus azoricus aquarium acclimatization at atmospheric pressure

Background

The deep-sea mussels Bathymodiolus azoricus (Bivalvia: Mytilidae) are the dominant macrofauna subsisting at the hydrothermal vents site Menez Gwen in the Mid-Atlantic Ridge (MAR). Their adaptive success in such challenging environments is largely due to their gill symbiotic association with chemosynthetic bacteria. We examined the response of vent mussels as they adapt to sea-level environmental conditions, through an assessment of the relative abundance of host-symbiont related RNA transcripts to better understand how the gill microbiome may drive host-symbiont interactions in vent mussels during hypothetical venting inactivity.

Results

The metatranscriptome of B. azoricus was sequenced from gill tissues sampled at different time-points during a five-week acclimatization experiment, using Next-Generation-Sequencing. After Illumina sequencing, a total of 181,985,262 paired-end reads of 150 bp were generated with an average of 16,544,115 read per sample. Metatranscriptome analysis confirmed that experimental acclimatization in aquaria accounted for global gill transcript variation. Additionally, the analysis of 16S and 18S rRNA sequences data allowed for a comprehensive characterization of host-symbiont interactions, which included the gradual loss of gill endosymbionts and signaling pathways, associated with stress responses and energy metabolism, under experimental acclimatization. Dominant active transcripts were assigned to the following KEGG categories: “Ribosome”, “Oxidative phosphorylation” and “Chaperones and folding catalysts” suggesting specific metabolic responses to physiological adaptations in aquarium environment.

Conclusions

Gill metagenomics analyses highlighted microbial diversity shifts and a clear pattern of varying mRNA transcript abundancies and expression during acclimatization to aquarium conditions which indicate change in bacterial community activity. This approach holds potential for the discovery of new host-symbiont associations, evidencing new functional transcripts and a clearer picture of methane metabolism during loss of endosymbionts. Towards the end of acclimatization, we observed trends in three major functional subsystems, as evidenced by an increment of transcripts related to genetic information processes; the decrease of chaperone and folding catalysts and oxidative phosphorylation transcripts; but no change in transcripts of gluconeogenesis and co-factors-vitamins.

Hybridization improved bacteria resistance in abalone: Evidence from physiological and molecular responses

Hybridization is an effective way of improving germplasm in abalone, as it often generates benign traits in the hybrids. The hybrids of Haliotis discus hannai and H. gigantea have shown heterosis in terms of disease resistance than one or both parental species. In the present study, to elucidate the physiological and molecular mechanism of this heterosis, we analyzed the dynamic changes of several immune indexes including survival rate, total circulating haemocyte count (THC), phagocytic activity, reactive oxygen species level (ROS) and phenoloxidase activity (PO) in two parental species, H. discus hannai (DD) and H. gigantea (GG), and their reciprocal hybrids H. discus hannai ♀ × H. gigantea ♂ (DG), H. gigantea ♀ × H. discus hannai ♂ (GD) challenged with a mixture of Vibrio harveyi, V. alginolyticus and V. parahaemolyticus (which have been demonstrated to be pathogenic to abalone). Besides, we cloned and analyzed three important immune genes: heat shock protein 70 (hsp70), ferritin and cold shock domain protein (csdp) in H. discus hannai and H. gigantea, then further investigated their mRNA level changes in the four abalone genotypes after bacterial challenge. Results showed that these physiological and molecular parameters were significantly induced by bacterial exposure, and their changing patterns were obviously different between the four genotypes: (1) Survival rates of the two hybrids were higher than both parental species after bacterial exposure; (2) DG had higher THC than the other three genotypes; (3) Phagocytosis responded slower in the hybrids than in the parental species; (4) DD's ROS level was lower than the other three genotypes at 48 h post infection; (5) Phenoloxidase activity was lower in DD during the infection compared to the other genotypes; (6) mRNA levels of hsp70 and csdp, were always lower in at least one parental species (DD) than in the hybrids after the bacterial exposure. Results from this study indicate that the hybrids are more active or efficient in immune system function, hence they could effectively defense against a bacterial invasion, leading to higher survival rates after challenge. This study provides physiological and molecular evidences for interpreting the disease resistant heterosis in this abalone hybrid system, which could help us in a better understanding and utilization of heterosis in abalone aquaculture.

Carbohydrate Moieties and Cytoenzymatic Characterization of Hemocytes in Whiteleg Shrimp Litopenaeus vannamei

Hemocytes represent one of the most important defense mechanisms against foreign material in Crustacea and are also involved in a variety of other physiological responses. Fluorescent lectin-binding assays and cytochemical reactions were used to identify specificity and distribution of carbohydrate moieties and presence of several hydrolytic enzymes, in hemocytes of whiteleg shrimp Litopenaeus vannamei. Two general classes of circulating hemocytes (granular and agranular) exist in L. vannamei, which express carbohydrates residues for FITC-conjugated lectins WGA, LEA, and PNA; UEA and Con-A were not observed. Enzymatic studies indicated that acid phosphatase, nonspecific esterase, and specific esterases were present; alkaline phosphatase was not observed. The enzymes and carbohydrates are useful tools in hemocyte classification and cellular defense mechanism studies.

Combined effects of seawater acidification and high temperature on hemocyte parameters in the thick shell mussel Mytilus coruscus

In this work, flow cytometry was used to examine the immune responses of hemocytes in the thick shell mussel Mytilus coruscus exposed to six combinations of pH (7.3, 7.7, and 8.1) and temperature (25 °C and 30 °C) for 14 days. Temperature showed significant effects on all immune parameters throughout the experiment. Generally, the total hemocyte count (THC), phagocytosis (Pha), esterase (Est), and lysosomal content (Lyso) significantly decreased at high temperature. By contrast, the hemocyte mortality (Hm) and reactive oxygen species (ROS) levels increased at high temperature. Moreover, pH significantly influenced all the immune parameters, but its effects are not as strong as those of temperature; only Hm, Est, and THC were negatively affected by pH throughout the experiment. After 7 days, low pH resulted in decreased Lyso and increased Hm and ROS levels. Significant interactions between temperature and pH in most measured parameters from 7 days suggested that long-term combined stress, i.e., low pH and high temperature, would cause more severe effects on mussel health than an individual stressor in the field.

The known two types of transglutaminases regulate immune and stress responses in white shrimp, Litopenaeus vannamei

Transglutaminases (TGs) play critical roles in blood coagulation, immune responses, and other biochemical functions, which undergo post-translational remodeling such as acetylation, phosphorylation and fatty acylation. Two types of TG have been identified in white shrimp, Litopenaeus vannamei, and further investigation on their potential function was conducted by gene silencing in the present study. Total haemocyte count (THC), differential haemocyte count (DHC), phenoloxidase activity, respiratory bursts (release of superoxide anion), superoxide dismutase activity, transglutaminase (TG) activity, haemolymph clotting time, and phagocytic activity and clearance efficiency to the pathogen Vibrio alginolyticus were measured when shrimps were individually injected with diethyl pyrocarbonate-water (DEPC-H2O) or TG dsRNAs. In addition, haemolymph glucose and lactate, and haemocytes crustin, lysozyme, crustacean hyperglycemic hormone (CHH), transglutaminaseI (TGI), transglutaminaseII (TGII) and clotting protein (CP) mRNA expression were determined in the dsRNA injected shrimp under hypothermal stress. Results showed that TG activity, phagocytic activity and clearance efficiency were significantly decreased, but THC, hyaline cells (HCs) and haemolymph clotting time were significantly increased in the shrimp which received LvTGI dsRNA and LvTGI + LvTGII dsRNA after 3 days. However, respiratory burst per haemocyte was significantly decreased in only LvTGI + LvTGII silenced shrimp. In hypothermal stress studies, elevation of haemolymph glucose and lactate was observed in all treated groups, and were advanced in LvTGI and LvTGI + LvTGII silenced shrimp following exposure to 22 °C. LvCHH mRNA expression was significantly up-regulated, but crustin and lysozyme mRNA expressions were significantly down-regulated in LvTGI and LvTGI + LvTGII silenced shrimp; moreover, LvTGII was significantly increased, but LvTGI was significantly decreased in LvTGI silenced shrimp following exposure to 28 and 22 °C. Knockdown of LvTGI and LvTGI + LvTGII also significantly increased the mortality of L. vannamei challenged with the pathogen V. alginolyticus. The same consequences have been confirmed in LvTGII silenced shrimp in our previous study. These results indicate that LvTGI and LvTGII not only reveal a complementary effect in gene expression levels but also play a key function in the immune defence mechanism of shrimp, by regulating the haemolymph coagulation, immune parameters and immune related gene expression, and in the regulation of carbohydrate metabolism.

First evidence for a Vibrio strain pathogenic to Mytilus edulis altering hemocyte immune capacities

Bacterial isolates were obtained from mortality events affecting Mytilus edulis and reported by professionals in 2010-2013 or from mussel microflora. Experimental infections allowed the selection of two isolates affiliated to Vibrio splendidus/Vibrio hemicentroti type strains: a virulent 10/068 1T1 (76.6% and 90% mortalities in 24 h and 96 h) and an innocuous 12/056 M24T1 (0% and 23.3% in 24 h and 96 h). These two strains were GFP-tagged and validated for their growth characteristics and virulence as genuine models for exposure. Then, host cellular immune responses to the microbial invaders were assessed. In the presence of the virulent strain, hemocyte motility was instantaneously enhanced but markedly slowed down after 2 h exposure. By contrast, hemocyte velocity increased in the presence of the innocuous 12/056 M24T1. At the same time interval, 10/068 1T1 invaded hemocytes and was more rapidly internalized than the innocuous strain. Extracellular products (ECPs) prepared from 10/068 1T1 cultures significantly inhibited phagocytic activity while 12/056 M24T1 ECPs had no effect. Furthermore, the pathogenic strain and its ECPs inhibited oxidative burst unlike 12/056 M24T1 strain/ECPs which enhanced ROS production. Taken together, our results suggest that the mussel pathogen 10/068 1T1 may escape immune response by altering hemocytes functions.

Clam focal and systemic immune responses to QPX infection revealed by RNA-seq technology

Background

The hard clam Mercenaria mercenaria is an important seafood species widely exploited along the eastern coasts of the United States and play a crucial role in coastal ecology and economy. Severe hard clam mortalities have been associated with the protistan parasite QPX (Quahog Parasite Unknown). QPX infection establishes in pallial organs with the lesions typically characterized as nodules, which represent inflammatory masses formed by hemocyte infiltration and encapsulation of parasites. QPX infection is known to induce host changes on both the whole-organism level and at specific lesion areas, which imply systemic and focal defense responses, respectively. However, little is known about the molecular mechanisms underlying these alterations.

Results

RNA-seq was performed using Illumina Hiseq 2000 (641 Million 100 bp reads) to characterize M. mercenaria focal and systemic immune responses to QPX. Transcripts were assembled and the expression levels were compared between nodule and healthy tissues from infected clams, and between these and tissues from healthy clams. De novo assembly reconstructed a consensus transcriptome of 62,980 sequences that was functionally-annotated. A total of 3,131 transcripts were identified as differentially expressed in different tissues. Results allowed the identification of host immune factors implicated in the systemic and focal responses against QPX and unraveled the pathways involved in parasite neutralization. Among transcripts significantly modulated upon host-pathogen interactions, those involved in non-self recognition, signal transduction and defense response were over-represented. Alterations in pathways regulating hemocyte focal adhesion, migration and apoptosis were also demonstrated.

Conclusions

Our study is the first attempt to thoroughly characterize M. mercenaria transcriptome and identify molecular features associated with QPX infection. It is also one of the first studies contrasting focal and systemic responses to infections in invertebrates using high-throughput sequencing. Results identified the molecular signatures of clam systemic and focal defense responses, to collectively mediate immune processes such as hemocyte recruitment and local inflammation. These investigations improve our understanding of bivalve immunity and provide molecular targets for probing the biological bases of clam resistance towards QPX.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2493-9) contains supplementary material, which is available to authorized users.

Activation of immunity, immune response, antioxidant ability, and resistance against Vibrio alginolyticus in white shrimp Litopenaeus vannamei decrease under long-term culture at low pH

The growth, activation of immunity, immune parameters, and transcript levels of cytMnSOD, mtMnSOD, ecCuZnSOD, glutathione peroxidase (GPx), catalase, lysozyme, and penaeidin 3a were examined in white shrimp Litopenaeus vannamei reared at pH 6.8 and 8.1 after 24 weeks. No significant difference in growth was observed between the two groups. An in vitro study indicated that phenoloxidase activity and respiratory bursts (RB, release of the superoxide anion) were significantly higher in the haemocytes of pH 8.1 shrimp (shrimp reared at pH 8.1) than in pH 6.8 shrimp (shrimp reared at pH 6.8). An in vivo study indicated that the levels of immune parameters of pH 8.1 shrimp were significantly higher than in pH 6.8 shrimp, and the transcript levels of cytMnSOD, ecCuZnSOD, glutathione peroxidase, lysozyme, and penaeidin 3a were down-regulated in pH 6.8 shrimp. In another experiment, shrimp reared at pH 6.8 and 8.1 for 24 weeks were challenged with Vibrio alginolyticus. The mortality rate of pH 6.8 shrimp was significantly higher than in pH 8.1 shrimp over 12-168 h. Phagocytic activity, phagocytic index, and clearance efficiency to V. alginolyticus were significantly lower in pH 6.8 shrimp. We concluded that shrimp under long-term culture at pH 6.8 exhibited decreased resistance against V. alginolyticus as evidenced by reductions in the activation of immunity and immune parameters together with decreased transcript levels of cytMnSOD, ecCuZnSOD, GPx, lysozyme, and penaeidin 3a.

Effects of waterborne nickel on the physiological and immunological parameters of the Pacific abalone Haliotis discus hannai during thermal stress

In this study, the 96-h LC50 at 22 and 26 °C values was 28.591 and 11.761 mg/L, respectively, for NiCl2 exposure in the abalone. The alteration of physiological and immune-toxicological parameters such as the total hemocyte count (THC), lysozyme, phenoloxidase (PO), and phagocytosis activity was measured in the abalone exposed to nickel (200 and 400 μg/L) under thermal stress for 96 h. In this study, Mg and THC decreased, while Ca, lysozyme, PO, and phagocytosis activity increased in the hemolymph of Pacific abalone exposed to NiCl2 when compared to a control at both 22 and 26 °C. However, these parameters were not affected by a rise in temperature from 22 to 26 °C in non-exposed groups. Our results showed that NiCl2 below 400 μg/L was able to stimulate immune responses in abalone. However, complex stressors, thermal changes, or NiCl2 can modify the immunological response and lead to changes in the physiology of host-pollutant interactions in the abalone.

The early stages of the immune response of the European abalone Haliotis tuberculata to a Vibrio harveyi infection

Vibrio harveyi is a marine bacterial pathogen responsible for episodic abalone mortalities in France, Japan and Australia. In the European abalone, V. harveyi invades the circulatory system in a few hours after exposure and is lethal after 2 days of infection. In this study, we investigated the responses of European abalone immune cells over the first 24 h of infection. Results revealed an initial induction of immune gene expression including Rel/NF-kB, Mpeg and Clathrin. It is rapidly followed by a significant immuno-suppression characterized by reduced cellular hemocyte parameters, immune response gene expressions and enzymatic activities. Interestingly, Ferritin was overexpressed after 24 h of infection suggesting that abalone attempt to counter V. harveyi infection using soluble effectors. Immune function alteration was positively correlated with V. harveyi concentration. This study provides the evidence that V. harveyi has a hemolytic activity and an immuno-suppressive effect in the European abalone.

Phagocytic activities of hemocytes from the deep-sea symbiotic mussels Bathymodiolus japonicus, B. platifrons, and B. septemdierum

Deep-sea mytilid mussels harbor symbiotic bacteria in their gill epithelial cells that are horizontally or environmentally transmitted to the next generation of hosts. To understand the immune defense system in deep-sea symbiotic mussels, we examined the hemocyte populations of the symbiotic Bathymodiolus mussel species Bathymodiolus japonicus, Bathymodiolus platifrons, and Bathymodiolus septemdierum, and characterized three types of hemocytes: agranulocytes (AGs), basophilic granulocytes (BGs), and eosinophilic granulocytes (EGs). Of these, the EG cells were the largest (diameter, 8.4-10.0 μm) and had eosinophilic cytoplasm with numerous eosinophilic granules (diameter, 0.8-1.2 μm). Meanwhile, the BGs were of medium size (diameter, 6.7-8.0 μm) and contained small basophilic granules (diameter, 0.3-0.4 μm) in basophilic cytoplasm, and the AGs, the smallest of the hemocytes (diameter, 4.8-6.0 μm), had basophilic cytoplasm lacking granules. A lectin binding assay revealed that concanavalin A bound to all three hemocyte types, while wheat germ agglutinin bound exclusively to EGs and BGs. The total hemocyte population densities within the hemolymph of all three Bathymodiolus mussel species were similar (8.4-13.3 × 10(5) cells/mL), and the percentages of circulating AGs, BGs, and EGs in the hemolymph of these organisms were 44.7-48.5%, 14.3-17.6%, and 34.3-41.0%, respectively. To analyze the functional differences between these hemocytes, the phagocytic activity and post-phagocytic phagosome-lysosome fusion events were analyzed in each cell type using a fluorescent Alexa Fluor(®) 488-conjugated Escherichia coli bioparticle and a LysoTracker(®) lysosomal marker, respectively. While the AGs exhibited no phagocytic activity, both types of granulocytes were phagocytic. Of the three hemocyte types, the EGs exhibited the highest level of phagocytic activity as well as rapid phagosome-lysosome fusion, which occurred within 2 h of incubation. Meanwhile, the BGs showed lower phagocytic activity and lower rates of phagosome-lysosome fusion than the EGs. These findings indicate that the two types of granulocyte play distinct roles in the defense system.

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

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

LvDJ-1 plays an important role in resistance against Vibrio alginolyticus in Litopenaeus vannamei

DJ-1 was first identified as an oncogene that transformed mouse NIH3T3 cells in cooperation with activated Ras. It has since exhibited a variety of functions in a range of organisms. In this study, the DJ-1 gene in Litopenaeus vannamei (LvDJ-1) was identified and characterized. A recombinant protein LvDJ-1 was produced in Pichia pastoris. LvDJ-1 expression in vivo was knocked down by dsRNA-mediated RNA interference (RNAi), which led to significantly decreased levels of LvDJ-1 mRNA and protein. When the L. vannamei were challenged with RNAi and Vibrio alginolyticus, the transcription and expression of copper zinc superoxide dismutase (LvCZSOD) in the hepatopancreas were dramatically lower in shrimp with knocked down LvDJ-1 than in controls. Transcription and expression of P53 (LvP53) were significantly higher in shrimp lacking LvDJ-1 than in controls. Hepatopancreas samples were analyzed using real time polymerase chain reaction and Western blot. Moreover, blood samples from the shrimp, assessed with flow cytometry, showed significant increases in respiratory burst and apoptosis in those lacking LvDJ-1 compared to the controls. Cumulative mortality in the shrimp lacking LvDJ-1 was significantly different from that in the control group after challenge with V. alginolyticus. Altogether, the results prove that LvDJ-1 regulates apoptosis and antioxidant activity, and that these functions play an important role in L. vannamei resistance against V. alginolyticus.

A modified method to detect the phagocytic ability of eosinophilic and basophilic haemocytes in the oyster Crassostrea plicatula

The immune defence system of bivalve species largely depends on haemocytes. Haemocytes are generally classified as hyalinocytes (H) or granulocytes (G), and each cell type is further sub-classified as eosinophilic (E) or basophilic (B) haemocytes. Until recently, research on eosinophilic and basophilic haemocytes has primarily focused on their morphologies, dye affinities and intracellular components. Few studies have investigated their phagocytic ability because of the absence of appropriate experimental methods. In this study, we introduce a modified method suitable to detect the phagocytic ability of eosinophilic and basophilic haemocytes. This modified method involves neutral red staining by employing fluorescent microspheres as the phagocytosed medium. Specifically, haemocytes are incubated with fluorescent microspheres and then stained with neutral red. Next, the stained haemocytes are fixed by acetone and are counterstained by propidium iodide. Finally, the haemocytes are observed under a multifunctional microscope to analyse the phagocytic ability by counting the number of eosinophilic or basophilic haemocytes involved in phagocytosis (calculation for phagocytic rate, PR) and the number of phagocytosed microspheres by each eosinophilic or basophilic haemocyte (calculation for phagocytic index, PI). By employing this modified method in the oyster Crassostrea plicatula, we found that the PRs of G and H were very similar to the data obtained by another method, flow cytometry, indicating that this modified method has high accuracy. Additionally, we also found that the PR and PI in E-G were 70.9 ± 7.3% and 1.0 ± 0.2, respectively, which were both significantly higher than those in B-G (53.1 ± 6.4% and 0.7 ± 0.1). The PR and PI in E-H were 16.3 ± 2.8% and 0.2 ± 0.1, respectively, while in B-H, the PR and PI were 13.3 ± 3.6% and 0.2 ± 0.1, respectively, with no significant difference observed. Based on this result, eosinophilic granulocytes are more active in phagocytosis than basophilic granulocytes in the oyster immune defence system.

Adult somatic progenitor cells and hematopoiesis in oysters

Long-lived animals show a non-observable age-related decline in immune defense, which is provided by blood cells that derive from self-renewing stem cells. The oldest living animals are bivalves. Yet, the origin of hemocytes, the cells involved in innate immunity, is unknown in bivalves and current knowledge about mollusk adult somatic stem cells is scarce. Here we identify a population of adult somatic precursor cells and show their differentiation into hemocytes. Oyster gill contains an as yet unreported irregularly folded structure (IFS) with stem-like cells bathing into the hemolymph. BrdU labeling revealed that the stem-like cells in the gill epithelium and in the nearby hemolymph replicate DNA. Proliferation of this cell population was further evidenced by phosphorylated-histone H3 mitotic staining. Finally, these small cells, most abundant in the IFS epithelium, were found to be positive for the stemness marker Sox2. We provide evidence for hematopoiesis by showing that co-expression of Sox2 and Cu/Zn superoxide dismutase, a hemocyte-specific enzyme, does not occur in the gill epithelial cells but rather in the underlying tissues and vessels. We further confirm the hematopoietic features of these cells by the detection of Filamin, a protein specific for a sub-population of hemocytes, in large BrdU-labeled cells bathing into gill vessels. Altogether, our data show that progenitor cells differentiate into hemocytes in the gill, which suggests that hematopoiesis occurs in oyster gills.

Phagocytosis and respiratory burst activity of haemocytes from the ivory snail, Babylonia areolata

Haemocytes from the ivory snail, Babylonia areolata phagocytized Saccharomyces cerevisiae and Vibrio parahaemolyticus after 30 min. Haemocytes phagocytized V. parahaemolyticus at a greater rate than they phagocytized S. cerevisiae. The phagocytic rate (PP) of V. parahaemolyticus by granulocytes to was a little higher than that of S. cerevisiae. The phagocytic index (PI) of V. parahaemolyticus by granulocytes was significantly higher than that of S. cerevisiae. The same was true of hyalinocytes. The PP of granulocytes was significantly higher than that of hyalinocytes for each pathogen. No difference in PI was observed in granulocytes and hyalinocytes. Two defense mechanisms of B. areolata were quantified using flow cytometry. Haemocyte phagocytosis was quantified using fluorescent microbeads and respiratory burst activity was measured using H2O2 increases detected by 2', 7'-dichlorofluorescein diacetate. Both phagocytosis and respiratory burst activity of the haemocytes increased over time. After 90 min the phagocytic rate no longer increased. In the case of respiratory burst, the greatest increase in fluorescence occurred between 30 and 120 min, no further increase was seen after 120 min. These results showed unequivocally that a native (unstimulated) haemocyte oxidative burst was active in B. areolata. The aim of this study was to further the knowledge of immunology in gastropods.

Kinetics and thermodynamics of glycans and glycoproteins binding to Holothuria scabra lectin: a fluorescence and surface plasmon resonance spectroscopic study

Holothuria scabra produces a monomeric lectin (HSL) of 182 kDa. HSL showed strong antibacterial activity and induced bacterial agglutination under in vitro conditions, indicating its role in animals' innate immune responses. Very few lectins have been reported from echinoderms and none of these lectins have been explored in detail for their sugar-binding kinetics. Affinity, kinetics and thermodynamic analysis of glycans and glycoproteins binding to HSL were studied by fluorescence and surface plasmon resonance spectroscopy. Lectin binds with higher affinity to O-linked than N-linked asialo glycans, and the affinities were relatively higher than that for sialated glycans and glycoproteins. T-antigen α-methyl glycoside was the most potent ligand having the highest affinity (Ka 8.32 ×10(7) M(-1)). Thermodynamic and kinetic analysis indicated that the binding of galactosyl Tn-antigen and asialo glycans is accompanied by an enthalpic contribution in addition to higher association rate coupled by low activation energy for the association process. Presence of sialic acid or protein matrix inhibits binding. Higher affinity of HSL for O-glycans than N-glycans had biological implications; since HSL specifically recognizes bacteria, which have mucin or O-glycan cognate on their cell surfaces and play a major role in animal innate immunity. Since, HSL had higher affinity to T-antigen, makes it a useful tool for cancer diagnostic purpose.

Effects of the dietary administration of sodium alginate on the immune responses and disease resistance of Taiwan abalone, Haliotis diversicolor supertexta

Sodium alginate extracted from brown algae was reported to enhance the immune response and resistance of fish and shrimp. In this study, survival rates of the abalone, Haliotis diversicolor supertexta, against Vibrio parahaemolyticus, and its non-specific immune parameters such as the total haemocyte count (THC), phenoloxidase (PO) activity, respiratory bursts, superoxide dismutase (SOD) activity, phagocytic activity, and clearance efficiency to V. parahaemolyticus by H. diversicolor supertexta were determined when abalone (4.5 ± 0.4 g) were fed diets containing sodium alginate at 0, 1.0, 2.0, and 3.0 g kg⁻¹. Abalone fed a diet containing sodium alginate at 2.0 and 3.0 g kg⁻¹ for 14 days and at 1.0 g kg⁻¹ for 21 days had significantly higher survival rates than those fed the control diet after challenge with V. parahaemolyticus. The relative survival percentages of abalone fed the 1.0, 2.0, and 3.0 g kg⁻¹ sodium alginate-containing diets for 14 and 21 days were 16.1%, 40.0%, and 48.0%, and 63.6%, 27.3% and 22.6%, respectively. The PO activity, respiratory bursts, SOD activity, and phagocytic activity and clearance efficiency of V. parahaemolyticus of abalone fed the sodium alginate-containing diets at 1.0, 2.0, and 3.0 g kg⁻¹ were significantly higher than those of abalone fed the control diet for 14 days. After 21 days, the PO activity, respiratory bursts, SOD activity, and phagocytic activity and clearance efficiency of V. parahaemolyticus by abalone fed the sodium alginate-containing diet at 1.0 g kg⁻¹ were significantly higher than those of abalone fed the other diets. It was concluded that sodium alginate can be used as an immunostimulant for abalone through dietary administration to enhance immune responses of abalone and resistance against V. parahaemolyticus, which were related to the dose and timing of administration.

Multicellular spheroid formation and evolutionary conserved behaviors of apple snail hemocytes in culture

A hemocyte primary culture system for Pomacea canaliculata in a medium mimicking hemolymphatic plasma composition was developed. Hemocytes adhered and spread onto culture dish in the first few hours after seeding but later began forming aggregates. Time-lapse video microscopy showed the dynamics of the early aggregation, with cells both entering and leaving the aggregates. During this period phagocytosis occurs and was quantified. Later (>4 h), hemocytes formed large spheroidal aggregates that increased in size and also merged with adjacent spheroids (24-96 h). Large single spheroids and spheroid aggregates detach from the bottom surface and float freely in the medium. Correlative confocal, transmission electron and phase contrast microscopy showed a peculiar organization of the spheroids, with a compact core, an intermediate zone with large extracellular lacunae and an outer zone of flattened cells; also, numerous round cells emitting cytoplasmic extensions were seen attaching to the spheroids' smooth surface. Dual DAPI/propidium iodide staining revealed the coexistence of viable and non-viable cells within aggregates, in varying proportions. DNA concentration increased during the first 24 h of culture and stabilized afterward. BrdU incorporation also indicated proliferation. Spontaneous spheroid formation in culture bears interesting parallels with spheroidal hemocyte aggregates found in vivo in P. canaliculata, and also with spheroids formed by tumoral or non-tumoral mammalian cells in vitro.

Pathological and physiological effects of nicking on brown crab (Cancer pagurus) in the Irish crustacean fishery

Nicking is used in fisheries to immobilize claws of brown crab (Cancer pagurus) in order to prevent cannibalism and fighting during storage. Nicking fractures the apodemes creating an open wound and damage to the internal claw tissues, which is the most valuable product of brown crab. In turn, this results in a reduction of quality of product and possibly compromises the host's defence mechanisms to other physiological challenges experienced throughout the post-harvest process. This study assessed the effects of nicking on the physiology and pathology of brown crab from the Irish fishery over 7 days. Results showed significantly elevated levels of muscle necrosis (P=0.005), total pathologies (P=0.022) and encirculating granulocytes in nicked crab compared to non-nicked crab. Mean glucose (212.0 μg/mL±108.4), lactate (36.52 μg/mL±38.74) and RI (11.05n±1.78) levels were higher in nicked crab indicating increased stress levels. Overall, histology results showed a significantly higher (P=0.022) occurrence of pathologies, such as melanised nodules, in nicked animals. In addition to an observed reduction in the quality of claw muscle, nicked crab also showed significantly higher (P=0.005) levels of necrosis in claw muscle. From the results of this study it is recommended that alternative retention methods are used.

Modulation of the innate immune system in white shrimp Litopenaeus vannamei following long-term low salinity exposure

Immune parameters, haemocyte lifespan, and gene expressions of lipopolysaccharide and β-glucan-binding protein (LGBP), peroxinectin (PX), integrin β, and α2-macroglobulin (α2-M) were examined in white shrimp Litopenaeus vannamei juveniles (0.48 ± 0.05 g) which had been reared at different salinity levels of 2.5‰, 5‰, 15‰, 25‰, and 35‰ for 24 weeks. All shrimp survived during the first 6 weeks. The survival rate of shrimp reared at 2.5‰ and 5‰ was much lower (30%) than that of shrimp reared at 15‰, 25‰, and 35‰ (76%~86%) after 24 weeks. Shrimp reared at 25% grew faster. Shrimp reared at 2.5‰ and 5‰ showed lower hyaline cells (HCs), granular cells (GCs), phenoloxidase activity (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, and lysozyme activity, but showed a longer haemocyte lifespan, and higher expressions of LGBP, PX, integrin β, and α2-M. In another experiment, shrimp which had been reared at different salinity levels for 24 weeks were challenged with Vibrio alginolyticus (6 × 10(6) cfu shrimp(-1)), and WSSV (10(3) copies shrimp(-1)) and then released to their respective seawater. At 96-144 h, cumulative mortalities of shrimp reared at 2.5‰ and 5‰ were significantly higher than those of shrimp reared at 15‰, 25‰, and 35‰. It was concluded that following long-term exposure to 2.5‰ and 5‰ seawater, white shrimp juveniles exhibited decreased resistance against a pathogen due to reductions in immune parameters. Increases in the haemocyte lifespan and gene expressions of LGBP, integrin β, PX, and α2-M indicated that shrimp had the ability to expend extra energy to modulate the innate immune system to prevent further perturbations at low salinity levels.

Identification and characterisation of the Mpeg1 homologue in the South African abalone, Haliotis midae

Although Haliotis midae is the most economically important cultured abalone species in South Africa, infectious diseases have the potential to severely limit the production of this shellfish. Consequently, it is becoming increasingly important to characterise the abalone immune system in order to better understand their ability to combat infection. This study reports the identification and characterisation of a perforin-like protein, designated hmMpeg1, which is believed to be involved in the H. midae immune system. hmMpeg1 encodes for a 78 kDa protein that has significant sequence similarity to Mpeg proteins from other abalone species and includes the conserved cytolytic membrane attack complex/perforin (MACPF) domain of perforin. Real-time quantitative PCR (qPCR) analysis demonstrated expression of hmMpeg1 mRNA in haemocytes and epipodia samples from H. midae exposed to a heat-killed, Gram-negative bacterial pathogen, Vibrio anguillarum 5676. hmMpeg1 mRNA in haemocytes increased significantly 48 h post-infection (h.p.i) (8.2 fold; P < 0.05), coinciding with a decrease in the total number of circulating haemocytes, and reached a maximum at 96 h.p.i (17.2 fold; P < 0.05). Similarly, a significant increase in the level of hmMpeg1 mRNA occurred at 24 h.p.i in epipodia samples (3.8 fold; P < 0.05), reaching a maximum at 48 h.p.i (4.5 fold; P < 0.05). In addition, western blot analysis detected a significant increase in hmMpeg1 between 24 h.p.i (4.2 fold; P < 0.05) and 48 h.p.i (3.1 fold; P < 0.05) in the epipodia, and between 48 h.p.i (1.7 fold; P < 0.05) and 96 h.p.i (1.9 fold; P < 0.05) in haemocytes, sampled from abalone exposed to the abalone pathogen V. anguillarum 5676. The importance of hmMpeg1, in terms of its function and importance in the H. midae immune response, is discussed.

Immune responses to combined effect of hypoxia and high temperature in the green-lipped mussel Perna viridis

Flow cytometry was used to examine immune responses in haemocytes of the green-lipped mussel Perna viridis under six combinations of oxygen level (1.5 mg O2 l(-1), 6.0 mg O2 l(-1)) and temperature (20 °C, 25 °C and 30 °C) at 24 h, 48 h, 96 h and 168 h. The mussels were then transferred to normoxic condition (6.0 mg O2 l(-1)) at 20 °C for further 24 h to study their recovery from the combined hypoxic and temperature stress. Esterase (Est), reactive oxygen species (ROS), lysosome content (Lyso) and phagocytosis (Pha) were reduced at high temperatures, whereas hypoxia resulted in higher haemocyte mortality (HM) and reduced phagocytosis. For HM and Pha, changes were observed after being exposed to the stresses for 96 h, whereas only a 24 h period was required for ROS and Lyso, and a 48 h one for Est. Recovery from the stresses was observed for HM and Pha but not other immune responses.

Modulation and Interaction of Immune-Associated Parameters with Antioxidant in the Immunocytes of Crab Scylla paramamosain Challenged with Lipopolysaccharides

Invertebrates are dependent on cellular and humoral immune defences against microbial infection. Scylla paramamosain is an important commercial species, but the fundamental knowledge on its immune defense related to the antioxidant and immune-associated reactions is still lacking. The study was to differentiate the responses of immune-associated parameters of haemolymph components in S. paramamosain when challenged with bacterial lipopolysaccharides (LPSs). The immunostimulating effects of LPS in crab by triggering various immune parameters (phagocytosis, lysozyme, antibacterial activity, phenoloxidase, and the generation of superoxide and nitric oxide) were investigated. Results showed that the generation of free radicals, phenoloxidase, lysozyme and antibacterial activities was significantly increased through the exposure periods. Conversely, total hemocyte count and lysosomal membrane stability decreased significantly as the exposure period extended to 96 h. The relationship between the antioxidant enzymes and immune reactions due to LPS was highly significant. In addition, ROS production was positively correlated with antioxidant showing immediate response of antioxidant defense to the oxyradicals generated. Overall, the study indicated that nonspecific immune components in hemocytes of crab showed active response to the LPS stimulation, and their responses suggested that many immune-associated parameters could be modulated and interrelated with the influence of antioxidants in crustaceans.