Signal transduction of the prophenoloxidase activating system of prawn haemocytes triggered by CpG oligodeoxynucleotides

Effectiveness of dietary heat-killed Bacillus subtilis harboring plasmid containing 60 copies of CpG-ODN 1668 against Vibrio harveyi in Penaeus vannamei

The cost of the purification process hinders the extensive use of cytosine phosphate guanosine-oligodeoxynucleotides (CpG-ODNs) for shrimp culture. Therefore, this study used a shuttle vector plasmid to carry 60 copies of CpG-ODN 1668 (pAD43-25_60CpG), which can replicate in Escherichia coli and Bacillus subtilis strain RIK1285. The first experiment used a reverse gavage procedure to deliver a substance (PBS [CK], pAD43-25 [P0], and pAD43-25_60CpG [P60], respectively) directly into the anterior midgut of Penaeus vannamei and transcriptome sequence analysis with a reference genome was performed to examine the expression of well-known immune-related genes. The results showed that the expression levels of immune-related genes in P60 group were significantly increased, particularly those associated with AMPs. In addition, using RT‒qPCR, the expression levels of AMP genes (LvALF, LvPEN-2, and LvPEN-3) in the P60 group may vary depending on the tissue and time point. The second experiment used dietary supplementation with three kinds of heat-killed B. subtilis (HKBS, HKBS-P0, and HKBS-P60) in 28 days of feeding experiments. The results showed that dietary supplementation with HKBS-P60 did not significantly improve shrimp growth performance and survival. However, on days 14 and 28 of the feeding regimens, alkaline phosphatase (AKP) and acid phosphatase (ACP) activity were considerably higher than in other treatments. In addition, following infection with Vibrio harveyi, AKP and ACP activity in the HKBS-P60 group was significantly higher than in other treatments, particularly at the early stage of bacterial infection. Moreover, HKBS-P60 was found to be better protected against V. harveyi infection with lower cumulative mortality (60%) compared to HKBS (90%) and HKBS-P0 (100%) at 7 days after infection. Overall, these findings confirmed that P60 could increase immunological responses in the shrimp midgut, and HKBS-P60 could be used as an effective tool to enhance the immune response and disease resistance in shrimp.

ERK is involved in the regulation of CpG ODN 2395 on the expression levels of anti-lipopolysaccharide factors in Chinese mitten crab, Eriocheir sinensis

CpG oligodeoxynucleotides (ODN), as an effective adjuvant or immunopotentiator, activate the immune system and induce various immune responses. Recently, it has also been reported that high dose of CpG ODN can lead to immunosuppression. However, the underlying mechanism of CpG ODN-mediated immune response remains largely unknown in invertebrates. In the present study, the role of ERK in regulating expression levels of anti-lipopolysaccharide factors (ALFs) induced by different doses of CpG ODN 2395 was analyzed in Chinese mitten crab, Eriocheir sinensis. The mRNA expression levels of EsALFs (EsALF1, EsALF2 and EsALF3) and EsERK in haemocytes were observed to increase from 6 h to 48 h post low doses of CpG ODN 2395 (0.5 μg and 2.5 μg) stimulation, while they were suppressed after high dose of CpG ODN 2395 (12.5 μg) injection. Meanwhile, the phosphorylation levels of ERK in haemocytes were significantly promoted after low doses of CpG ODN 2395 injection, and a reduce level of ERK phosphorylation was observed after high dose of CpG ODN 2395 injection. Further investigation showed that the expression levels of EsALFs induced by CpG ODN 2395 were markedly down-regulated after knocking down the expression of EsERK. Similarly, the EsALFs mRNA expression were also inhibited post different doses of CpG ODN 2395 stimulation in PD98059 (ERK inhibitor) injection crabs. These results collectively suggest that ERK is involved in regulating the expression level of EsALFs induced by different dose of CpG ODN 2395 in Chinese mitten crab, which contribute to the understanding of the regulation of CpG ODN involving in immune response in crustaceans.

Caspase-3, a shrimp phosphorylated hemocytic protein is necessary to control YHV infection

By using immunohistochemistry detection, yellow head virus (YHV) was found to replicate in granule-containing hemocytes including semi-granular hemocytes (SGC) and granular hemocytes (GC) during the early phase (24 h post injection) of YHV-infected shrimp. Higher signal of YHV infection was found in GC more than in SGC. Comparative phosphoproteomic profiles between YHV-infected and non-infected GC reveal a number of phosphoproteins with different expression levels. The phosphoprotein spot with later on identified as caspase-3 in YHV-infected GC is most interesting. Blocking caspase-3 function using a specific inhibitor (Ac-DEVD-CMK) demonstrated high replication of YHV and consequently, high shrimp mortality. The immunohistochemistry results confirmed the high viral load in shrimp that caspase-3 activity was blocked. Caspase-3 is regulated through a variety of posttranslational modifications, including phosphorylation. Analysis of phosphorylation sites of shrimp caspase-3 revealed phosphorylation sites at serine residue. Taken together, caspase-3 is a hemocytic protein isolated from shrimp granular hemocytes with a role in anti-YHV response and regulated through the phosphorylation process.

Dietary supplementation of marine yeast Yarrowia lipolytica modulates immune response in Litopenaeus vannamei

The immunostimulatory potential of the marine yeast Yarrowia lipolytica (D1 and N6 strains) administered orally was evaluated in the white shrimp Litopenaeus vannamei. Yeasts and commercial glucans were mixed with a commercial feed to formulate diets with a 1.1% concentration of immunostimulants. The shrimp were fed daily for a period of 21 days. Weekly determinations were performed for immunological parameters in hemolymph, such as total hemocyte count (THC), lysozyme activity (LYZ), prophenoloxidase activity, antioxidant enzymatic activities (superoxide dismutase [SOD], catalase [CAT], and peroxidases), and bactericidal activity against Vibrio parahaemolyticus. Expression profiles of penaeidin (PEN), lysozyme (LYZ), and prophenoloxidase (proPO) immune genes were evaluated in hemocytes. In general, an increase in the immune parameters was observed in shrimp fed yeast diet compared to glucan and the control diets. Yarrowia lipolytica, especially strain N6, provided maximum immunostimulatory effects evidenced by the increase of immune parameters (THC, LYZ, SOD, CAT) and gene expression profile. In conclusion, this study demonstrated that Y. lipolytica had immunostimulatory effects and increased bactericidal activity in L. vannamei hemocytes against V. parahaemolyticus. These findings open the path for the potential application of Y. lipolytica-based immunostimulant for shrimp aquaculture.

Crustacean hyperglycemic hormone (CHH) affects hemocyte intracellular signaling pathways to regulate exocytosis and immune response in white shrimp Litopenaeus vannamei

Recombinant Litopenaeus vannamei CHH (rLvCHH) was obtained from a bacterial expression system and the intracellular signaling pathways involved in exocytosis and immune response after rLvCHH injection (0.2 and 2 μg/shrimp) was investigated in this study. The results showed that CHH contents increased 51.4%-110.2% (0.2 μg/shrimp) and 65.0%-211.3% (2 μg/shrimp) of the control level. And the contents of three biogenic amines in hemolymph presented a similar variation pattern after rLvCHH injection, but reached the highest level at different time points. Furthermore, the mRNA expression levels of membrane-bound guanylyl cyclase (mGC) (1.20-1.93 fold) and biogenic amine receptors, including type 2 dopamine receptor (DA2R) (0.72-0.89 fold), α2 adrenergic receptor (α2-AR) (0.72-0.91 fold) and 5-HT7 receptor (5-HT7R) (1.37-3.49 fold) in hemocytes were changed consistently with their ligands. In addition, the second messenger and protein kinases shared a similar trend and reached the maximum at the same time respectively. The expression levels of nuclear transcription factor (cAMP response element-binding protein, CREB) and exocytosis-related proteins transcripts were basically overexpressed after rLvCHH stimulation, which reached the peaks at 1 h or 3 h. Eventually, the phenoloxidase (PO) activity (37.4%-158.5%) and antibacterial activity (31.8%-122.3%) in hemolymph were dramatically enhanced within 6 h, while the proPO activity in hemocytes significantly decreased (11.2%-62.6%). Collectively, these results indicate that shrimps L. vannamei could carry out a simple but 'smart' NEI regulation by releasing different neuroendocrine factors at different stages after rLvCHH stimulation, which could couple with their receptors and trigger the downstream signaling pathways during the immune responses in hemocytes.

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.

Effects of ammonia-N exposure on the concentrations of neurotransmitters, hemocyte intracellular signaling pathways and immune responses in white shrimp Litopenaeus vannamei

The effects of ammonia-N exposure (transferred from 0.07 to 2, 10 and 20 mg L^-1) on the mechanism of neuroendocrine-immunoregulatory network were investigated in Litopenaeus vannamei. The results showed that biogenic amines (dopamine, noradrenaline, 5-hydroxytryptamine) concentrations in treatment groups increased significantly within 12 h. The gene expression of guanylyl cyclase increased significantly from 3 h to 24 h. And dopamine receptor D₄ and α₂ adrenergic receptor gene expression in treatment groups decreased significantly within 12 h, whereas the mRNA expression of 5-HT₇ receptor increased significantly within 3 h and reached the peak levels at 6 h. The second messengers (cAMP, cGMP) and Calmodulin (CaM) increased significantly in treatment groups after 3 h. The concentrations of protein kinases (PKA, PKG) shared a similar trend in cAMP and cGMP which were up-regulated and reached the peak value at 6 h, while the PKC decreased within 3 h and arrived at its bottom at 6 h. The nuclear factor kappa-b and cAMP-response element binding protein mRNA expression levels of treatment shrimps increased sharply and reached maximum values at 6 h. The total hemocyte count, phagocytic activity, antibacterial activity in treatment groups decreased dramatically within 48 h. Whereas the phenoloxidase activities slightly up-regulated. Then it was decreased significantly up to 48 h. α₂-macroglobulin activity decreased at the first 3 h-stress. Then they up-regulated significantly in 6 h. The results suggest that there are two crucial neuroendocrine substances (biogenic amine and CHH), which play a principal role in adapting to ammonia-N exposure and cause immune response through cAMP-, CaM- and cGMP-dependent pathways.

Impacts of environmental and biological stressors on immune system of Macrobrachium rosenbergii

Macrobrachium rosenbergii commonly called giant freshwater prawn is a widely farmed crustacean in freshwater. Similar to other aquatic organisms, their growth and well‐being is influenced by various physical, chemical and biological factors. We discuss about the critical growth limiting factors as well as disease causing agents and the potential immune molecules of M. rosenbergii that are proved to involve in preventing and/or responding to those limiting factors.

Activation mechanism of a neuromodulator-gated pacemaker ionic current

The neuromodulator-gated current (I_MI) found in the crab stomatogastric ganglion is activated by neuromodulators that are essential to induce the rhythmic activity of the pyloric network in this system. One of these neuromodulators is also known to control the correlated expression of voltage-gated ionic currents in pyloric neurons, as well as synaptic plasticity and strength. Thus understanding the mechanism by which neuromodulator receptors activate I_MI should provide insights not only into how oscillations are initiated but also into how other processes, and currents not directly activated by them, are regulated. To determine what specific signaling molecules are implicated in this process, we used a battery of agonists and antagonists of common signal transduction pathways. We found that the G protein inhibitor GDPβS and the G protein activator GTPγS significantly affect I_MI amplitude, suggesting that its activation is mediated by G proteins. Interestingly, when using the more specific G protein blocker pertussis toxin, we observed the expected inhibition of I_MI amplitude but, unexpectedly, in a calcium-dependent fashion. We also found that antagonists of calcium- and calmodulin-associated signaling significantly reduce I_MI amplitude. In contrast, we found little evidence for the role of cyclic nucleotide signaling, phospholipase C (PLC), or kinases and phosphatases, except two calmodulin-dependent kinases. In sum, these results suggest that proctolin-induced I_MI is mediated by a G protein whose pertussis toxin sensitivity is altered by external calcium concentration and appears to depend on intracellular calcium, calmodulin, and calmodulin-activated kinases. In contrast, we found no support for I_MI being mediated by PLC signaling or cyclic nucleotides.NEW & NOTEWORTHY Neuronal rhythmic activity is generated by either network-based or cell-autonomous mechanisms. In the pyloric network of decapod crustaceans, the activation of a neuromodulator-gated pacemaker current is crucial for the generation of rhythmic activity. This current is activated by several neuromodulators, including peptides and acetylcholine, presumably via metabotropic receptors. We have previously demonstrated a novel extracellular calcium-sensitive voltage-dependence mechanism of this current. We presently report that the activation mechanism depends on intracellular and extracellular calcium-sensitive components.

Further evidences for the mode of action of the larvicidal m-pentadecadienyl-phenol isolated from Myracrodruon urundeuva seeds against Aedes aegypti

Nowadays, dengue fever is considered the most important arbovirosis worldwide and its control is still based upon combating the vector Aedes aegypti. Besides monitoring of mosquito populations resistant to conventional insecticides, the search for new environmentally safe insecticides and conduction of molecular studies focusing on the elucidation of mode of action and possible resistance mechanisms are considered the key for a sustainable management of the mosquito vector. Thus, the present work aimed to assess changes in protein expression of 3rd-instar larvae of Ae. aegypti after exposure to the natural insecticide m-pentadecadienyl-phenol. Bidimensional electrophoresis followed by mass spectrometry resulted in identification of 12 proteins differentially expressed between control and treated groups. Larvae exposed to the toxic compound for 24h showed elevated detoxification response (glutathione-S-transferase), increased levels of stress-related proteins (HSP70) as well as evidence of lysosome stabilization to enable survival. Furthermore, expression of proteins involved in protection of peritrophic membrane and metabolism of lipids indicated systemic effect of toxic effects in treated larvae.

Immune responses of prophenoloxidase in the mud crab Scylla paramamosain against Vibrio alginolyticus infection: in vivo and in vitro gene silencing evidence

Phenoloxidase (PO) plays an important role in arthropod melanization. In the present study, a proPO gene was obtained from the mud crab Scylla paramamosain, then we localized the proPO mRNA in hemocytes and detected the expression of proPO after bacterial challenge. In vivo and in vitro gene silencing mediated by dsRNA was also used to investigate the function of proPO in innate immune. The full-length of the proPO cDNA was 2600 bp and the predicted ORF encoded a protein of 673 amino acids with a predicted molecular mass of 77.3 kDa. The deduced amino acid and the main functional domain of proPO shared a high similarity to the mud crab Scylla serrata. In situ hybridization assay showed that the proPO mRNA was localized in the granular and semi-granular cells. The expression level of proPO in hemocytes showed a clear time-dependent pattern during the 96 h course after stimulated by Vibrio alginolyticus. In this study, high expression levels were observed at 3, 12, 24 and 48 h, respectively and the highest expression level was observed at 12 h, and this suggested that proPO was induced by bacteria and involved in immune response. In vivo proPO and GFP dsRNA treatment experiments showed that, proPO mRNA transcript was reduced to 39%, but the PO activity showed no significant difference (P > 0.05). Results indicated that the expression of proPO could be inhibited by dsRNA, and the enzyme activity may be influenced by incomplete knockdown of proPO, or hemocyanin, and other proPO isoforms as well. In vitro proPO-silenced experiments showed that the levels of proPO were decreased by 36%, 64% and 77% at 8, 16 and 32 h, respectively. Meanwhile, the quantity of bacteria was significantly larger in proPO dsRNA treatment than that in control at 3 h, calculated by 4,6-diamino-2-phenylindole staining (P < 0.01). These data demonstrated that the proPO gene plays an important role in the control of systemic bacterial infections and could help us to elucidate the defense role of the proPO-activating system in crabs. In addition, in vitro gene silencing operation mediated by dsRNA was expected to be a new tool for investigating the function of genes in crustaceans in the case of lacking cell line.

The immune responses triggered by CpG ODNs in shrimp Litopenaeus vannamei are associated with LvTolls

CpG oligodeoxynucleotides (ODNs) represent a kind of pathogen-associated molecular patterns (PAMPs) as well as a novel adjuvant that activate the innate immune system through interaction with Toll-like receptor 9 (TLR9) in mammals. In the present study, the synthetic oligodeoxynucleotides, CpG ODN 2395, was employed to investigate the interactive mode of CpG ODNs with three known Tolls (LvToll1-3) from shrimp Litopenaeus vannamei. The mature peptides of extracellular domains of LvTolls (LvToll-ECDs) were recombinant expressed and their binding activities to CpG ODN 2395 were further examined by ELISA. rLvToll1-ECD and rLvToll3-ECD exhibited affinity to CpG ODN 2395 in a dose-dependent manner when their concentrations ranged from 0.25 to 2.00 μmol/L, while rLvToll2-ECD did not show any binding activities to CpG ODN 2395 in tested concentrations. Additionally, after the stimulation of CpG ODN 2395, the luciferase activities of HEK293T cells transfected with LvToll1-mosaic or LvToll3-mosaic were significantly increased to 2.38-fold (p<0.01) and 1.56-fold (p<0.01), while that in the HEK293T cells transfected with LvToll2-mosaic declined to 0.41-fold. The TNF-α activities were significantly enhanced (p<0.01), and a significant increase (p<0.05) of the NO production was observed at 12h post CpG ODN 2395 stimulation. Moreover, the induced TNF-α activities and increased NO production triggered by CpG ODN 2395 were abolished after the treatment of chloroquine (CQ). The uptake of CpG ODN 2395 by shrimp haemocytes was investigated using the laser scanning confocal microscope, and CpG ODN 2395 was observed to be internalized by the haemocytes and distributed in the cytoplasm with aggregated signals around the nucleuses. It suggested that the interactions of CpG ODNs with LvToll1 and LvToll3 as well as the mature of endosomes in the haemocytes of shrimp L. vannamei were indispensable for the triggering of immune responses by CpG ODNs, and the results provided a foundation for the application of CpG ODNs as the novel immunostimulants in aquaculture.

The CpG ODNs enriched diets enhance the immuno-protection efficiency and growth rate of Chinese mitten crab, Eriocheir sinensis

CpG oligodeoxynucleotides (ODNs), the well-known vaccine adjuvant in mammals, have been proved to mount innate immune responses in crustaceans. In the present study, CpG ODNs was employed as supplements in diets to fed crab Eriocheir sinensis, and the changes of immune parameters as well as weight gain were investigated to evaluate its possible application in crab farming. After the crabs were fed with 40 mg/kg and 100 mg/kg CpG ODNs containing diets (designated as C40 and C100 group) for four weeks, the lysozyme activities were significantly enhanced (p < 0.01) in both groups, while the catalase activity was only increased (p < 0.01) in the C40 group. When those crabs were subsequently challenged with Aeromonas hydrophila, the cumulative mortalities in C40 and C100 groups were declined by 10.4% and 10.8% (p < 0.05) compared with that of control group, respectively. Interestingly, the final weights of crabs were increased after four weeks' feeding of CpG ODNs, and the percentage of weight gain in C40 group reached 124.5 ± 14.2%, which was significantly higher (p < 0.05) than that of control group (78.1 ± 19.2%) and C100 group (107.3 ± 28.2%). The uptake of CpG ODNs by haemocytes and the possible mechanism of CpG ODNs to active the immune response were investigated by using the laser scanning confocal microscope. CpG ODNs (labeled with 5'-end-FAM) could be internalized by the haemocytes after incubation of 20 min, with strong signals detected at the cell membrane and in the cytoplasm. In the cytoplasm, most of the CpG ODNs were localized in lysosome, and some of them escaped from the lysosomal compartments and aggregated around the nuclear. The results clearly demonstrated that CpG ODNs could be internalized directly by crab haemocytes and mostly located in the late endosome. The enhancements of immuno-protection efficiency and growth rate from CpG ODNs as supplements in diets might depend on the uptaking and locating processes, and they could be used as a potential immunostimulant for the crab aquaculture.

Hemocytic immune responses triggered by CpG ODNs in shrimp Litopenaeus vannamei

CpG oligodeoxynucleotides (CpG ODNs), also called bacterial DNA or synthetic oligodeoxynucleotides, can induce apparent immunity protection against various pathogens, and they are widely used as functional immunostimulant or vaccine adjuvant in mammals. In the present study, CpG-rich plasmid pUC57-CpG was constructed and employed to stimulate the shrimp Litopenaeus vannamei, and the total hemocyte count, percentage of apoptotic hemocytes, regeneration of circulating hemocytes, the ability of phagocytosis and generation of reactive oxygen species (ROS) were measured to reveal the possible protection mechanism of CpG ODNs. After the injection of pUC57-CpG, the total hemocyte count significantly decreased (p < 0.01) to 2.56 × 10(7) cell/mL at the first day post stimulation, while the apoptosis increased (p < 0.01), which was 1.72-fold of that in control group. At the same time, the regeneration of circulating hemocytes fluctuated in a similar trend, and a significant increase was observed at the first day post stimulation. The phagocytotic activity including the percentage of phagocytosis and phagocytotic index, experienced an upward tend during the whole experimental period and the ROS level increased by 22% (p < 0.05) compared to that in the control group at first day post stimulation. These results together suggested that pUC57-CpG could promote the apoptosis and regeneration of circulating hemocytes, and enhance the phagocytosis and ROS production, which might contribute to the boosted immunity against the infection of pathogens.

A clip domain serine protease (cSP) from the Chinese mitten crab Eriocheir sinensis: cDNA characterization and mRNA expression

Clip domain serine protease (cSP), characterized by conserved clip domains, is a new serine protease family identified mainly in arthropod, and plays important roles in development and immunity. In the present study, the full-length cDNA of a cSP (designated EscSP) was cloned from Chinese mitten crab Eriocheir sinensis by expressed sequence tags (ESTs) and PCR techniques. The 1380 bp EscSP cDNA contained a 1152 bp open reading frame (ORF) encoding a putative cSP of 383 amino acids, a 5'-untranslated region (UTR) of 54 bp, and a 3'-UTR of 174 bp. Multiple sequence alignment presented twelve conserved cysteine residues and a canonical catalytic triad (His(185), Asp(235) and Ser(332)) critical for the fundamental structure and function of EscSP. Two types of cSP domains, the clip domain and tryp_spc domain, were identified in the deduced amino acids sequence of EscSP. The conservation characteristics and similarities with previously known cSPs indicated that EscSP was a member of the large cSP family. The mRNA expression of EscSP in different tissues and the temporal expression in haemocytes challenged by Listonella anguillarum were measured by real-time RT-PCR. EscSP mRNA transcripts could be detected in all examined tissues, and were higher expressed in muscle than that in hepatopancreas, gill, gonad, haemocytes and heart. The EscSP mRNA expression in haemocytes was up-regulated after L. anguillarum challenge and peaked at 2 h (4.96 fold, P < 0.05) and 12 h (9.90 fold, P < 0.05). Its expression pattern was similar to prophenoloxidase (EsproPO), one of the components of crab proPO system found in our previous report. These results implied that EscSP was involved in the processes of host-pathogen interaction probably as one of the proPO system members.

Inhibitor of REL/NF-KappaB is regulated in Sydney rock oysters in response to specific double-stranded RNA and Vibrio alginolyticus, but the major immune anti-oxidants EcSOD and Prx6 are non-inducible

Invertebrates, such as oysters have mechanisms to recognize different microbial associated molecular patterns (MAMPs) and recognition of these antigens triggers signaling pathways for the transcription of immune-related proteins. Components of the Rel/NF-(capital KA, Cyrillic)B pathway have been identified in mollusks but the role of different MAMPs in the activation of this pathway is poorly understood. In the current study, the Sydney rock oyster (Saccostrea glomerata) was injected intramuscularly with a range of different MAMPs. Oysters were sampled over a 24 h period and the difference in expression of genes associated with immunity was determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR) using RNA extracted from hemocytes. The results showed that oysters can discriminate between different nucleic acids and double-stranded RNA sequences for activation of the Rel/NF-(capital KA, Cyrillic)B pathway in S. glomerata. Polyinosinic-polycytidylic acid (poly I:C) up-regulated expression of inhibitor of Rel/NF-(capital KA, Cyrillic)B (I(capital KA, Cyrillic)B) by 26-fold and interferon-inhibiting cytokine (IK) by 2.2-fold, whereas polycytidylic acid-polyguanylic acid (poly G:C) and double stranded Vibrio alginolyticus genomic DNA (dsDNA) did not. I(capital KA, Cyrillic)B was also up-regulated 3.8-fold higher for oysters stimulated with V. alginolyticus bacterial cells suggesting that lipopolysaccharide (LPS) also activates the Rel/NF-(capital KA, Cyrillic)B pathway. The expressions of extracellular superoxide dismutase (EcSOD) and peroxiredoxin 6 (Prx6) were not significantly affected by dsRNA, dsDNA or V. alginolyticus bacterial cells suggesting that these two genes, previously demonstrated to be important in the resistance of S. glomerata to disease are not directly inducible by these MAMPs. This is the first study investigating differences in expression kinetics of immune genes in response to challenge from different MAMPs in this economically important bivalve species.

Innate hemocyte responses of Malacosoma disstria larvae (C. Insecta) to antigens are modulated by intracellular cyclic AMP

Invertebrate intracellular hemocyte signaling pathways affecting cellular-antigen responses, although defined for molluscs and some arthropods including dipteran insects, is less known for lepidopterans. Hemocytic-antigen responses of the arboreal pest lepidopteran Malacosoma disstria are linked to cAMP-dependent protein kinase A implicating cAMP in cellular hemocyte immune responses. The purpose in the present study was to determine intracellular cAMP effects on larval M. disstria hemocytes adhering to slides and bacteria. Altering adenylate cyclase and phosphodiesterase activities as well as cAMP levels in vitro and in vivo changed hemocyte responses to antigens. Quiescent hemocytes had high cAMP levels due to adenylate cyclase activity and possibly low phosphodiesterase (type 4) activity. Antigen contact diminished hemocytic cAMP levels. Inhibiting adenylate cyclase increased hemocyte-antigen and hemocyte-hemocyte adhesion, the latter producing nodules in vivo without bacterial antigens. Inhibiting phosphodiesterase type 4 produced the reverse effects. Pharmacologically increasing intracellular cAMP in attached hemocytes caused many of the cells to detach. Diminished intracellular cAMP changed hemograms in vivo in bacteria-free larvae comparable to changes induced by the bacterium, Bacillus subtilis, by producing nodules. Lowering cAMP enhanced also the removal of Xenorhabdus nematophila and B. subtilisin vivo.

The effect of two CpG oligodeoxynucleotides with different sequences on haemocytic immune responses of giant freshwater prawn, Macrobrachium rosenbergii

A previous study has demonstrated that the intrahaemocytic phenoloxidase (PO) activity of the prawn Macrobrachium rosenbergii was enhanced by CpG oligodeoxynucleotide (ODN) 2006, but not by os-ODN13. The study described herein determined the binding characteristics of the two ODNs to haemocytes. Treating haemocytes with FAM-ODN or FAM-ODN plus different concentrations of the same ODN revealed that both ODNs specifically bound to haemocytes. Results from haemocytes treated with FAM-ODN2006 plus ROX-os-ODN13 in a competitive assay indicated that about 91% of haemocytes were simultaneously bound by the two ODNs and that the remaining haemocytes were only bound by ODN2006; moreover, ODN2006 binding to haemocytes was stronger than that of os-ODN13. To clarify the interactive effect of the two ODNs on haemocytic function, mRNA levels of haemocytic genes from single or double ODN-injected prawns were determined by semi-quantitative RT-PCR. The expression of either the prophenoloxidase (proPO) or peroxinectin (pon) genes was elevated by ODN2006 but reduced by os-ODN13; furthermore, ODN2006-increased proPO expression was abated following treatment with os-ODN13. In comparison with ODN-injected prawns alone, the NF-kappaB inhibitor PDTC reduced the proPO mRNA levels induced by ODN2006, but it elevated proPO expression inhibited by os-ODN13. These results support the notion that os-ODN13 may be able to neutralise or negate the enhancing effect of ODN2006 on proPO expression via the NF-kappaB signalling pathway as well as an unknown signalling pathway.

Construction of a recombinant plasmid containing multi-copy CpG motifs and its effects on the innate immune responses of aquatic animals

Bacterial DNA and synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG dinucleotides (CpG motifs) have been shown to induce potential immune responses. In this study, we designed a recombinant plasmid containing multi-copy CpG motifs, and observed its effects on innate immune responses of fish and prawn. The results showed that such plasmid DNA, compared to the vacant vector, can highly induce the activation of head kidney macrophages and the proliferation of peripheral blood leukocytes in Carassius auratus and Lateolabrax japonicus in vitro, as well as the activity of humoral defense proteins and the antibacterial activity of haemolymph in Litopenaeus vannamei in vivo. It implies that the multi-copy CpG motifs harboured in plasmid could contribute to these innate immunostimulatory effects. Therefore, the study suggested that the plasmid containing multi-copy CpG motifs might have its potential application in improving host resistance to pathogen insults in aquaculture, and have its notable advantages of high efficacy, economical cost and application to a broad range of aquatic species.

Cloning the prophenoloxidase cDNA and monitoring the expression of proPO mRNA in prawns (Macrobrachium rosenbergii) stimulated in vivo by CpG oligodeoxynucleotides

The prophenoloxidase (proPO) system forms the basis of the non-specific defence system in crustaceans. The aim of this study was to develop an RT-PCR procedure to determine proPO gene expression. We used several degenerate primers designed from the conserved regions in amino acid sequences of proPOs from other species to clone the possible cDNA(s) from the haemocytes of the prawn Macrobrachium rosenbergii. One DNA fragment, 2016 bp long, was cloned by a combination of reverse transcriptase-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (3'/5'-RACE). This fragment could encode a putative polypeptide with 671 amino acids. Further analysis showed that this putative polypeptide contained six histidine residues and a thiol ester-like motif (GCGWPRHM) just like the structural features of proPOs from the shrimp Penaeus monodon. A partial fragment of the sequence with 934 bp containing three histidine residues and the thiol ester-like motif was used as a target to monitor the activation of the proPO gene by the semi-quantitative RT-PCR analysis. The result showed that the highest level of proPO mRNA was detected at 1h after in vivo injection with 5 microg of CpG oligodeoxynucleotide 2006 per prawn; in the same experiment, the highest PO activity was detected at 6 h after injection. In the control, a continuous and slow elevation of PO activity was observed during the experimental period, but such elevation of proPO mRNA was not observed. From our previous study and the time course of gene expression of proPO and enzymatic activity of PO in this study, it can be concluded that the enhancement effect was through its transcriptional level, its translational level and then its post-translational level sequentially. These results suggest that, both for reliability, sensitivity and for the timing of sampling, the change in proPO mRNA is more useful than the PO activity in monitoring the activation of the proPO non-specific defence system of prawns after treatment with stimulants.