The immune response of white shrimp Litopenaeus vannamei following Vibrio alginolyticus injection

Dietary fulvic acid improves immune, digestive and antioxidant parameters in juvenile white-leg shrimp (Litopenaeus vannamei) in a super-intensive system

In the current study, the effects of dietary fulvic acid supplementation at levels of 0.5, 1 and 2% were examined in white-leg shrimp, Litopenaeus vannamei. A significant increase in the weight of the shrimp was observed in the group treated with 2% fulvic acid in comparison to the control group. This may have been associated with an increased digestive efficiency, with the food conversion ratio reducing from 2.4 to 1.9, and increased hepatopancreatic amylase, protease, and lipase enzyme activities. Enhanced activity of hemolymph superoxide dismutase was suggestive of an enhanced immune capacity, while hemolymph cell count increased by 16.4 and 13.6% in shrimp receiving diets supplemented with 1 and 2% fulvic acid, respectively. Additionally, the number of large granular cells increased by 37.3% and 40.8% relative to the control in these two groups. Furthermore, the lysozyme activity increased in shrimp receiving dietary supplementation of 1% and 2% fulvic acid by 16.7% and 24.7%, respectively. Phenol oxidase activity, which activates phagocytosis and encapsulation of invading pathogens, increased in all groups supplemented with fulvic acid, with the highest activity in the 1% fulvic acid group. Overall the present results suggest that fulvic acid is a promising feed additive for white-leg shrimp super-intensive culture.

Effect of Clostridium butyricum on intestinal microbiota and resistance to Vibrio alginolyticus of Penaeus vannamei

In order to evaluate the effect of Clostridium butyricum (C. butyricum) feeding on intestinal microorganisms and protection against infection by Vibrio alginolyticus (V. alginolyticus) in Penaeus vannamei (P. vannamei). We set up two groups, CG30 (fed normal feed) and CB30 (fed feed supplemented with C. butyricum), for the 30d C. butyricum feeding test, and four groups, CG (CG30 group injected with PBS), CB (CB30 group injected with PBS), VACG (CG30 group injected with V. alginolyticus), and VACB (CB30 group injected with V. alginolyticus), for the 24h infection test. The protective effect of C. butyricum against acute V. alginolyticus infection in P. vannamei was explained in terms of survival, histopathology, changes in enzyme activity, transcriptome analysis, and immune-related genes. We found that feeding C. butyricum significantly altered intestinal microbial populations' abundance and significantly reduced Vibrio spp. In the V. alginolyticus stress test, C. butyricum improved the survival rate and alleviated pathological changes in hepatopancreatic tissues, alleviated the reduction of superoxide dismutase (SOD) and phenoloxidase (PO) activity caused by infection, and increased the lysozyme content in P. vannamei. VACB group compared with the VACG group, 1730 up-regulated differentially expressed genes (DEGs) and 2029 down-regulated DEGs were screened. Quantitative real-time PCR (qRT-PCR) showed that dietary supplementation with C. butyricum suppressed the upregulation of alkaline phosphatase (AKP) transcription factors and the downregulation of prophenoloxidase (proPO), alpha-2-macroglobulin (A2M), and anti-lipopolysaccharide factor (ALF) induced by V. alginolyticus infection. In conclusion, feed supplementation with C. butyricum changed P. vannamei's population ratio of intestinal microorganisms. Moreover, C. butyricum has the potential to act as an inhibitor of V. alginolyticus infection and enhance the resistance of P. vannamei to V. alginolyticus infection.

White feces syndrome in Penaeus vannamei is potentially an Enterocytozoon hepatopenaei (EHP) associated pathobiome origin of Vibrio spp

White feces syndrome (WFS) is a commercially important disease in Penaeus vannamei (whiteleg shrimp) farming. The aetiology beyond the white or golden white midgut with mediocre growth performance producing a floating mass of white fecal strings in WFS-affected shrimp farms remains uncharted. To give WFS a perception of pathobiome, healthy P. vannamei shrimps were subjected to an enteric microsporidian Enterocytozoon hepatopenaei (EHP) infection along with Vibrio harveyi and V. alginolyticus in different combinations. Immune responses in haemolymph (total haemocyte count (THC), prophenoloxidase activity (proPO), respiratory burst activity (RBA), superoxide dismutase activity (SOD) and catalase activity (CAT)), plasma biochemical changes (aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP)) and digestive enzymes activity (alpha-amylase (AMY), lipase (LIP) and protease (PRO)) were assessed in the challenged shrimps at 5, 10 and 15 days post-infection (dpi). The microbial interactions between the EHP and Vibrio spp. have led to the formation of WFS in the challenged shrimps. The histological sections of the hepatopancreas revealed the presence of EHP along with colonized bacterial masses, leading to the formation of aggregated transformed microvilli (ATM) structures and increased sloughing of lipid vacuoles into the tubule lumen. A significantly decreased THC and increased proPO levels, dysregulated antioxidant system, prominent hepatic damage, reduced energy metabolism and higher lipid production were the key records supporting that EHP-associated WFS in P. vannamei is due to the pathobiome.

Protective Effects of Combined Utilization of Quercetin and Florfenicol on Acute Hepatopancreatic Necrosis Syndrome Infected Litopenaeus vannamei

This study aimed to determine the immunity, survival rate, and disease resistance of Litopenaeus vannamei treated using quercetin and florfenicol alone or in combination, after infection with acute hepatopancreatic necrosis syndrome caused by Vibrio parahaemolyticus (VPAHPND). After infection with VPAHPND, different types of feed were given to the shrimp for 5 days, including a control diet (drug-free), florfenicol only diet (15 mg/kg), quercetin only diet (400 mg/kg), a low-dose florfenicol/quercetin combined diet (200 mg/kg quercetin + 7.0 mg/kg florfenicol), a moderate-dose florfenicol/quercetin combined diet (400 mg/kg quercetin + 15 mg/kg florfenicol), and a high-dose florfenicol/quercetin combined diet (800 mg/kg quercetin + 30 mg/kg florfenicol). The cumulative mortality of shrimp was significantly reduced in the drug combination groups compared with either drug used alone (p < 0.05). The density of Vibrio was significantly lower and the immune parameters were significantly increased in the drug combination groups compared with either drug used alone (p < 0.05). Moreover, in the drug combination groups, the hepatopancreas tubules showed better integrity and structure compared with those when either drug was used alone. Therefore, compared with single drug treatment, the florfenicol and quercetin combination enhanced disease resistance, survival, and immune activity of VPAHPND-infected shrimp. When the combination treatment is used, the dosage of florfenicol can be reduced and a better therapeutic effect is obtained.

Cadmium and copper mixture effects on immunological response and susceptibility to Vibrio harveyi in white shrimp Litopenaeus vannamei

Cadmium (Cd2+) and copper (Cu2+) are considered immunotoxic metals and their presence in combination in the aquatic environment may cause effects on shrimp species as Litopenaeus vannamei. Thus, this research evaluates the combined effects of Cd2+ and Cu2+ on shrimp inoculated with Vibrio harveyi bacteria. The experiments were performed at 96-h of exposure to sublethal concentrations of both metals. No mortality was observed in organisms exposed to the sum of Criterion of Continuous Concentration (ΣCCC) in Cd + Cu mixture and those inoculated with V. harveyi. Higher clotting times were recorded in Cd + Cu + V. harveyi treatment at higher metal concentrations. No significant differences (P > 0.05) were recorded in hemocyanin content between shrimp exposed to metals and those experimentally infected. Significantly higher (P < 0.05) total hemocyte count (THC) was recorded at 96 h exposure in the ΣCCC and 10% treatments of Cd + Cu + V. harveyi experiment. Regarding Cd + Cu + V. harveyi bioassay, the highest phenoloxidase (PO) activity was recorded in shrimp inoculated with V. harveyi (0.326 ± 0.031 PO units/mg protein) at 96-h exposure. The lowest PO activity was observed in organisms exposed to Cd + Cu + V. harveyi. Regarding superoxide dismutase (SOD) activity, shrimp exposed to higher metal concentrations at 96 h showed the lowest hemolymph activity (6.03 ± 0.62 SOD units/mL). Protein decrease was observed in organisms exposed to metal mixture. The results showed that L. vannamei could be more susceptible to V. harveyi when exposed to Cd + Cu.

Biochemical indexes and gut microbiota testing as diagnostic methods for Penaeus monodon health and physiological changes during AHPND infection with food safety concerns

Severe shrimp disease outbreaks have a destructive impact on shrimp aquaculture and its associated downstream food processing industries. Thus, it is essential to develop proper methods for shrimp disease control, which emphasizes the importance of food safety. In this study, we performed biochemical tests and gut microbiome analysis using uninfected control and Vp AHPND-infected Penaeus monodon samples. Biochemical tests were performed to assess the phenoloxidase (PO) activity, respiratory Burst (RB) activity, nitrite concentration, superoxide dismutase (SOD) activity, total hemocyte count (THC), and total protein concentrations. Overall, upregulations were detected in these biochemical tests, which showed the activation of the immune response in P. monodon during acute hepatopancreatic necrosis disease (AHPND) infection, especially at 6 hpi and 12 hpi. Besides that, shrimp gut samples were collected and pooled (n = 3), followed by DNA extraction, PCR amplification targeting the V3/V4 16S ribosomal RNA (rRNA) region, next-generation sequencing (NGS), and bioinformatics analysis. Proteobacteria was the most abundant phylum in both samples. The Rhodobacteraceae family and Maritimibacter genus were proposed to be vital forshrimp health maintenance. Vp AHPND bacterial colonization and secondary Vibrio infections were postulated to have occurred based on the higher abundances of Vibrionaceae family and Vibrio genus in the Vp AHPND-infected sample. Firmicutes phylum together with Photobacterium and Aliiroseovarius genera were inferred to be pathogenic or related factors of AHPND infections. In conclusion, physiology (immune response activation) and gut microbiome changes of disease tolerant P. monodon during AHPND infection were identified. Both biochemical tests and 16S rRNA analysis are proposed as a combined strategy for shrimp health diagnosis for ensuring shrimp health maintenance, disease control, and food safety.

A Novel Disease (Water Bubble Disease) of the Giant Freshwater Prawn Macrobrachium rosenbergii Caused by Citrobacter freundii: Antibiotic Treatment and Effects on the Antioxidant Enzyme Activity and Immune Responses

The giant freshwater prawn, Macrobrachium rosenbergii, is an important and economical aquaculture species widely farmed in tropical and subtropical areas of the world. A new disease, "water bubble disease (WBD)", has emerged and resulted in a large loss of M. rosenbergii cultured in China. A water bubble with a diameter of about 7 mm under the carapace represents the main clinical sign of diseased prawns. In the present study, Citrobacter freundii was isolated and identified from the water bubble. The optimum temperature, pH, and salinity of the C. freundii were 32 °C, 6, and 1%, respectively. A challenging experiment showed that C. freundii caused the same typical signs of WBD in prawns. Median lethal dose of the C. freundii to prawn was 104.94 CFU/g. According to the antibiogram tests of C. freundii, florfenicol and ofloxacin were selected to evaluate their therapeutic effects against C. freundii in prawn. After the challenge with C. freundii, 86.67% and 72.22% survival of protective effects against C. freundii were evaluated in the oral florfenicol pellets and oral ofloxacin pellets feding prawns, respectively, whereas the mortality of prawns without fed antibiotics was 93%. After antibiotic treatment and C. freundii infection, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST), malondialdehyde (MDA), acid phosphatase (ACP), alkaline phosphatase (ALP), and lysozyme (LZM) in the hemolymph and hepatopancreas of the prawns and the immune-related gene expression levels of Cu/Zn-SOD, CAT, GPx, GST, LZM, ACP, anti-lipopolysaccharide factor, crustin, cyclophilin A, and C-type lectin in hepatopancreas were all significantly changed, indicating that innate immune responses were induced by C. freundii. These results can be beneficial for the prevention and control of C. freundii in prawns.

Physiological and antioxidant response of Litopenaeus vannamei against Vibrio parahaemolyticus infection after feeding supplemented diets containing Dunaliella sp. flour and β-glucans

The presence of pathogen agents in shrimp farming is the main obstacle for successful aquaculture. Vibrio species are naturally part of water because they play an important role as opportunistic bacteria. Vibrio parahaemolyticus was identified as the causative agent of the Early Mortality Syndrome in 2009, causing the loss of shrimp farming worldwide. Dunaliella sp. flour has been tested against Vibrio infection proving to be an effective prophylactic method that decreases mortality and improves physiological and immune response in Litopenaeus vannamei. Juvenile shrimp were exposed to 2% Dunaliella sp. flour and commercial 1.1% β -glucan diet provided every other day for 15 days and a posterior infection with V. parahaemolyticus (1 × 10⁶ CFU/mL). To evaluate shrimp stress status, some parameters as glucose, lactate, cholesterol, triglycerides, relative superoxide dismutase (SOD) gene expression and circulating hemocytes were analyzed in hemolymph at zero and seven days before infection and at 0, 24, and 48 h post-infection. L. vannamei fed with Dunaliella sp. showed 93% and β -glucan 87% survival, compared with 79% in the infected control group. Additionally, Dunaliella sp. improved hemocyte and lipid concentrations compared to β -glucan while both immunostimulants showed an increase in SOD response against bacteria. The addition of 2% Dunaliella sp. every other day in L. vannamei diet enhanced stress response against V. parahaemolyticus infection.

White shrimp Litopenaeus vannamei that have received mixtures of heat-killed and formalin-inactivated Vibrio alginolyticus and V. harveyi exhibit recall memory and show increased phagocytosis and resistance to Vibrio infection

Heat-killed Vibrio alginolyticus (HVa), formalin-inactivated V. alginolyticus (FVa), heat-killed Vibrio harveyi (HVh), formalin-inactivated V. harveyi (FVh), live V. alginolyticus (LVa), and live V. harveyi (LVh) were used in this study. White shrimp Litopenaeus vannamei receiving two mixtures (HVa + FVa) or four mixtures (HVa + FVa + HVh + FVh) served as primary exposure, and shrimp receiving LVa or LVh afterward served as secondary exposure. Shrimp receiving marine saline and then receiving either LVa or LVh served as controls. Phagocytic activity and clearance efficiency were examined in shrimp that received two mixtures after 1-8 weeks and then received LVa. Both the phagocytic activity and clearance efficiency of shrimp receiving two mixtures were significantly higher than in control shrimp after 1-8 weeks. In another experiment, phagocytic activity and clearance efficiency were examined in shrimp that received four mixtures after 1-8 weeks and then received LVa and LVh, respectively. The phagocytic activity of shrimp receiving four mixtures was significantly higher than in control shrimp after 1-8 weeks post exposure to LVa and LVh. The clearance efficiency of shrimp receiving four mixtures was significantly higher than in control shrimp after 1-6 weeks post exposure to LVa, and 1-7 weeks post exposure to LVh. In the other experiment, the survival rate of shrimp that received four mixtures after five weeks were challenged with LVa at 6.4 × 10⁷ colony-forming units (cfu) shrimp^-1 and LVh at 4.4 × 10⁶ cfu shrimp^-1. Shrimp that received marine saline for five weeks and then challenged with LVa and LVh at a same dose served as challenged controls. The survival rate of shrimp that received four mixtures was significantly higher (90%) than that of control shrimp (67%), and significantly higher (73%) than that of control shrimp (53%) after 3-7 days post challenge with LVa and LVh. It is concluded that the mixtures have feature of adjuvant and antigen, and shrimp receiving mixtures of heat-killed and formalin-inactivated V. alginolyticus and V. harveyi even after 5-8 weeks exhibit memory recall and show increased phagocytosis and resistance to Vibrio infections.

Effects of Vibro harveyi and Staphyloccocus aureus infection on hemocyanin synthesis and innate immune responses in white shrimp Litopenaeus vannamei

Hemocyanin, a multifunctional oxygen-carrying protein, has critical effects on immune defense in crustaceans. To explore the role of hemocyanin in anti-pathogen mechanism, effects of Vibrio harveyi (V. harvey) and Staphyloccocus aureus (S. aureus) on hemocyanin synthesis and innate immune responses were investigated in Litopenaeus vannamei (L. vannamei) during infection in vivo. Results showed that 10⁵ and 10⁶ cells mL^-1V. harveyi and 10⁶ cells mL^-1S. aureus significantly affected plasma hemocyanin concentration, hepatopancreas hemocyanin mRNA and subunits expressions, plasma phenol oxidase (PO), hemocyanin-derived PO (Hd-PO), antibacterial, and bacteriolytic activities during the experiment under bacterial stress, while these parameters did not change remarkably in control group. The concentration of hemocyanin in plasma fluctuated, with a minimum at 12 h and a maximum at 24 h. Moreover, the expression of hemocyanin mRNA peaked at 12 h, while the level of hemocyanin p75 and p77 subunits reached maximum at 24 h. Besides, plasma PO and Hd-PO activities peaked at 24 h, and antimicrobial and bacteriolytic activities peaked at 12 h and 24 h, respectively. In addition, 10⁵ cells mL^-1S. aureus had no significant effect on the synthesis of hemocyanin and prophenoloxidase activating (pro-PO) system, but significantly increased antimicrobial activity at 12 h and bacteriolytic activity at 24 h. Therefore, these results suggest that the hemocyanin synthesis was initiated after invasion of pathogen, and the newly synthesized hemocyanin, acted as an immune molecule, can exerts PO activity to regulate the immune defense in L. vannamei in vivo.

Survival and immune response of white shrimp Litopenaeus vannamei following single and concurrent infections with WSSV and Vibrio parahaemolyticus

The survival and immune responses of Litopenaeus vannamei were evaluated during white spot syndrome virus (WSSV) or Vibrio parahaemolyticus single and concurrent infections. The mortality, WSSV load, activities of 4 immune enzymes: acid phosphatase (ACP), alkaline phosphatase (AKP), peroxidase (POD) and superoxide dismutase (SOD), and the transcription of Evolutionarily Conserved Signaling Intermediate in Toll pathways of L.vannamei (LvECSIT) were quantified at 0, 3, 6, 12, 24, 48, 72 and 96 h post-infection (pi). The results showed: (i) the cumulative mortality of the co-infection group (WSSV and V. Parahaemolyticus 83%) was significantly lower than the WSSV infection group (97%) (P < 0.05) at 96 hpi; (ii) copies of WSSV in the co-infection group were significantly lower than that of the single infection group from 24 to 96 hpi (P < 0.05); (iii) ACP, AKP,POD and SOD activity in the gills of the co-infection group was higher than that of the WSSV group at12, 48 and 96 hpi (P < 0.05).The expression of LvECSIT mRNA in the co-infection group was significantly higher than in the WSSV infection group from 12 to 72 hpi (P < 0.05).The results indicate that proliferation of WSSV is inhibited by V.parahaemolyticus infection. In addition, infection with WSSV alone causes a significant reduction in some immune responses of shrimp than co-infection with WSSV and V.parahaemolyticus occurs at 26 °C. Third, LvECSIT, an essential member of TLR signaling pathway might play a crucial role in shrimp defense against WSSV - Vibrio co-infection.

Effectiveness of traditional Chinese herbal medicine, San-Huang-San, in combination with enrofloxacin to treat AHPND-causing strain of Vibrio parahaemolyticus infection in Litopenaeus vannamei

The effects of oral administration of enrofloxacin (ENR) and San-Huang-San (SHS), singly or in combination, on the survival performance, disease resistance, and immunity of Litopenaeus vannamei were investigated. After challenge with an AHPND-causing strain of Vibrio parahaemolyticus (VP_AHPND), shrimp were immediately fed a drug-free diet, diets containing only ENR (20 mg·kg^-1) or SHS (500 mg·kg^-1) or diets containing low-dose (10 mg·kg^-1 ENR + 250 mg ·kg^-1 SHS), medium-dose (20 mg·kg^-1 ENR + 500 mg ·kg^-1 SHS), and high-dose (40 mg·kg^-1 ENR + 1000 mg ·kg^-1 SHS) drug combinations for 5 days. The cumulative shrimp mortality over 5 days after injection of VP_AHPND in the ENR + SHS combination groups was significantly lower than that in the ENR or SHS alone groups (p < 0.05). Immune parameters, including the vibrio density, total hemocyte counts (THCs), hemocyanin (HEM) concentration, antibacterial activity, activity levels of lysozyme (LZM), acid phosphatase (ACP), alkaline phosphatase (AKP), and phenoloxidase (PO) in cell-free hemolymph, and the expression levels of the immune-related genes anti-lipopolysaccharide factor (ALF), cathepsin B (catB), crustin, lectin (Lec), lysozyme (LZM), and Toll-like receptor (TLR) in hemocytes were determined in the shrimp. The results showed that the shrimp in drug combination groups cleared more VP_AHPND than that in the ENR or SHS group in the same time. The values for other immune parameters in the drug combination groups were higher than those in the ENR or SHS group (p < 0.05). Finally, in the histological examinations, the histological structural alignment and integrity of the hepatopancreatic tubules in the drug combination groups were better than that in the ENR and SHS groups. Under the experimental conditions, compared with ENR or SHS used alone, the combination use of ENR and SHS could improve immunity and disease resistance in shrimp after VP_AHPND infection, and could reduce the use of ENR when the better therapeutic effect was achieved.

Evaluation of combination effects of Astragalus polysaccharides and florfenicol against acute hepatopancreatic necrosis disease-causing strain of Vibrio parahaemolyticus in Litopenaeus vannamei

The effects of oral administration of Astragalus polysaccharides (APS) and florfenicol (FFC), singly or in combination, on the survival performance, disease resistance, and immunity of Litopenaeus vannamei were investigated. After challenge with an AHPND-causing strain of Vibrio parahaemolyticus (VP_AHPND), shrimp were immediately fed a drug-free diet, diets containing only APS (200 mg·kg^-1) or FFC (15 mg·kg^-1), or diets containing low-dose (7.5 mg·kg^-1 FFC + 100 mg·kg^-1 APS), medium-dose (15 mg·kg^-1 FFC + 200 mg·kg^-1 APS), and high-dose (30 mg·kg^-1 FFC+400 mg·kg^-1 APS) drug combinations for 5 days. The cumulative shrimp mortality over 5 days after injection of VP_AHPND in the APS + FFC combination groups was significantly lower than that in the APS or FFC alone groups (p < 0.05). Immune parameters, including the total hemocyte counts (THCs), hemocyanin (HEM) concentration, antibacterial activity, activity levels of lysozyme (LZM), and levels of acid phosphatase (ACP), alkaline phosphatase (AKP), and phenoloxidase (PO) in cell-free hemolymph, and the expression levels of the immune-related genes anti-lipopolysaccharide factor (ALF), cathepsin B (catB), crustin, lectin (Lec), lysozyme (LZM), and Toll-like receptor (TLR) in hemocytes and hepatopancreas were determined in the shrimp. The values for these immune parameters in the drug combination groups were higher than those in the APS or FFC group (p < 0.05). Finally, in the histological examinations, the histological structural alignment and integrity of the hepatopancreatic tubules in the drug combination groups was better than that in the APS and FFC groups. Under the experimental conditions, dietary APS and FFC had a synergistic effect on immunity and disease resistance among shrimp after VP_AHPND infection.

Molecular characterization and function analysis of a nucleotide excision repair gene Rad23 from Litopenaeus vannamei after Vibrio alginolyticus challenge

Nucleotide excision repair (NER) removes many different types of DNA lesions, and NER related host factors are reported to aid recovery steps during viral integration. Here, we report the identification and characterization of a DNA repair gene Rad23 from Litopenaeus vannamei and explore its role in innate immunity of crustaceans. LvRad23 contains a1149 bp open reading frame (ORF) which encodes a 382 amino acids protein with predicted theoretical isoelectric point of 4.21. LvRad23 was ubiquitously expressed in the muscle, eyestalk, gill, stomach, heart, legs, intestine, and hepatopancreas in order from high to low and LvRad23 protein was showed to be located in the cytoplasm of Drosophila S2 cells. The homology analysis showed that it has a high sequence homology with Rad23 protein from Marsupenaeus japonicus. Vibrio alginolyticus challenge induced a remarkable up-regulation of LvRad23 mRNA in hepatopancreas. Knocking down LvRad23can interfere the NER pathway by down regulating the expression of replication protein A (RPA) and proliferating cell nuclear antigen (PCNA). However it didn't cause any significant difference on total hemocyte count (THC) between LvRad23-silenced and non-silenced group.LvRad23-silenced then challenge with V. alginolyticus inducing high level of reactive oxygen species (ROS) and DNA damage in hemolymph. As well as decreased THC, which seriously diminished the innate immune system of L. vannamei. Meanwhile, the NER pathway was reactived by enhancing the expression of LvRad23 and promoting the production of LvPCNA to resist apoptosis and maintain proliferation of hemolymph cells in the later stage. Our results suggest that LvRad23 plays a vital role in shrimp specific immune response to V. alginolytcus through its participation in NER pathway.

Identifying the function of LvPI3K during the pathogenic infection of Litopenaeus vannamei by Vibrio alginolyticus

It is well known that PI3K regulates various processes in mammalian cells by generating a secondary messenger that later activates AKT. However, its innate immune function in crustaceans remains unclear. We report the characterization of Litopenaeus vannamei PI3K (LvPI3K) for investigating how PI3K participates in the innate immunity of crustaceans. Full-length LvPI3K cDNA was 3357 bp long, with a 3222 bp open reading frame (ORF) that encodes a putative protein of 1292 amino acids. The PI3K catalytic domain (PI3Kc) of LvPI3K was found to be rather conserved when the PI3Ks from other species were analyzed. The LvPI3K protein was shown to be localized to the cytoplasm of Drosophila S2 cells, while LvPI3K mRNA was ubiquitously expressed in healthy L. vannamei, with the highest expression found in hemolymph. A dual luciferase reporter gene assay demonstrated that LvPI3K overexpression activated the promoter of antibacterial peptide LvPEN4 in a dose-dependent manner. However, the addition of PDTC, a specific inhibitor of NF-κB, suppressed the LvPI3K-induced LvPEN4 promoter activation. Moreover, Vibrio alginolyticus challenge induced a rapid up-regulation of LvPI3K expression. Further experiments showed that LvPI3K silencing in shrimp challenged with V. alginolyticus significantly increased Vibrio number, ROS production and DNA damage in the hemolymph, as well as significantly decreased total hemocyte count. The mRNA levels of certain molecules related to LvPI3K signaling, such as LvAKT and LvPEN4, also decreased following LvPI3K silencing. Taken together, these results suggest that LvPI3K regulates the downstream signal component LvPEN4 and functions in V. alginolyticus resistance.

Immune response of Exopalaemon carinicauda infected with an AHPND-causing strain of Vibrio parahaemolyticus

To investigate the immune response of Exopalaemon carinicauda infected with an AHPND-causing strain of Vibrio parahaemolyticus (VP_AHPND), three-generation breeding of shrimp selected for their survival to VP_AHPND infection was applied to explore the relationship between immune parameters and AHPND-resistant capacity of E. carinicauda. In this study, the LD₅₀ dose of 48 h and survival rates at 144 h of shrimp to VP_AHPND increased from 10^6.0 to 10^6.6 cfu ml^-1 and from 26.67% to 36.67% by three successive generations selection, respectively, while there was no significant difference between the first and second generation (p > .05). Then the immune parameters including vibrio density, total hemocyte counts (THCs), hemocyanin (HEM) concentration, antibacterial activity, activities of four immune enzymes, and expressions of eight immune-related genes were determined in the shrimp of the first (G1) and the third selective generation (G3). The results showed that the shrimp in G1 and G3 generation cleared most of VP_AHPND infecting hepatopancreas during 24 h and 6 h post injection, respectively. The levels of THCs, HEM concentration, antibacterial activity, immune enzymes including lysozyme (LZM) activity, alkaline phosphatase (AKP) activity in cell-free hemolymph, and the expression levels of Tollip, ALF, cathepsin B in hemocytes and hepatopancreas, crustin, LZM, SR in hepatopancreas and LGBP in hemocytes were higher in G3 generation than in G1 generation after infection with VP_AHPND, suggesting that these parameters may serve as potential disease-resistant indicators for evaluating the physiological status and disease-resistant capability of shrimp when infected with VP_AHPND. To further test the role of above genes in the shrimp immune response, RNAi was used to suppress their expressions and a significant decrease in survival was observed in knockdown shrimp infected with VP_AHPND as compared to controls.

Flow cytometic analysis of Penaeus monodon haemocyte responses to poly I:C

This study was aimed at investigating the cellular responses of Penaeus monodon haemocytes to poly I:C stimulation using flow cytometric assay. Total haemocyte count (THC), percentages of different haemocyte subpopulations [hyaline cells (HC), semigranular cells (SGC) and granular cells (GC)], non-specific esterase activity (EA), total reactive oxygen species/reactive nitrogen species (ROS/RNS) production, nitric oxide (NO) production, apoptotic haemocyte ratio and plasmic phenoloxidase (PO) activity were determined in poly I:C-injected shrimp. Results showed that poly I:C at a low dose (5 μg shrimp^-1) caused obvious increases in THC, GC proportion, ROS/RNS production and NO production, but had no significant effect on EA, apoptosis and PO activity. In the early stage of poly I:C injection at a high dose (20 μg shrimp^-1), THC and GC proportion improvements could also be observed, suggesting that GC might be induced to release from hemocytopoietic or other tissues to participate in immune response, and this subpopulation might be the main cell type involved in the cellular defence against virus. In the later period, proportions of both GC and SGC reduced paralleled by THC reduction, indicating that depletion of GC and SGC was mainly contributed to the reduced count of circulating haemocyte. Obvious increases in ROS/RNS production and NO production were induced in haemocyte of shrimp under a high dose of poly I:C stimulation, but only slight rise of EA and suppression of PO activity could be observed in poly I:C-stimulated shrimp, suggesting that ROS/RNS-dependent system was vital in the immune defence of shrimp against virus. On the other hand, increase of apoptotic haemocyte ratio and THC reduction were presented after the drastic increases of ROS/RNS and NO productions, implying that the stimulated ROS/RNS might be excess and harmful, and was the major factor for the haemocyte apoptosis and depletion. THC recovered after 48 h injection, while haemocyte apoptosis also returned to the control level, suggesting that apoptosis might be contributed to eliminate damaged, weak or infected haemocytes to renew the circulating haemocytes, and it could be considered as an important defending strategy against virus.

Various cellular responses of different shrimp haemocyte subpopulations to lipopolysaccharide stimulation

Different haemocyte types have been reported to play diverse roles in immune defense of shrimp. To investigate the roles of the three haemocyte types [hyaline cells (HC), semigranular cells (SGC) and granular cells (GC)] of shrimp in immune responses against lipopolysaccharide (LPS), percentage, non-specific esterase activity (EA), reactive oxygen species (ROS) production and nitric oxide (NO) production of the three haemocyte subpopulations were analyzed in LPS-injected Penaeus monodon using flow cytometry. Results showed that percentage of HC increased after 3 h injection, and returned to the original level after 48 h. Proportion of SGC and GC reduced after 6-36 h and 3-12 h respectively, and recovered to the initial level after 48 and 24 h respectively. Loss of SGC and GC might be related to degranulation to release proPO system, and degranulation of GC seemed more sensitive to LPS stimulation. EA of both HC and SGC improved after 3-6 h injection, while EA of GC was induced after 3-24 h. No significant effect of LPS injection could be found in ROS production and NO production of HC. Enhanced ROS levels was observed in SGC and GC after 3-24 h and 3-36 h respectively, and NO production of SGC and GC improved after 3-48 h injection. These results demonstrated that SGC and GC possessed strong capabilities for LPS-induced EA, ROS production and NO production, while HC only displayed EA response to LPS, suggesting that GC and SGC play the main role in immune defense of shrimp against Gram-negative bacteria.

Molecular cloning, characterization and function of a germinal center kinase MST4 gene from Litopenaeus vannamei in response to Vibrio alginolyticus challenge in TLR-TRAF6 signaling pathway

The serine/threonine protein kinase MST4 plays multiple roles in the regulation of signaling pathways that govern cellular processes including mitosis, migration, homeostasis, polarity, proliferation, differentiation and apoptosis. Here we report the identification and characterization of the full-length sequence of LvMST4 from the shrimp L. vannamei, and investigations into its role in the shrimp's immune response to infection by the pathogenic bacterium Vibrio alginolyticus. Subcellular localization assays demonstrated the enzyme's presence in the shrimp's cytoplasm, and tissue-specific expression analysis revealed that it is expressed ubiquitously but at different levels in different tissues. Infection with V. alginolyticus increased LvMST4 expression and induced a rapid response via the TLR-TRAF6 signaling pathway, causing a decline in the total hemocyte count (THC) and an increase in respiratory burst (RB) activity. In non-infected shrimp, RNAi silencing of LvMST4 with dsRNA had no significant effect on THC but seemed to activate the TRAF6-MKK6-p38 pathway and reduced RB activity. In shrimp challenged with V. alginolyticus, LvMST4 silencing reduced bacterial clearance and increased the initial upregulation of LvTRAF6 while reducing the expression of LvMKK6 and Lvp38. LvMST4 silencing also slightly reduced the THC but caused pronounced increases in RB activity and cumulative mortality. These findings suggest that LvMST4 contributes to antimicrobial responses via the TLR-TRAF6 signal pathway, and helps maintain immunological homeostasis in L. vannamei.

Pathogenicity profile of Vibrio parahaemolyticus in farmed Pacific white shrimp, Penaeus vannamei

A pathobiological study was conducted using Vibrio parahaemolyticus (V_P) strain isolated from vibriosis affected shrimp (Penaeus vannamei) farms in Kancheepuram and Thiruvallur districts of Tamil Nadu during August 2014 to February 2015. The isolate was identified based on the morphological, physiological, biochemical and molecular characters. LD₅₀ value with intramuscular injection was determined as 2.6 × 10⁴ cfu/shrimp and sequential pathology was studied giving 6.1 × 10³ cfu/shrimp (LD₂₅). Total plate count (TPC) and total Vibrio count (TVC) in water, pond sediment, haemolymph, muscle, HP and gut were found significantly (P < 0.01) higher in natural cases than the experimental set up. Clinical signs and lesions observed in the natural and experimental cases were anorexia, lethargy, cuticle softening, loose shells, abdominal muscle cramp, red discoloration, opaque and whitish abdominal and tail musculature, necrosis of exoskeleton or splinter burns, reddish pleural borders of antennae, uropods and telson, swollen tail fan, ulcers, moribund shrimp sinking to bottom, and mortalities with shrunken discoloured HP with empty gut. Total haemocyte count (THC), small nongranular haemocyte (SNGH), large nongranular haemocyte (LNGH), small granular haemocyte (SGH) and large granular haemocyte (LGH) counts lowered significantly (P < 0.01) at 3, 6, 12, 24, 48, 96 and 192 h post injection (p.i). No LGH were found after 96 h of challenge. The post injection qPCR analyses of haemocytes showed up-regulations of penaeidin-3a, lysozyme, prophenoloxidase I, prophenoloxidase II and serine protein at 3 and 6 h of infection. There was total down-regulation of crustin from 3 to 192 h p.i. There was a remarkable elevation in the level of proPO I with concomitant depletion of proPO II. The pattern of up- and down-regulations in proPO I and SP were similar. The post infection qPCR analyses showed that these immune related genes could be used as markers for assessing the immune status of P. vannamei. Major histopathological manifestations observed were haemocyte infiltration/nodule in the epidermis, skeletal and cardiac muscles, atrophy of the excretory organ, and disrupted HP tubules with diffuse interstitial edema and haemocytic infiltration. Further HP showed that there was thickening of intertubular space, karyomegaly with prominent nucleoli, rounding and sloughing of HP tubular epithelium, many mitotic figures with bacterial colonies and apoptotic bodies, separation of shrunken tubule epithelium from myoepithelial fibers, regeneration of tubules, cystic, dilated and vacuolated appearance of HP tubules, hypoplastic changes in the tubules with no B, R and F cells, granuloma formation, concretions in tubules, calcification, necrosis, and washed out appearance with complete loss of architecture. The progression of the degenerative changes in the HP tubular epithelial cells was from proximal to distal end. In haematopoietic organ, increased mitotic activities with focal to extensive depletion and degeneration were observed. Degeneration of the stromal matrix with spheroid formation in lymphoid organ was observed among the Vp infected natural and experimental animals. Degeneration of glandular structures in the prehensile appendages with bacterial colonies, melanization and loss of epithelial layer in oesophagus, swelling and loss of architecture with mucinous secretion in the stomach, degeneration of peritrophic membrane in the lumen of intestine were observed in field cases but not in the experimental studies. Further, this study established the pathobiology of the Vp isolate to P. vannamei.

White shrimp Litopenaeus vannamei that have received fucoidan exhibit a defense against Vibrio alginolyticus and WSSV despite their recovery of immune parameters to background levels

White shrimp Litopenaeus vannamei receiving fucoidan at 2, 6, and 10 μg g^-1 after 0-144 h or 0-120 h were examined for immune parameters (haemograms, phenoloxidase activity, respiratory burst, and superoxide dismutase activity), proliferation of haemocyte in the haematopoietic tissue (HPT), gene expression, and phagocytic activity and clearance efficiency to Vibrio alginolyticus. Immune parameters and mitotic index of HPT increased after 3-24 h, reached their maxima after 48-72 h, and returned to background values after 144 h. Transcripts of lipopolysaccharide and β-1,3-glucan binding protein (LGBP), peroxinectin (PX), prophenoloxidase (proPO) I, proPO II, astakine, and haemocyte homeostasis-associated protein (HHAP) were up-regulated to a maximum after 48-72 h and returned to background values after 144 h. Phagocytic activity and clearance efficiency to V. alginolyticus increased after 12 h, reached its maximum after 48 h, and continued to remain higher after 120 h. In another experiment, shrimp receiving fucoidan after 48 h and 144 h were respectively challenged with V. alinolyticus at 6 × 10⁶ colony-forming units (cfu) shrimp^-1 or challenged with WSSV at 1.2 × 10⁵ copies shrimp^-1 and then placed in seawater. The survival rate of shrimp receiving fucoidan was significantly higher than in controls. In conclusion, shrimp receiving fucoidan showed a proliferation of HPT, increased immune parameters, and up-regulated transcripts of LGBP, PX, proPO I, proPO II, astakine, and HHAP after 48 h. Shrimp receiving fucoidan exhibited a defense against V. alginolyticus and WSSV, even after immune parameters recovered to background levels.

Cloning and characterization of tyrosine hydroxylase (TH) from the pacific white leg shrimp Litopenaeus vannamei, and its expression following pathogen challenge and hypothermal stress

Tyrosine hydroxylase (TH) belongs to the biopterin-dependent aromatic amino acid hydroxylase enzyme family, and it represents the first and rate-limiting step in the synthesis of catecholamines that are required for physiological and immune process in invertebrates and vertebrates. Cloned Litopenaeus vannamei TH (LvTH), containing a short alpha helix domain, a catalytic core, a regulatory domain, a phosphorylation site and two potential N-linked glycosylation sites as presented in vertebrate and insect THs without acidic region and signal peptide cleavage sites at the amino-terminal, exhibited a similarity of 60.0-61.2% and 45.0-47.0% to that of invertebrate and vertebrate THs, respectively. Further, LvTH expression was abundant in gill and haemocytes determined by quantitative real-time PCR. L. vannamei challenged with Vibrio alginolyticus at 10(5) cfu shrimp(-1) revealed significant increase of LvTH mRNA expression in haemocytes within 30-120 min and in brain within 15-30 min followed with recuperation. In addition, shrimps exposed to hypothermal stress at 18 °C significantly increased LvTH expression in haemocytes and brain within 30-60 and 15-60 min, respectively. The TH activity and haemolymph glucose level (haemocytes-free) significantly increased in pathogen challenged shrimp at 120 min and 60 min, and in hypothermal stressed shrimp at 30-60 and 30 min, respectively. These results affirm that stress response initiates in the brain while haemocytes display later response. Further, the significant elevation of TH activity in haemolymph is likely to confer by TH that released from haemocytes. In conclusion, the cloned LvTH in our current study is a neural TH enzyme appears to be involved in the physiological and immune responses of whiteleg shrimp, L. vannamei suffering stressful stimulation.

Cellular responses of the tiger shrimp Penaeus monodon haemocytes after lipopolysaccharide injection

This study was aimed at investigating the in vivo effects of lipopolysaccharide (LPS) injection on Penaeus monodon haemocytes at a cellular level. Cellular responses of LPS-injected shrimp were analysed using flow cytometry. Results showed that LPS injection caused total haemocyte count (THC) and count of large cells (semigranular and granular cells) decline. In LPS-injected shrimp, percentage of large cells decreased at the initial stage, and returned to the original level later. After LPS infection, non-specific esterase activity, reactive oxygen species (ROS) production and nitric oxide (NO) production in haemocytes were significantly induced, while apoptotic cell ratio of haemocytes increased. PO activity in plasma increased in shrimp received LPS at 2 μg g(-1) after 3-12 h and at 8 μg g(-1) after 3-6 h, and then returned to the initial levels. These results demonstrated that LPS induced immune responses on haemocytes, including production of ROS and NO, and release of esterase and PO. On the other hand, THC reduction might be due to the ROS/NO-induced apoptosis. Haemocyte apoptosis which would eliminate damaged or weak cells and contribute to haemocyte renewal, may be a defending strategie against pathogens.

Molecular characterization and function of a PTEN gene from Litopenaeus vannamei after Vibrio alginolyticus challenge

PTEN, a tumor suppressor gene, suppresses cell survival, growth, apoptosis, cell migration and DNA damage repair by inhibiting the PI3K/AKT signaling pathway. In this study, the full-length Litopenaeus vannamei PTEN (LvPTEN) cDNA was obtained, containing a 5'UTR of 59bp, an ORF of 1269bp and a 3'UTR of 146bp besides the poly (A) tail. The PTEN gene encoded a protein of 422 amino acids with an estimated molecular mass of 48.3 KDa and a predicted isoelectric point (pI) of 7.6. Subcellular localization analysis revealed that LvPTEN was distributed in both cytoplasm and nucleus, and the tissue distribution patterns showed that LvPTEN was ubiquitously expressed in all the examined tissues. Vibrio alginolyticus challenge induced upregulation of LvPTEN expression. Moreover, RNAi knock-down of LvPTEN in vivo significantly increased the expression of LvAKT mRNA, while reducing that of the downstream apoptosis genes LvP53 and LvCaspase3. LvPTEN knock-down also caused a sharp increase in cumulative mortality, bacterial numbers, and DNA damage in the hemolymph of L. vannamei following V. alginolyticus challenge, together with a sharp decrease in the total hemocyte count (THC). These results suggested that LvPTEN may participate in apoptosis via the PI3K/AKT signaling pathway in L. vannamei, and play an important role in shrimp innate immunity.

The GRIM-19 plays a vital role in shrimps' responses to Vibrio alginolyticus

GRIM-19 (gene associated with retinoid-interferon-induced mortality 19), a novel cell death regulatory gene, plays important roles in cell apoptosis, mitochondrial respiratory chain and immune response. It has been reported to interact physically with STAT3 and inhibit STAT3-dependent signal transduction. In this study, a new GRIM-19 gene, which is a 789-bp gene encoding a 149 amino acids protein, is identified and characterized from Litopenaeus vannamei. The tissue distribution patterns showed that LvGRIM-19 was widely expressed in all examined tissues, with the highest expression in muscle. Quantitative real-time PCR revealed that LvGRIM-19 was down-regulated in hepatopancreas after infection with the Vibrio alginolyticus. Knockdown of LvGRIM-19 by RNA interference resulted in a lower mortality of L. vannamei under V. alginolyticus infection, as well as an enhancement in the protein expression of STAT gene and JAK gene. V. alginolyticus infection caused an increase apoptotic cell ratio and ROS production of L. vannamei, while LvGRIM-19 silenced shrimps showed significantly lower than GFP group. Our results suggest that the GRIM-19 plays a vital role in shrimps' responses to V. alginolyticus. Interferenced LvGRIM-19 treatment during V. alginolyticus infection could increase 12 h survival rate, which might indicated that LvGRIM-19 is closely related to death of shrimps.

Roles of receptor for activated protein kinase C1 for modulating immune responses in white shrimp Litopenaeus vannamei

Complementary (c)DNA encoding a receptor for activated protein kinase C1 (RACK1) messenger (m)RNA of the white shrimp Litopenaeus vannamei, designated LvRACK1, consisted a 1136-bp cDNA containing an open reading frame (ORF) of 954 bp, a 111-bp 5'-untranslated region (UTR), and a 71-bp 3'-UTR, which is a 36 kDa cytosolic protein, belonging to the Trp-Asp40 (WD40) family of proteins, characterized by containing seven highly conserved Trp-Asp40 (WD40) internal repeats, and a poly A tail. The WD repeat of LvRACK1 can be predicted to form a seven-bladed propeller structure with each WD repeat composed of four antiparallel β-sheets. The WD40 domains have been implicated in protein-protein interactions. A comparison of amino acid sequences showed that LvRACK1 was closely related to arthropods RACK1. LvRACK1 cDNA was synthesized in all tested tissues detected with real-time PCR including haemocytes, hepatopancreas, gills, muscles, subcuticular epithelium, intestines, abdominal nervous ganglia, thoracic nervous ganglia, lymphoid organ, stomach, heart, and antennal gland, especially in subcuticular epithelium and gill. LvRACK1 mRNA transcription in haemocytes of L. vannamei injected with Vibrio alginolyticus decreased. The depletion of LvRACK1 of haemocytes in L. vannamei received its dsRNA revealed the increased respiratory bursts per haemocyte, superoxide dismutase (SOD), activity, glutathione peroxidase (GPx) activity, and clotting time, but showed the decreased total haemocyte count (THC), hyaline cells (HCs), phagocytic activity, and transglutaminase (TG) activity. LvRACK1 silenced shrimp showed the upregulated gene expressions of cyMnSOD, mtMnSOD, peroxinectin (PE), and TGI, and showed the downregulated α2-macroglobulin (α2-M), clottable protein (CP), lysozyme, and crustin gene expressions. It is therefore concluded that LvRACK1 is involved in immune defense and signaling transduction in haemocytes of L. vannamei infected with V. alginolyticus.

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.

Oxidative stress response of the black tiger shrimp Penaeus monodon to Vibrio parahaemolyticus challenge

Vibrio parahaemolyticus is a virulent pathogen that affects shrimp aquaculture. Reactive oxygen species are produced by the immune system that defends the host against foreign microorganisms. In the present study, the oxidative stress response in hepatopancreas and gills of Penaeus monodon to V. parahaemolyticus challenge were studied, such as respiratory burst, ROS production (·O2(-) and ·OH), activities of antioxidant enzymes (CAT, GPx, SOD, POD and GST) and oxidative damage to lipid and protein (indexed by contents of MDA). Compared with the control group, after V. parahaemolyticus challenge, respiratory burst and ROS production were up-regulated significantly. GPx and POD activity increased significantly in hepatopancreas and gills of the shrimps at 12 h, but CAT activity decreased markedly at 12 h and 24 h. SOD and GST activity in hepatopancreas of the shrimps increased significantly at 1.5 h, but decreased markedly at 12 h-48 h. MDA content increased significantly after 6 h-24 h challenge. HE staining showed that V. parahaemolyticus challenge induced damage symptoms in hepatopancreas of P. monodon. Our study revealed that V. parahaemolyticus influenced the antioxidative status and caused oxidative stress and tissue damage via confusion of antioxidant enzymes in P. monodon.

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.

The impact of Aeromonas salmonicida infection on innate immune parameters of Atlantic salmon (Salmo salar L)

Enzyme activities and gene expression of a number of innate immune parameters in the serum, mucus and skin of Atlantic salmon (Salmo salar) were investigated after challenge with a pathogenic strain of Aeromonas salmonicida (A. salmonicida). Fish were injected in the dorsal muscle with either 100 μl bacterium solution, about 3.05 × 10(7) CFU/ml A. salmonicida, or 100 μl 0.9% NaCl (as control group) and tissue samples were collected at days 0, 2, 4 and 6 post-injection. Lysozyme (LSZ) and alkaline phosphatase (AKP) activities in serum, mucus and skin, and LSZ and AKP mRNA expression in skin of the challenged fish were higher than those of the control at most of the experimental time, with significant differences at several time points (P < 0.05), indicating the involvement of LSZ and AKP in the innate immunity of Atlantic salmon to A. salmonicida. Superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in mucus and skin, along with the SOD, POD and CAT mRNA expression in skin significantly decreased at day 4 and 6, indicating the decreased antioxidant capacity of the challenged fish. Glutamate pyruvate transaminase (GPT) and glutamic oxalacetic transaminase (GOT) activities in serum, mucus and skin of the challenged group were all higher than those of the control after the injection, and at several time points significant differences were found between the two groups, suggesting organs of fish were impaired after the pathogen infection. The changes of the GPT and GOT activities could be used as potential biomarkers for the impairment of physiological functions caused by the pathogen infection. Identified biomarkers of the immune responses will contribute to the early-warning system of the disease. So this study will not only provide a theoretical basis for vaccine development, but also provide basic data for the establishment of early warning systems for diseases caused by A. salmonicida in Atlantic salmon rearing.

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.

Identification of novel copper/zinc superoxide dismutase (Cu/ZnSOD) genes in kuruma shrimp Marsupenaeus japonicus

Superoxide dismutases (SODs) protect cells from superoxides, but in invertebrates, they also have role in the innate immune system. In this study, the genes for five isoforms of copper/zinc superoxide dismutase (MjCu/ZnSOD) gene were identified and sequenced in kuruma shrimp, Marsupenaeus japonicus. The coding parts of the genes ranged from 516 to 585 bp in length and encoded from 172 to 194 amino acids. Structure, phylogenetic and BLAST analyses indicated that MjCu/ZnSOD isoform_3 and _5 belonged to extracellular Cu/ZnSOD (ecSOD) group while the other three isoforms belong to the intracellular Cu/ZnSOD family. In healthy shrimp, the highest expressions of isoform 2, 3 and 4 were in the gills, whereas the expression of isoform 5 was highest in hemocytes. Challenging the shrimp with WSSV and Vibrio penaeicida up-regulated the mRNA expressions of isoforms 3 and 5, suggesting that these isoforms have roles in the innate immune system of kuruma shrimp.

Comparison of protein expression profiles of the hepatopancreas in Fenneropenaeus chinensis challenged with heat-inactivated Vibrio anguillarum and white spot syndrome virus

Fenneropenaeus chinensis (Chinese shrimp) culture industry, like other Penaeidae culture, has been seriously affected by the shrimp diseases caused by bacteria and virus. To better understand the mechanism of immune response of shrimp to different pathogens, proteome research approach was utilized in this study. Firstly, the soluble hepatopancreas protein samples in adult Chinese shrimp among control, heat-inactivated Vibrio-challenged and white spot syndrome virus-infected groups were separated by 2-DE (pH range, 4-7; sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and pH range, 3-10; tricine-SDS-PAGE). Then the differentially expressed protein spots (≥1.5-fold or ≤0.67-fold averagely of controls) were analyzed by LC-ESI-MS/MS. Using Mascot online database searching algorithm and SEQUEST searching program, 48 and 49 differentially expressed protein spots were successfully identified in response to Vibrio and white spot syndrome virus infection, respectively. Based on these results, we discussed the mechanism of immune response of the shrimp and shed light on the differences between immune response of shrimp toward Vibrio and white spot syndrome virus. This study also set a basis for further analyses of some key genes in immune response of Chinese shrimp.

Vaccination enhances early immune responses in white shrimp Litopenaeus vannamei after secondary exposure to Vibrio alginolyticus

BACKGROUND

Recent work suggested that the presence of specific memory or some form of adaptive immunity occurs in insects and shrimp. Hypervariable pattern recognition molecules, known as Down syndrome cell adhesion molecules, are able to mount specific recognition, and immune priming in invertebrates. In the present study, we attempted to understand the immune response pattern of white shrimp Litopenaeus vannamei which received primary (PE) and secondary exposure (SE) to Vibrio alginolyticus.

METHODOLOGY

Immune parameters and proliferation of haematopoietic tissues (HPTs) of shrimp which had received PE and SE to V. alginolyticus were measured. In the PE trial, the immune parameters and proliferation of HPTs of shrimp that received heat-killed V. alginolyticus (HVa) and formalin-inactivated V. alginolyticus (FVa) were measured. Mortality, immune parameters and proliferation of HPTs of 7-day-HVa-PE shrimp (shrimp that received primary exposure to HVa after 7 days) and 7-day-FVa-PE shrimp (shrimp that received primary exposure to FVa after 7 days) following SE to live V. alginolyticus (LVa) were measured. Phagocytic activity and clearance efficiency were examined for the 7∼35-day-HVa-PE and FVa-PE shrimp.

RESULTS

HVa-receiving shrimp showed an earlier increase in the immune response on day 1, whereas FVa-receiving shrimp showed a late increase in the immune response on day 5. The 7-day-FVa-PE shrimp showed enhancement of immunity when encountering SE to LVa, whereas 7-day-HVa-PE shrimp showed a minor enhancement in immunity. 7-day-FVa-PE shrimp showed higher proliferation and an HPT mitotic index. Both phagocytic activity and clearance maintained higher for both HVa-PE and FVa-PE shrimp after 28 days.

CONCLUSIONS

HVa- and FVa-receiving shrimp showed the bacteria agglutinated prior to being phagocytised. FVa functions as a vaccine, whereas HVa functions as an inducer and can be used as an immune adjuvant. A combined mixture of FVa and HVa can serve as a "vaccine component" to modulate the immunity of shrimp.

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.

Effect of probiotic Pediococcus acidilactici on antioxidant defences and oxidative stress of Litopenaeus stylirostris under Vibrio nigripulchritudo challenge

Antioxidant defences and induced oxidative stress tissue damage of the blue shrimp Litopenaeus stylirostris, under challenge with Vibrio nigripulchritudo, were investigated for a 72-h period. For this purpose, L. stylirostris were first infected by immersion with pathogenic V. nigripulchritudo strain SFn1 and then antioxidant defences: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (Gpx), Total antioxidant status (TAS), glutathiones and induced tissue damage (MDA and carbonyl proteins) were determined in the digestive gland at 0, 12, 24, 48 and 72 h post-infection (h.p.i.). In the meantime, TAS was also measured in the blood. Infection level of the shrimps during the challenge was followed by determining V. nigripulchritudo prevalence and load in the haemolymph of the shrimps. Changes in all these parameters during the 72-h.p.i. period were recorded for control shrimps and shrimps previously fed for one month with probiotic Pediococcus acidilactici MA18/5M at 10(7) CFU g(-1) of feed. Our results showed that immersion with V. nigripulchritudo led to maximal infection level in the haemolymph at 24 h.p.i. preceding the mortality peak recorded at 48 h.p.i. Significant decreases in the antioxidant defences were detected from 24 h.p.i. and beyond that time infection leaded to increases in oxidative stress level and tissue damage. Compared to control group, shrimps fed the probiotic diet showed lower infection (20% instead of 45% at 24 h.p.i. in the control group) and mortality (25% instead of 41.7% in the control group) levels. Moreover, infected shrimp fed the probiotic compared to uninfected control shrimps exhibited very similar antioxidant status and oxidative stress level. Compared to the infected control group, shrimps fed the probiotic sustained higher antioxidant defences and lower oxidative stress level. This study shows that bacterial infection leads to oxidative stress in L. stylirostris and highlighted a beneficial effect of P. acidilactici, suggesting both a competitive exclusion effect leading to a reduction of the infection level and/or an enhancement of the antioxidant status of the shrimps.

White shrimp Litopenaeus vannamei that received the hot-water extract of Gracilaria tenuistipitata showed earlier recovery in immunity after a Vibrio alginolyticus injection

White shrimp Litopenaeus vannamei which had been immersed in seawater containing the hot-water extract of Gracilaria tenuistipitata at 0 (control), 200, 400, and 600 mg L(-1) for 3 h, were challenged with Vibrio alginolyticus at 4.6 x 10(6) colony-forming units (CFU) shrimp(-1) and then placed in normal seawater (34 per thousand). The survival rates of shrimp immersed in 200, 400, and 600 mg L(-1) of the hot-water extract were significantly higher than those of control shrimp over 48-120 h. In another experiment, L. vannamei which had been immersed in the hot-water extract at 0, 200, 400, and 600 mg L(-1) for 3 h, were challenged with V. alginolyticus at 4.0 x 10(6) CFU shrimp(-1), and the immune parameters examined included the haemocyte count, phenoloxidase (PO) activity, respiratory burst (RB), and superoxide dismutase (SOD) activity at 12-120 h post-challenge after shrimp had been released into normal seawater. Shrimp not exposed to the hot-water extract or V. alginolyticus served as the background control. Results indicated that the haemocyte count, PO activity, RB, and SOD activity of shrimp immersed in 600 mg L(-1) were significantly higher than those of control shrimp at 12-72 h post-challenge. Results also indicated that total haemocyte count (THC), PO activity, RB and SOD activity of shrimp immersed in 400 and 600 mg L(-1) of the hot-water extract returned to the background values at 96, 48, 48, and 72 h, whereas these parameters of control shrimp returned to the original values at >120, >120, 96, and 96 h post-challenge, respectively. It was therefore concluded that L. vannamei that had been immersed in seawater containing the hot-water extract of G. tenuistipitata exhibited protection against V. alginolyticus as evidenced by the earlier recovery of immune parameters.