Phagocytic activity, respiratory burst, cytoplasmic free-Ca(2+) concentration and apoptotic cell ratio of haemocytes from the black tiger shrimp, Penaeus monodon under acute copper stress

Immunotoxicity and oxidative damage in Litopenaeus vannamei induced by polyethylene microplastics and copper co-exposure

This study examines the combined effects of polyethylene microplastics (PE-MP) and copper (Cu2+) on the immune and oxidative response of Litopenaeus vannamei. PE-MP adsorbed with Cu2+ at 2.3, 6.8, and 16.8 ng (g shrimp)-1) were injected into L. vannamei. Over 14 days, survival rates were monitored, and immune and oxidative stress parameters were assessed. The results showed that combined exposure to PE-MP and Cu2+ significantly reduced the survival rate and decreased total haemocyte count. Immune-related parameters (phagocytic rate, phenoloxidase and superoxide dismutase (SOD)) and antioxidant-related parameters (SOD, catalase and glutathione peroxidase mRNA and enzyme) also decreased, while respiratory burst activity significantly increased, indicating immune and antioxidant system disruption. Additionally, there was a significant increase in oxidative stress, as measured by malondialdehyde levels. Histopathological analysis revealed severe muscle, hepatopancreas, and gill damage. These results suggest that simultaneous exposure to PE-MP and Cu2+ poses greater health risks to white shrimp.

Immune-antioxidant trait, growth, splenic cytokines expression, apoptosis, and histopathological alterations of Oreochromis niloticus exposed to sub-lethal copper toxicity and fed thyme and/or basil essential oils enriched diets

Two experiments were conducted in this study, using 250 Oreochromis niloticus (O. niloticus) (average weight 30.28 ± 0.27 g). The first experiment was conducted to investigate the 96-h lethal concentration 50 (LC₅₀) of copper chloride (CuCl₂) using the probit analysis, seventy fish was divided into seven different concentration of CuCl₂ (0, 22, 23, 24, 25, 26, and 27 mg/L), the accurate Cu concentrations were (1.23, 5.36, 6.02, 6.98, 7.05, 7.93, 8.12 mg/L Cu). The second experiment was conducted for investigating the effect of dietary supplementation with thyme (Thymus vulgaris, T. vulgaris) and sweet basil (Ocimum basilicum, O. basilicum) essential oils (TEO and BEO respectively) against sub-lethal Cu exposure (1/10 96-h LC₅₀ of CuCl₂). About 180 fish was divided into six groups in triplicate (10 fish/replicate, 30 fish/group). Group 1 (C) was kept as a control group with no Cu exposure and was fed the control basal diet. Group 2 (C-Cu) was fed the control basal diet and simultaneously exposed to 1/10 of the 96 h LC₅₀ of CuCl₂ (2.574 mg/L) as a sub-lethal concentration of Cu, where the realistic Cu concentration was 3.976 mg/L. Group 3 (TEO) and group 4 (BEO) were fed the diets fortified with 1%TEO and BEO, respectively without exposure to Cu. Group 5 (TEO-Cu) and group 6 (BEO-Cu) were fed the diets fortified with 1%TEO and 1%BEO, respectively, and simultaneously exposed to 1/10 of the 96 h LC₅₀ of CuCl₂ (2.574 mg/L). The growth and behavioral performance, immunological response and its related gene expression, antioxidant status, stress biomarker indicators, apoptosis biomarkers, and histopathological alteration were investigated. The results of the first experiment showed that the 96-h LC₅₀ of CuCl₂ in O. niloticus was 25.740 mg/L with lower and upper confidence limits of 25.152 and 26.356 mg/L, respectively. The results of the second experiment showed that sub-lethal Cu exposure induced growth retardation (lowered final body weight, total weight gain, and specific growth rate %), behavioral abnormalities (slower swimming activity and feeding performance), immunosuppression (lowered nitric oxide, complement-3, lysozyme, total proteins, albumin, and globulin), and lowering the hepatic antioxidant functions (higher MDA, and lower SOD, CAT, and GPx) in the exposed fish. Furthermore, alteration in the immune-related genes expression (down-regulation of IL-10 and TGF-β and up-regulation of IL-1β, IL-6, IL-8, and TRL-4), hepato-renal dysfunction (elevated ALT, AST, urea, and creatinine), and high levels of serum stress indicators (cortisol and glucose) were markedly evident. sub-lethal Cu toxicity induced significant up-regulation of apoptosis biomarkers involving, nuclear factor-κβ (NF-κβ), Bcl-2 Associated X-protein (BAX), meanwhile, the expression of B-cell lymphoma 2 (BCL2) and Proliferating cell nuclear antigen (PCNA) was remarkably down-regulated. In addition, apoptosis was also evident by histopathological investigation of branchial, hepatic, and renal sections. TEO and/or BEO dietary supplementation mitigate the destructive impacts of sub-lethal Cu exposure in O. niloticus, depending on the results of our study, it could be concluded that TEO and BEO with a 1% dietary level could be a promising antioxidant, immunostimulant, anti-stress factors, and anti-apoptosis mediators against heavy metal contaminants (Cu) in O. niloticus, providing a solution to the problem of aquatic bodies pollution, consequently aiding in the development of aquaculture industry.

Response of microbiota and immune function to different hypotonic stress levels in giant freshwater prawn Macrobrachium rosenbergii post-larvae

This study explored the effects of different hypotonic stress levels on antioxidant capacity, microbial composition, and gene expression of Macrobrachium rosenbergii post-larvae. The salinity of the control group was 15 ‰ (S15), and the hypotonic stress groups included three levels of 10 ‰ (S10), 8 ‰ (S8), and 6 ‰ (S6). Different hypotonic stress levels caused oxidative damage in post-larvae, evidenced by decreased superoxide dismutase (SOD) and anti-superoxide anion free radical (ASAFR). They increased malondialdehyde (MDA), nitric oxide (NO), and inducible nitric oxide synthase (iNOS) levels. Microbiological analysis exhibited that different hypotonic stress levels significantly changed microbial composition and diversity. The microbial composition in the water environment where post-larvae living was different from post-larvae. The pathogenic bacteria, including Vibrio and Flavobacterium, were abundant in S6. Transcriptome analysis showed 2, 7967, 297 DEGs, including 1, 3564, 27 up-regulated genes and 1, 4403, 270 down-regulated genes in S10, S8, and S6 groups, respectively. KEGG enrichment results showed that immune and glucose metabolism-related pathways were enriched significantly. Correlation network analysis demonstrated close interactions among antioxidant parameters, microbes, and differentially-expressed genes. In conclusion, hypotonic stress reduced the antioxidant capacity, caused oxidative damage, and altered microbial composition in M. rosenbergii post-larvae. Moreover, when the salinity is below 8 ‰, hypotonic stress impairs the immune system of M. rosenbergii post-larvae.

Bioaccumulation of arsenic and immunotoxic effect in white shrimp (Penaeus vannamei) exposed to trivalent arsenic

Trivalent arsenic (As (III)) contamination in the marine environment can produce adverse effects in crustaceans. The present study investigated the chronic toxicity of As (III) in white shrimp (Penaeus vannamei) by analyzing the tissue bioaccumulation and non-specific immune responses. Shrimps were exposed to 0 (control), 50, 500, and 2500 μg/L of As (III) for 21 days. The results showed that the hepatopancreas was the main tissue of arsenic accumulation in white shrimp. The cumulative concentration of total arsenic and inorganic arsenic but not arsenobetaine was positively correlated with the exposure concentration. In vitro As (III) treatment (0-2500 μg/L) with haemocytes isolated from healthy shrimp did not cause the cytotoxicity, but this arsenic treatments inhibited the phagocytic rate and O₂^- production. Moreover, the decrease of total haemocyte count and the inhibition of phagocytic rate, phagocytic index, O₂^- production and phenoloxidase activity were observed in white shrimp under the exposure of As (III) over a period of 21 days. This study revealed that chronic As (III) stress could disturb arsenic metabolism and immune responses in P. vannamei.

Effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense

As a non-essential and toxic element, cadmium poses an important threat to aquatic organisms and human food safety. In this study, the effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense were studied from the physiological and biochemical indexes, histology and expression of related genes. These results showed that low concentrations (0.01, 0.02 mg/L) of cadmium have a positive effect on the non-specific immunity of M. nipponense, but high concentration (0.04 mg/L) of cadmium could inhibit or even damage the non-specific immunity of M. nipponense. The cadmium could induce oxidative stress in M. nipponense, and M. nipponense actived the antioxidant defense system to deal with oxidative stress, but high concentration (0.04 mg/L) of cadmium could inhibit the antioxidant defense system of M. nipponense, leading to oxidative damage, and may induce apoptosis in severe case. At the same time, the results of histology showed that cadmium can damage the structure of gill and hepatopancreas tissues of M. nipponense. This study provides theoretical data for evaluating the influences of heavy metal cadmium on M. nipponense and the toxic mechanism of heavy metal cadmium.

Phycoerythrin from Colaconema sp. Has Immunostimulatory Effects on the Whiteleg Shrimp Litopenaeus vannamei and Increases Resistance to Vibrio parahaemolyticus and White Spot Syndrome Virus

Simple Summary

In this study, we found that phycoerythrin from Colaconema sp. can differentially stimulate the immune response of whiteleg shrimp in vitro and in vivo and could potentially be used as an immunomodulator in shrimp culture.

Abstract

We investigated whether phycoerythrin (PE), a pigment sourced from marine algae, could act as an immunomodulatory agent in whiteleg shrimp (Litopenaeus vannamei). To this end, PE was extracted and purified from a PE-rich macroalgae, Colaconema sp. Our in vitro analysis demonstrated that PE enhanced prophenoloxidase and phagocytosis activity but inhibited the production of reactive oxygen species in hemocytes. Additionally, the PE signal could be detected using an in vivo imaging system after its injection into the ventral sinus of the cephalothorax of whiteleg shrimp. The expression profiles of fourteen immune-related genes were monitored in hemocytes from whiteleg shrimp injected with 0.30 μg of PE per gram of body weight, and crustin, lysozyme, penaiedin 4, and anti-lipopolysaccharide factor showed up-regulated post-stimulation. The induction of immune genes and enhancement of innate immune parameters by PE may explain the higher survival rates for shrimp that received different doses of PE prior to being challenged with Vibrio parahaemolyticus or white spot syndrome virus compared to controls. Combined, these results show that PE from Colaconema sp. can differentially stimulate the immune response of whiteleg shrimp in vitro and in vivo and could potentially be used as an immunomodulator in shrimp culture.

Gender Differences in Hemocyte Immune Parameters of Hong Kong Oyster Crassostrea hongkongensis During Immune Stress

Gender differences in individual immune responses to external stimuli have been elucidated in many invertebrates. However, it is unclear if gender differences do exist in the Hong Kong oyster Crassostrea hongkongensis, one of the most valuable marine species cultivated along the coast of South China. To clarify this, we stimulated post-spawning adult C. hongkongensis with Vibrio harveyi and lipopolysaccharide (LPS). Gender-based differences in some essential functional parameters of hemocytes were studied via flow cytometry. Obvious gender-, subpopulation-, and immune-specific alterations were found in the hemocyte immune parameters of C. hongkongensis. Three hemocyte subpopulations were identified: granulocytes, semi-granulocytes, and agranulocytes. Granulocytes, the chief phagocytes and major producers of esterase, reactive oxygen species, and nitric oxide, were the main immunocompetent hemocytes. Immune parameter alterations were notable in the accumulation of granulocyte esterase activities, lysosomal masses, nitric oxide levels, and granulocyte numbers in male oysters. These results suggest that post-spawning-phase male oysters possess a more powerful immune response than females. Gender and subpopulation differences in bivalve immune parameters should be considered in the future analysis of immune parameters when studying the impact of pathogenic or environmental factors.

DNA damage, immunotoxicity, and neurotoxicity induced by deltamethrin on the freshwater crayfish, Procambarus clarkii

Pyrethroid pesticides are applied to both agricultural and aquacultural industries for pest control. However, information of their impact on the commercial important freshwater crayfish, Procambarus clarkii is scarce. Therefore, the present study aimed to characterize to effects of a commonly used pyrethroid pesticide, deltamethrin on DNA damage, immune response, and neurotoxicity in P. clarkii. Animals were exposed to 7, 14, and 28 ng/L of deltamethrin, which correspond to 1/8, 1/4, and 1/2 of the LC50 (96 hours) of this pyrethroid to P. clarkii. Significant increase of olive tail moment (OTM) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) was found after deltamethrin exposure in a dose-dependent way. Total hemocyte counts (THC) and activities of immune-related enzymes including acid phosphatase (ACP), lysozyme (LZM), and phenoloxidase (PO) were all decreased and significantly lower than control at concentration of 28 ng/L after 96 hours exposure. Acetylcholinesterase (AChE) activity, an indicator of neurotoxic effect was investigated and it was decreased significantly in muscles at 14 and 28 ng/L after 24 hours exposure. The level of intracellular reactive oxygen species (ROS) in hemocytes was also measured and the significant increase of ROS was found at 14 and 28 ng/L concentrations. The results revealed that deltamethrin induced DNA damage, immunotoxicity, and neurotoxicity in P. clarkii by excessive generation of ROS. Because of the dose-dependent responses of all parameters under exposure of deltamethrin at environmentally realistic concentrations, these parameters could be used as sensitive biomarkers for risk assessment of deltamethrin in aquaculture area.

Effects of Vibrio parahaemolyticus infection on physiological response, histopathology and transcriptome changes in the mud crab (Scylla paramamosain)

Mud crab (Scylla paramamosain) is an important economic species in China. Vibrio parahaemolyticus infection have caused a great economic loss in mud crab farming. The mechanism involved in the immune responses of mud crab to V. parahaemolyticus is unclear. In this study, the physiological and immune response to V. parahaemolyticus infection were investigated in S. paramamosain. The results showed that V. parahaemolyticus infection decreased total hemocyte counts, led to cytological damage, and caused high mortality. Transcriptome analysis showed that 1327 differentially expressed genes (DEGs), including 809 up-regulated and 518 down-regulated ones, were obtained after V. parahaemolyticus challenge. These DEGs were mainly involved in the immune response and infectious disease. Additionally, transcriptome analysis revealed that Toll, immune deficiency (IMD), and prophenoloxidase signalling pathways played essential roles in antibacterial immunity against V. parahaemolyticus infection in mud crab.

Oxidative and apoptotic effects of fluoxetine and its metabolite norfluoxetine in Daphnia magna

The aim of this study was to investigate the oxidative and apoptotic potential of fluoxetine, a widely used antidepressant in Turkey and the world, and of its metabolite norfluoxetine on a model non-target organism, Daphnia magna to see how exposure to this group of antidepressants (specific serotonin reuptake inhibitors) could affect the aquatic environment in which they end up. Juvenile D. magna specimens were chronically exposed to fluoxetine and norfluoxetine alone and in combination at concentrations found in the aquatic environment (0.091 and 0.011 μg/L, respectively) and to their 10-fold environmental concentrations for 21 days. Another group of 17-day-old animals were subacutely exposed to 100-fold environmental concentrations for four days. After exposure, we measured their glutathione peroxidase (GPx) and cholinesterase (ChE) activities, thiobarbituric acid-reactive substances (TBARS), and total protein content spectrophotometrically, while mitochondrial membrane potential (MMP) was analysed by fluorescence staining, and cytochrome c and ERK1/2 protein content by Western blotting. This is the first-time cytochrome c and ERK1/2 were determined at the protein level in D. magna. We also measured their carapace length, width, and caudal spine length microscopically. At environmental concentrations fluoxetine and norfluoxetine caused an increase in ChE activity and brood production. They also caused a decrease in juvenile carapace length, width, and caudal spine length and depolarised the mitochondrial membrane. At 10-fold environmental concentrations, GPx activity, lipid peroxidation levels, cytochrome c, and ERK1/2 protein levels rose. The most pronounced effect was observed in D. magna exposed to norfluoxetine. Norfluoxetine also decreased brood production. Similar effects were observed with subacute exposure to 100-fold environmental concentrations. However, total protein content decreased. All this confirms that fluoxetine and norfluoxetine have oxidative and apoptotic potential in D. magna. Daphnia spp. have a great potential to give us precious insight into the mechanisms of environmental toxicants, but there is still a long way to go before they are clarified in these organisms.

Effects of dietary monocalcium phosphate supplementation on the anti-oxidative capacity, anti-bacteria function in immune organs of obscure puffer (Takifugu obscurus) after infection with Aeromonas hydrophila

The purpose of the present study was to explore the impaired anti-bacteria ability in immune organs and immune systems of obscure puffer induced by chronic dietary phosphorus (P) deficiency. Fish were fed diets supplemented with 6 g/kg P (P6) and 0 g/kg P (P0) respectively for 15 weeks, and lower final body weight, feed intake, weight gain, whole body P content and bone P content were observed in fish fed P0 diet (P < 0.05). Then the fish were continued to feed for 3 weeks and intraperitoneal injection with PBS (P6+PBS) and Aeromonas hydrophila (A.hydrophila) (P6 + A.hydrophila and P0 + A.hydrophila), and sampled at 3, 6, 12 and 24 h. The results showed that dietary P deficiency lowered survival rate, total hemocyte count, whereas enhanced ROS production and apoptosis rate of obscure puffer compared to the 6 g/kg P supplemented group after infection. Moreover, compared to the P sufficient group, puffer fish fed P deficient diet decreased the expressions of antioxidant genes catalase (cat) and glutathione reductase (gr), immune-related genes toll-like receptor 2 (tlr-2) and anti-inflammatory factors transforming growth factor β1 (tgf-β1) and interleukin 11 (il-11) while increased pro-inflammatory cytokines tumor necrosis factor α (tnf-α), interleukin 1β (il-1β) and interleukin 8 (il-8) in head kidney post-infection. In addition, dietary P deficiency decreased the hepatic gene expressions of anti-apoptotic factor B-cell lymphoma 2 (bcl-2) and bax-inhibitor 1 (bi-1), accompanied by increasing the mRNA expressions of pro-apoptotic factor caspase 3, caspase 8 and caspase 9 compared to the P sufficient group after A.hydrophila infection. In conclusion, dietary P deficiency impaired the anti-bacteria function of the immune system as well as immune organs by increasing oxidative stress and aggravating the inflammatory response and apoptosis in obscure puffer under the A.hydrophila challenge.

Immune response to abamectin-induced oxidative stress in Chinese mitten crab, Eriocheir sinensis

It is known that abamectin (ABM) inflicts oxidative damage on aquatic animals; however, knowledge about the immune response under pesticide-induced oxidative stress is incomplete. In the present study, several cellular and humoral immune parameters, including total haemocyte counts (THC), lysosomal membrane stability (LMS), activities of acid phosphatase (ACP), alkaline phosphatase (AKP) and lysozyme (LZM) were investigated to reveal the effects of ABM exposure on the immune defence mechanisms of the important freshwater crab, Erocheir sinensis. According to the results, a significant increase of THC was found in low concentration groups (0.03 and 0.06 mg/L), while dramatic decreases occurred in high concentration groups (0.12 and 0.24 mg/L) after 96 h of exposure. We also detected significant increases of reactive oxygen species (ROS) in haemocytes at 0.12 and 0.24 mg/L, and there was a dose- and time-dependent decrease of lysosomal membrane stability. These results suggest that the excessive generation of ROS induced by ABM may be leading the massive collapse of lysosomal membrane, which in turn may be causing the sharp drop of haemocyte counts in E. sinensis. The increase of hydrolytic enzymes ACP and AKP at low concentrations and the decrease at high concentrations also indicate an immune response associated with haemocytes status under stress. However, activities of LZM decreased significantly. After injection of Aeromonas hydrophil, mortalities increased under exposure to ABM and were positively related to ABM concentration. These results confirm that ABM exposure has the ability to impair immune defence and result in the host's susceptibility to pathogens.

Avermectin induces the oxidative stress, genotoxicity, and immunological responses in the Chinese Mitten Crab, Eriocheir sinensis

Avermectin is commonly used in aquaculture systems for pest control in recent decades in China. However, no information is provided for the toxic effect to the important commercial species, Chinese mitten crab, Eriocheir sinensis. To investigate the aquatic toxicity of avermectin, an acute toxic test was performed in this study. The results showed that the 48 h- and 96 h- LC₅₀ were 1.663 and 0.954 mg/L, respectively. For further research, crabs were exposed to sublethal concentrations of 0.03, 0.06, 0.12, 0.24 and 0.48 mg/L. Levels of antioxidants, including superoxide dismutase (SOD), catalase (CAT) and total antioxidant capacity (T-AOC) were significantly (P<0.05) decreased with dose- and time- dependent responses, meanwhile the oxidative products including malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and protein carbonyl in serum increased significantly (P<0.05) at concentrations of 0.24 and 0.48 mg/L throughout the experiment. A significant (P<0.05) increase of intracellular ROS and decrease of phagocytic activity was observed in high concentration groups, with dose- and time- dependent manners during the exposure. In addition, serious genetic damage was detected, for the significant increase (P<0.05) of both comet ratio and %DNA in tail at each concentration, and micronucleus (MN) frequency at concentrations of 0.12, 0.24 and 0.48 mg/L at 96 h. These results indicated that sublethal concentration exposure of avermectin had a prominent toxic effect on E. sinensis based on the oxidative stress induced by generated ROS, immunological activity inhibition and genotoxicity.

The key differentially expressed genes and proteins related to immune response in the spleen of pufferfish (Takifugu obscurus) infected by Aeromonas hydrophila

The immune mechanism elicited in pufferfish (Takifugu obscurus) against the invasion of Aeromonas hydrophila is still poorly understood. We examined the spleen of pufferfish at the transcriptome and proteome levels by using Illumina-seq and TMT coupled mass spectrometry after 12 h infection by A. hydrophila, respectively. A total of 2,339 genes (1,512 up-regulated and 827 down-regulated) and 537 (237 up-regulated and 300 down-regulated) proteins were identified. GO and KEGG analyses revealed that the responses to stimulus were the main biological processes, intestinal immune network for IgT production and calcium signaling pathway. Fourteen genes (8 up-regulated and 6 down-regulated) and proteins (5 up-regulated and 9 down-regulated) involved immune responses or signal transduction were validated by qRT-PCR and parallel reaction monitoring to confirm the reliability of the transcriptomic and proteomic analyses, respectively. Moreover, qRT-PCR and flow cytometry were used to detect dynamics of the genes in calcium signaling pathway and changes of concentration of cytoplasm Ca²⁺ in spleen cells within a 72 h challenge. This study provides the findings regarding immune response, especially intestinal immune network for IgT production pathway and calcium signaling pathway at the molecular, protein and cellular in pufferfish after infection by A. hydrophila. These results would provide a new insight and molecular targets into the response to pathogenic infection in pufferfish.

Identification and characterization of differentially expressed genes in hepatopancreas of oriental river prawn Macrobrachium nipponense under nitrite stress

The oriental river prawn Macrobrachium nipponense is a highly adaptable, tolerant, and fecund freshwater prawn that inhabits a wide range of aquatic environments. The hepatopancreas of crustaceans is not only a site for secretion of digestive enzymes, and also plays important roles in several metabolic processes, such as lipid and carbohydrate metabolism. It is the main organ for the detoxification and immunity. In this study, high-throughput sequencing techniques were used to detect the effect of nitrite stress (10 mg/L nitrite-N for 48 h) on gene expression in the hepatopancreas of M. nipponense. A total of 13,769 million reads were harvested, and 94,534 transcripts were de novo assembled using Trinity software and produced 56,054 non-redundant transcripts. A total of 825 differentially expressed genes were obtained comparing 48 h nitrite stress with control group. In the analysis of GO and KEGG database, significant differences were found in 49 pathways. Immune-related pathways under nitrite stress included arginine and proline metabolism, glutamate metabolism, Jak-Stat signaling pathway, endocytosis, wnt signaling pathway, RIG-I-like receptor signaling pathway, TGF-beta signaling pathway, GnRH signaling pathway and phagosome. Apoptosis-related pathway was also significantly altered, such as lysosome and apoptosis. Remarkably, nitrite stress altered the expression patterns of key apoptosis genes (tetraspanins-like protein, LAMP, CD63, caspase 3C and Caspase 1) and immune genes (Serine proteinase-like protein, C-type lectin, daf-36, SOCS-2, alpha-2-macroglobulin), confirmed that nitrite-stress induce immune response and eventually even apoptosis. This study provided a new insight into the role of hepatopancreas in crustaceans, and further investigation will continue.

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

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

Effects of Copper on Hemocyte Apoptosis, ROS Production, and Gene Expression in White Shrimp Litopenaeus vannamei

Copper, a common chemical contaminant in aquatic environment, is known to be toxic to aquatic life at high concentrations. In the present study, we evaluated the apoptotic cell ratio and ROS production in hemocytes of the white shrimp Litopenaeus vannamei exposed to 1 or 5 mg L^-1 Cu for 0, 3, 6, 12, 24, and 48 h. The expression changes of antioxidant biomarker genes, i.e., copper-zinc superoxide dismutase (Cu-Zn SOD) and catalase (CAT), apoptosis-related genes, i.e., caspase-3 and inhibitor of apoptosis protein (IAP), and a specific biomarker gene of heavy metal pollution, i.e., metallothionein (MT), were also determined in hemocytes. Significant increases in ROS production were observed in both treatment groups at each time points. The apoptotic cell ratios were significantly increased at 6-48 h among shrimp exposed to 1 mg L^-1 Cu and at each time points in 5 mg L^-1 Cu group. These results indicated that Cu would induce oxidative stress and apoptosis in the hemocyte of L. vannamei. Quantitative real-time PCR analysis revealed that the relative expression levels of Cu-Zn SOD, CAT, caspase-3, IAP, and MT were upregulated in a dose-dependent and time-dependent manner, suggesting the involvement of these genes in stress response against Cu exposure.

Molecular characterization and function of the Prohibitin2 gene in Litopenaeus vannamei responses to Vibrio alginolyticus

Prohibitin2 (PHB2), a potential tumor suppressor protein, plays important roles in inhibition of cell cycle progression, transcriptional regulation, apoptosis and the mitochondrial respiratory chain. To explore its potential roles in crustaceans' immune responses we have identified and characterized LvPHB2, a 891 bp gene encoding a 297 amino acids protein in the shrimp Litopenaeus vannamei. Expression analyses showed that LvPHB2 is expressed in all examined tissues, and largely present in cytoplasm, correlating with its known anti-oxidation function in mitochondria. Luciferase reporter assays showed that over-expression of LvPHB2 could activate the p53 pathway, indicating that it might participate in apoptosis regulation. Quantitative real-time PCR revealed that infection with Vibrio alginolyticus induces its up-regulation in hepatopancreas. Moreover, RNAi knock-down of LvPHB2 in vivo raises mortality rates of L. vannamei infected by V. alginolyticus, and affects expression of STAT3, Caspase3 and p53 genes. We found significantly higher reactive oxygen species production, DNA damage and apoptosis rates in LvPHB2-silenced shrimp challenged with V. alginolyticus than in controls injected with a Green Fluorescent Protein-silencing construct. Our results suggest that LvPHB2 plays a vital role in shrimp responses to V. alginolyticus infection through its participation in regulation of oxidants and apoptosis.

Beta 1,3/1,6-glucan and vitamin C immunostimulate the non-specific immune response of white shrimp (Litopenaeus vannamei)

This study mainly evaluated the effects of orally administered beta 1,3/1,6-glucan and vitamin C on the nonspecific immune responses of white shrimp (Litopenaeus vannamei). In this study, we found that the white shrimp oral administration with 1 g/kg of beta 1,3/1,6-glucan effectively enhanced O2(-) production and phenoloxidase and superoxide dismutase activity. Shrimp were oral administration with 0.2 g/kg of vitamin C presented beneficial nonspecific immune responses and enzyme activity and also observed in the beta 1,3/1,6-glucan treatment groups. Consequently, we compared the alterations in the immune activity between the beta 1,3/1,6-glucan and vitamin C groups and the evidence illustrated that combination of beta 1,3/1,6-glucan and vitamin C presented an additive effect on inducing the nonspecific immune responses of white shrimp.

Effect of lipopolysaccharide on the hemocyte apoptosis of Eriocheir sinensis

In the present study, we investigated the possible toxicity mechanism of lipopolysaccharide (LPS) extracted from Gram-negative bacteria in Eriocheir sinensis hemocytes. Apoptotic hemocytes and reactive oxygen species (ROS) production induced by the LPS were monitored by the combination of flow cytometry and microscope observation. It was shown that LPS induced serious damage on the DNA and morphological changes in hemocytes, including cell shrinkage, fracture of nucleus membrane, margination, condensation and fragmentation of chromatin, and formation of apoptotic bodies indicating obvious hemocyte apoptosis. As compared with the control group, the apoptotic cell ratio increased to 30.61% and 39.01% after 1-h exposure and 57.72% and 75.01% after 2-h exposure to 1 and 10 μg/ml LPS, respectively (P<0.05). Significant outburst of ROS production was observed in LPS-treated hemocytes with approximately 176.6% of relative dichlorofluorescein mean fluorescence at 1-h exposure, followed by a drastic decline (P<0.05). These results indicated that LPS would induce oxidative stress on hemocytes from E. sinensis and cause ROS burst, DNA damage, and subsequently apoptosis. The process of ROS-mediated apoptosis might be one of the potential toxicity mechanisms of LPS on crustacean hemocytes.

Immune-associated parameters and antioxidative responses to cadmium in the freshwater crab Sinopotamon henanense

Cadmium (Cd) is a toxic heavy metal pollutant and is known to exert adverse effects in organisms. In this study, we examined immune-related and antioxidative parameters in crabs exposed to sublethal levels of Cd. The results showed that Cd exposure elicited a significant accumulation in hemolymph, a decrease in total hemocyte counts, and the production of reactive oxygen species (ROS). Cd treatment also upregulated activities of antioxidant enzymes including superoxide dismutase, catalase, and glutathione peroxidase in the hemocytes of crabs. Treatment with Cd further decreased the stability of lysosomal membranes in hemocytes and induced substantial changes of immune-related parameters including acid phosphatase and alkaline phosphatase. However, the activity of lysozyme varied weakly throughout the Cd treatment period. Our results suggest that Cd exposure caused immunomodulation, a potentially harmful immunity function and damage in the antioxidant system of Sinopotamon henanense.

Copper-induced oxidative damage to the prophenoloxidase-activating system in the freshwater crayfish Procambarus clarkii

Previous studies have demonstrated copper-induced proteins damage in gill and hepatopancreas of the freshwater crayfish Procambarus clarkii, but little information is available about its effects on key component of the innate defense in haemolymph. In the present study, we evaluated the relationship between oxidative carbonylation and prophenoloxidase-activating system (proPO-AS) activity, by exposing P. clarkii to sub-lethal concentrations (1/50, 1/12, 1/6 and 1/3 of the 96 h LC50) Cu(2+) up to 96 h. Six biomarkers of oxidative stress, i.e. reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), protein carbonyl (PC), malondialdehyde (MDA) and DNA-protein crosslinks (DPCs), and six indicators of immune status, i.e. total hemocyte counts (THCs), differential hemocyte counts (DHCs), hemocyanin (HC), prophenoloxidase (proPO), serine protease (SP) and phenoloxidase (PO), were determined in haemolymph. The results indicated that there was a significant increase (P < 0.05) in the levels of ROS, PC, MDA and DPCs accompanied by markedly decreased (P < 0.05) activities of proPO, SP, PO and HC in a dose and time dependent manner. The significant and positive correlations (P < 0.01) between ROS production and the formation of PC, MDA and DPCs were observed in crayfish at 96 h. There was a significant negative correlation (P < 0.01) between the levels of protein carbonyls and the activities of proPO and SP in hemocyte lysate supernatant and PO and HC in haemolymph. Carbonylated proteins may be recognized not merely as a specific signal in oxidative stress pathways but also as a "non-self" molecule in proPO-AS. In crayfish species, copper-catalyzed protein carbonylation may be one of the main mechanisms for immunity dysfunction in proPO-AS.

Induction of apoptosis by UV in the flat oyster, Ostrea edulis

Apoptosis is a fundamental feature in the development of many organisms and tissue systems. It is also a mechanism of host defense against environmental stress factors or pathogens by contributing to the elimination of infected cells. Hemocytes play a key role in defense mechanisms in invertebrates and previous studies have shown that physical or chemical stress can increase apoptosis in hemocytes in mollusks. However this phenomenon has rarely been investigated in bivalves especially in the flat oyster Ostrea edulis. The apoptotic response of hemocytes from flat oysters, O. edulis, was investigated after exposure to UV and dexamethasone, two agents known to induce apoptosis in vertebrates. Flow cytometry and microscopy were combined to demonstrate that apoptosis occurs in flat oyster hemocytes. Investigated parameters like intracytoplasmic calcium activity, mitochondrial membrane potential and phosphatidyl-serine externalization were significantly modulated in cells exposed to UV whereas dexamethasone only induced an increase of DNA fragmentation. Morphological changes were also observed on UV-treated cells using fluorescence microscopy and transmission electron microscopy. Our results confirm the apoptotic effect of UV on hemocytes of O. edulis and suggest that apoptosis is an important mechanism developed by the flat oyster against stress factors.

A Rac1 GTPase is a critical factor in the immune response of shrimp (Litopenaeus vannamei) to Vibrio alginolyticus infection

The small GTPase Rac1 acts as a molecular switch for signal transduction that regulates various cellular functions. However, its functions in crustaceans remain unclear. In this study, a cDNA encoding a RAS GTPase (LvRac1) in the Pacific white shrimp (L. vannamei) was identified and characterized. A recombinant variant of this GTPase, rLvRac1, was expressed in the model organism P. pastoris and its expression was confirmed by mass spectrometry. Biochemical assays indicated that the recombinant protein retained GTPase activity and was expressed in all of the organism's tested tissues. Injection of the bacterium V. alginolyticus into L. vannamei induced hepatopancreatic upregulation of LvRac1 expression. Moreover, knocking down LvRac1 in vivo significantly reduced the expression of the L. vannamei p53 and Cu/Zn superoxide dismutase genes (Lvp53 and LvCu/Zn SOD, respectively) while increasing that of the galectin gene (Lvgal). Hemolymph samples from control and LvRac1-silenced L. vannamei individuals were analyzed by flow cytometry, revealing that the latter exhibited significantly reduced respiratory burst activity and total hemocyte counts. Cumulative mortality in shrimp lacking LvRac1 was significantly greater than in control groups following V. alginolyticus challenge. The silencing of LvRac1 by double-stranded RNA injection thus increased the V. alginolyticus challenge sensitivity of L. vannamei and weakened its bacterial clearance ability in vivo. Suppressing LvRac1 also promoted the upregulation of Lvp53, LvCu/ZnSOD, and Lvgal following V. alginolyticus injection. Taken together, these results suggest that LvRac1 is important in the innate immune response of shrimp to V. alginolyticus infection.

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.

Distinct role of Hsp70 in Drosophila hemocytes during severe hypoxia

Severe hypoxia can lead to injury and mortality in vertebrate or invertebrate organisms. Our research is focused on understanding the molecular mechanisms that lead to injury or adaptation to hypoxic stress using Drosophila as a model system. In this study, we employed the UAS-Gal4 system to dissect the protective role of Hsp70 in specific tissues in vivo under severe hypoxia. In contrast to overexpression in tissues such as muscles, heart, and brain, we found that overexpression of Hsp70 in hemocytes of flies provides a remarkable survival benefit to flies exposed to severe hypoxia for days. Furthermore, these flies were tolerant not only to severe hypoxia but also to other stresses such as oxidant stress (e.g., paraquat feeding or hyperoxia). Interestingly we observed that the better survival with Hsp70 overexpression in hemocytes under hypoxia or oxidant stress is causally linked to reactive oxygen species (ROS) reduction in whole flies. We also show that hemocytes are a major source of ROS generation, leading to injury during hypoxia, and their elimination results in a better survival under hypoxia. Hence, our study identified a protective role for Hsp70 in Drosophila hemocytes, which is linked to ROS reduction in the whole flies and thus helps in their remarkable survival during oxidant or hypoxic stress.