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

Immune regulation mediated by JAK/STAT signaling pathway in hemocytes of Pacific white shrimps, Litopenaeus vannamei stimulated by lipopolysaccharide

To understand the regulatory mechanism of Janus kinase/Signal Transducers and Activators of Transcription (JAK/STAT) signaling pathway on the immune system of the Pacific white shrimp, Litopenaeus vannamei, RNA interference technique was used to investigate the effects of JAK/STAT signaling pathway on the immune response of hemocyte in Litopenaeus vannamei stimulated by lipopolysaccharide (LPS). The results showed that 1) after 6 h of LPS stimulation, the expression levels of immune genes in hemocyte were significantly up-regulated (P < 0.05), the immune defense ability (hemocyte number, phagocytosis rate, hemagglutination activity, bacteriolytic activity, antibacterial activity, prophenoloxidase system activity) and the hemocyte antioxidant ability were significantly higher than the control group, especially at 12 h. 2) After 48 h of STAT gene interference, the expression levels of immune genes in hemocytes were significantly down-regulated, and the immune defense ability (hemocyte count, phagocytosis rate, plasma agglutination activity, lysozyme activity, antibacterial activity, proPO system activity) and the antioxidant ability were reduced and significantly lower than control. Concurrently, after LPS stimulation, the immune indexes were significantly up-regulated at 12 h to the maximum but was still lower the undisturbed LPS group. These results indicate that JAK/STAT signaling pathway is involved in the immune regulation mechanism of L. vannamei against LPS stimulation through positive regulation of cellular immune and humoral immune. These results provide a basis for further research on the role and status of JAK/STAT signaling pathway in the immune defense of crustaceans.

Comparative transcriptomics reveals the immune dynamics during the molting cycle of swimming crab Portunus trituberculatus

Molting is one of the most important biological processes of crustacean species, and a number of molecular mechanisms facilitate this complex procedure. However, the understanding of the immune mechanisms underlying crustacean molting cycle remains very limited. This study performed transcriptome sequencing in hemolymph and hepatopancreas of the swimming crab (Portunus trituberculatus) during the four molting stages: post-molt (AB), inter-molt (C), pre-molt (D), and ecdysis (E). The results showed that there were 78,572 unigenes that were obtained in the hemolymph and hepatopancreas of P. trituberculatus. Further analysis showed that 98 DEGs were involved in immunity response of hemolymph and hepatopancreas, and most of the DEGs participated in the process of signal transduction, pattern recognition proteins/receptors, and antioxidative enzymes system. Specifically, the key genes and pathway involved in signal transduction including the GPCR126, beta-integrin, integrin, three genes in mitogen-activated protein kinase (MAPK) signaling cascade (MAPKKK10, MAPKK4, and p38 MAPK), and four genes in Toll pathway (Toll-like receptor, cactus, pelle-like kinase, and NFIL3). For the pattern recognition proteins/receptors, the lowest expression level of 11 genes was found in the E stage, including C-type lectin receptor, C-type lectin domain family 6 member A and SRB3/C in the hemolymph, and hepatopancreatic lectin 4, C-type lectin, SRB, Down syndrome cell adhesion molecule homolog, Down syndrome cell adhesion molecule isoform, and A2M. Moreover, the expression level of copper/zinc superoxide dismutase isoform 4, glutathione peroxidase, glutathione S-transferase, peroxiredoxin, peroxiredoxin 6, and dual oxidase 2 in stage C or stage D significantly higher than that of stage E or stage AB. These results fill in the gap of the continuous transcriptional changes that are evident during the molting cycle of crab and further provided valuable information for elucidating the molecular mechanisms of immune regulation during the molting cycle of crab.

Structural and functional diversity of lectins associated with immunity in the marine shrimp Litopenaeusvannamei

Lectins are important pattern recognition receptors (PRRs) and their immunological action is related to the recognition of glycans present in the pathogen cells surface. The lectins described for Litopenaeus vannamei are divided into C-type, L-type and galectin, which are mainly expressed in hepatopancreas and hemocytes. They are involved in several immune response pathways, such as phagocytosis, hemocytes recruitment, prophenoloxidase activation, and gene regulation. Although lectins have multiple immune functions, most experimental challenges focus only on WSSV and Vibrio sp. This article is a detailed review on the role of lectins in L. vannamei immune system, bringing together information on molecular structure, temporal and special expression and immune function, highlighting the wide participation of these molecules in shrimp innate immune system.

Effects of ammonia-N stress on molecular mechanisms associated with immune behavior changes in the haemocytes of Litopenaeus vannamei

High concentration of ammonia-N will inhibit the immune defense of aquatic animals. The neuroendocrine-immune (NEI) regulatory mechanism under ammonia-N stress has been systematically studied, but the final response mechanism of ammonia-N affecting the immune system remains unclear. To investigate the relationship among immune factors of Litopenaeus vannamei (L. vannamei) exposed to 0, 2, 10 and 20 mg/L ammonia-N, the determination of complement components, C-type lectins, proPO system, signal transduction pathway and phagocytosis as well as exocytosis were performed. The results showed that the expressions of complement components including C1q, MBL, ficolin and alpha-2 macroglobulin (A2M) and the complement receptor integrin were decreased significantly in ammonia-N treatment groups at 6,12 and 24 h. C-type lectins and signal transduction factors changed significantly. The decrease of phagocytosis-related genes and phagocytic activity were similar to the changes of complement components, C-type lectins and the signal pathway. The mRNA abundance of exocytosis-related genes was significantly down-regulated under ammonia-N exposure. Correspondingly, significantly changes occurred in the expressions of PPAE and PPO3, immune factors-related genes (Pen3, crustin, stylicins, ALFs and LYC) and inflammatory factors (HSP90, TNFα, IL-16) in haemocytes. Eventually, the serine proteinase activity, PO activity, antibacterial activity and bacteriolytic activity in plasma were decreased significantly. In addition, we speculated that under ammonia-N stress, phagocytosis and exocytosis were affected by complement components, and C-type lectins through intracellular signal transduction pathway. Complement components may involve in the regulation of proPO-activating system to response to ammonia-N stress. This study helped to further understanding the relationship among immune factors of crustacean in response to environmental stress, which implied that when it comes to the decrease of immunity affected by environmental stress, we should not only focus on the mechanism of upstream neuroendocrine response, but also pay attention to the role of immune factors.

The injection of one recombinant C-type lectin (LvLec) induced the immune response of hemocytes in Litopenaeus vannamei

To explore the immune function of C-type lectin in shrimp, one recombinant C-type lectin (LvLec) was injected into Litopenaeus vannamei. There were four treatments in the experiment: saline group (as control group), recombinant C-type lectin group (LvLec, 1 mg mL^-1), Vibrio harveyi group (V. harveyi, 10⁶ cfu mL^-1) and recombinant C-type lectin combined with Vibrio harveyi group (LvLec + V. harveyi, 1 mg mL^-1 + 10⁶ cfu mL^-1). The sampling time was set at 0, 3, 6, 9, 12, 24 h after the injection. The results showed that the total hemocyte count decreased significantly and the phagocytic activity improved notably after the injection of LvLec, V. harveyi or LvLec + V. harveyi. Prophenoloxidase (proPO) activity decreased, while phenoloxidase (PO) activity increased and the changing degree of each group exhibited a significant difference. The hemagglutinating activity and bacteriolytic activity improved significantly, while the antimicrobial activity did not show a remarkable change in all of the groups. There were also changes that occurred in the levels of second messengers (cAMP, cGMP) and protein kinase (PKA, PKG). After the injection of LvLec, V. harveyi or LvLec + V. harveyi, the concentration of cGMP and PKA increased significantly, while the concentration of cAMP and PKG did not change remarkably. The results above suggested that rLvLec could induce nonspecific immune response, including phagocytosis, release of PO, hemagglutination and bacteriolysis through cGMP-PKA pathway in vivo.

A novel C-type lectin LvCTL 4.2 has antibacterial activity but facilitates WSSV infection in shrimp (L. vannamei)

Glycan-binding protein C-type lectin (CTL), one of the pattern recognition receptors (PRRs), binds to carbohydrates on the surface of pathogens and elicits antimicrobial responses in shrimp innate immunity. The objective was to identify and characterize a novel C-type lectin LvCTL 4.2 in Litopenaeus vannamei. The LvCTL 4.2 protein consisted of a signal peptide at the N terminal and a carbohydrate-recognition domain (CRD) with a mutated mannose-binding (Glu-Pro-Ala; EPA) motif at the C terminal, and thereby has a putative secreted mannose-binding C-type lectin architecture. LvCTL 4.2 was highly expressed in nervous tissue and stomach. Infection with white spot syndrome virus (WSSV) induced expression of LvCTL 4.2 in shrimp stomach at 12 h post infection. Conversely, there was no obvious upregulation in expression of LvCTL 4.2 in stomach or hepatopancreas of shrimp with AHPND (acute hepatopancreas necrosis disease). Pathogen binding assays confirmed recombinant LvCTL 4.2 protein (rLvCTL 4.2) had significant binding ability with the WSSV virion, Gram-negative, and Gram-positive bacteria. Moreover, rLvCTL 4.2 had strong growth inhibition of Vibrio parahaemolyticus. Silencing LvCTL 4.2 suppressed WSSV replication, whereas pretreatment of WSSV with rLvCTL 4.2 facilitated viral replication in vivo. In conclusion, LvCTL 4.2 acted as a PRR that inhibited AHPND-causing bacteria, but facilitated WSSV pathogenesis.

Antibacterial activity of four recombinant carbohydrate recognition domain proteins identified from the kuruma shrimp Marsupenaeus japonicus

The carbohydrate recognition domain (CRD) is the key component of C-type lectins (CTLs) with the capacity to recognize and eliminate invading pathogens. Herein, the recombinant proteins of four CRDs identified from the kuruma shrimp, Marsupenaeus japonicus, were produced and purified by an Escherichia coli expression system and affinity chromatography. Bacterial binding and antibacterial assays showed that the four CRDs displayed various bacterial binding and antibacterial activities against different bacteria. Among the four recombinant CRDs, His-CRD2-3 exhibited the broadest spectrum of bacterial binding and antibacterial activities against gram-negative bacteria (Vibrio parahaemolyticus, V. alginolyticus and V. harveyi) and gram-positive bacteria (Staphylococcus aureus and Micrococcus lysodeikticus). Moreover, the four recombinant CRDs showed different capacities to regulate the expression of several immune effector genes (MjCTL3, MjCTL4, MjCTL, Mjily and Mjsty), among which His-CRD2-3 displayed broader and stronger inductive effects on these immune effector genes. This study indicated that the four CRDs participated in immune defense by binding and killing bacteria and regulating the transcription of other immune effector genes. In addition, our results suggested that His-CRD2-3 might be a promising agent for the prevention and treatment of bacteriosis.

Proteomic analysis of hemocyte reveals the immune regulatory mechanisms after the injection of corticosteroid-releasing hormone in mud crab Scylla Paramamosain

Corticosteroid-releasing hormone (CRH) is a crucial neuroendocrine-immune factor regulating the immune response of Scylla paramamosain. To understand the regulatory mechanisms of CRH in S. paramamosain, the hemolymph of S. paramamosain with injection of CRH (1.5 ng/crab) at 24 h were chosen to perform proteomic analysis in this study. Furthermore, quantitative real-time PCR (RT-PCR) method was used to validate the accuracy of proteomic data at 24 h after CRH injection. The proteomic data showed that 255 DEPs were identified, in which 231 and 24 were up- or down-regulated, respectively. Besides, the results of enriched pathways showed that the DEPs were involved in signaling pathways, cellular immunity, humoral immunity and the response of immune related processes. These results revealed that CRH promoted the activation of signal transduction, regulated immune systems and antioxidation, and enhanced the immune related processes (such as protein synthesis, protein transport, carbohydrate mobilization and energy redistribution). These findings will benefit to foster the understanding on the effects of glucocorticoids on neuroendocrine-immune (NEI) networks of crustacean, and supply a substantial material and foundation for further researching of the NEI response. SIGNIFICANCE: Corticotrophin-releasing hormone (CRH) is a 41-amino acid neuropeptide and has been preliminarily studied in aquatic animals. CRH can regulate many important physiological activities comprising protein synthesis, energy metabolism, growth, breeding and behavior in fish, which play an important roles in neuroendocrine-immune (NEI) regulatory network of fish. The neuroendocrine system of crustacean has a primary research, that inspired by fish NEI network. Despite the research on the neuroendocrine system in crustacean has rapidly increased in recent years, our understanding of the regulation between neuroendocrine system and immune system in crustacean is still limited. The research on the strategy of NEI network in crustaceans becomes a significant issue. In the present study, the isobaric tags for relative and absolute quantification (iTRAQ) technology approach were applied to examine the NEI network of Scylla Paramamosain. control group and treatment group (CRH: 1.5 ng/crab) were settled for the iTRAQ experiment, and sampled at 24 h after CRH injection. The study aimed to gain knowledge on the immune response in Scylla Paramamosain after CRH injection and identify related differentially expressed proteins (DEPs) of the crab. The results of this study provide a preliminary resource for analysis the immune mechanism for crustaceans. In general, our work represents the first report of the utilization of the iTRAQ proteomics method for the study of NEI regulatory network in Scylla Paramamosain after CRH injection. We identified a number of DEPs involved in diverse pathways including immune signaling pathways, cellular immunity, humoral immunity, immune related process. These results demonstrated a very complex network involving immune and multiple related metabolic pathways in hemocytes of Scylla Paramamosain and will be of great value in understanding the crab neuroendocrine-immune immune mechanism.

Expression analysis of immune-associated genes in hemocytes of mud crab Scylla paramamosain under low salinity challenge

To gain knowledge on the immune response in Scylla paramamosain under low salinity challenge, S. paramamosain we investigated digital gene expression (DEG) in S. paramamosain hemocytes using the deep-sequencing platform Illumina Hiseq XTen. A total of 97,257 high quality unigenes with mean length 786.59 bp were found to be regulated by low salinity challenge, among which 93 unigenes were significantly up regulated, and 71 were significantly down regulated. Functional categorization and pathways analysis of differentially expressed genes revealed that immune signaling pathway including cAMP and cGMP signaling pathway were affected in low salinity stress. Cellular immunity-related genes including low-density lipoprotein receptor-related protein 6 (LRP6) and xanthine dehydrogenase (XDH) were down-regulated, indicating phagocytosis and oxygen dependent mechanism of phagocyte were suppressed in low salinity stress; Humoral immunity-related genes serine proteases and serpins 3 were up- and down-regulated, respectively, suggest that the proPO system was influenced by low salinity significantly; Moreover, processes related to immune response including carbohydrate metabolism, protein synthesis and lipid transport were found differentially regulated, implying the integrity of the immune response in low salinity stress. This study gained comprehensive insights on the immune mechanism of S. paramamosain at low salinity stress at the molecular level. The findings provide a theoretical basis for understanding immune mechanisms of S. paramamosain under low salinity stress, and technical reference for evaluating physiological adaptation in fresh water environment.

Antimicrobial properties and immune-related gene expression of a C-type lectin isolated from Pinctada fucata martensii

C-type lectins are carbohydrate-binding proteins that play important roles in the innate immune response to pathogen infections. Here, multi-step high performance liquid chromatography (HPLC), combined with mass spectrometry (MS), was used to isolate and identify proteins with antibacterial activity from the serum of Pinctada fucata martensii. Using this method, we obtained a novel isoform of C-type lectin (PmCTL-1). PmCTL-1 strongly inhibited gram-positive bacteria. The complete cDNA sequence of PmCTL-1 was 636 bp in length, and encoded a protein 149 amino acids long, containing a typical carbohydrate recognition domain (CRD). A phylogenetic analysis based on a multiple sequence alignment indicated that PmCTL-1 was highly similar to C-type lectins from other mollusks. Fluorescent quantitative real-time PCR analysis showed that PmCTL-1 mRNA was strongly upregulated in the mantle of healthy P.f. martensii, but was expressed only at low levels in the gill, gonad, hepatopancreas, adductor muscle, and hemocytes. PmCTL-1 expression levels in the mantle and hemocytes increased significantly in response to bacterial stimulation. This study provides a valuable framework for further explorations of innate immunity and the immune response in mollusks.

Peculiarities of innate immune memory in crustaceans

Classical characteristic of the innate immune system is the lack of ability to build up immunological memory, contrast to the adaptive immune system that is capable of "remembering" antigens, and rapidly mount a greater magnitude of immune response upon subsequent exposure to the same antigens. Peculiarly, immunological memory of innate immunity is evidenced in invertebrates. At least three different memory phenomena have been described, namely sustained unique response, recalled response, and immune shift. Studies attended to decipher the mechanistic biology of the innate immune memory reveals the role of epigenetics, which modulates the response of immune memory, and the heritability of immune memory to subsequent generations. A parthenogenetic Artemia model demonstrated successful transgenerational epigenetic inheritance of resistance trait against Vibrio campbellii. Following, the role of invertebrate hemocytes and Down syndrome cell adhesion molecule (Dscam) in innate immune memory is reviewed. While there is no vertebrate antibody homolog found in invertebrates, Dscam was found to resemble the functionality of vertebrate antibody. Insight of Dscam as immune factor was illustrated further in the current review.

The functional relevance of shrimp C-type lectins in host-pathogen interactions

C-type lectins (CTLs) are key recognition proteins in shrimp immunity. A few years ago we reviewed sequence information, ligand specificity, expression profiles and specific functions of the shrimp CTLs. Since then, multiple integrated studies that implemented biochemical approaches using both the native and recombinant proteins, functional genetic approaches using RNA interference, and mechanistic studies by analyzing protein-protein interactions were carried out. Results from these rigorous studies revealed the functions and mechanisms of action of selected members of the shrimp CTL family. This review focuses on this new knowledge, that includes unique structural aspects, functions, and mechanisms in host-pathogen interactions, the functional relevance of regions other than the C-type lectin domain, and the regulation of transcription of shrimp CTLs. Thus, this review aims to provide a detailed update of recent studies that have contributed to our better understanding of the shrimp immune events that involve CTL functions.

The mechanism of Mitogen-Activated Protein Kinases to mediate apoptosis and immunotoxicity induced by Benzo[a]pyrene on hemocytes of scallop Chlamys farreri in vitro

Benzo [a]pyrene (B [a]P) has received widespread attention for serious pollution in the sea, which may reduce immunity and lead to the outbreak of disease in bivalves. However, the mechanism of immunotoxicity induced by B [a]P in bivalves was still unclear. Previous studies have found that Mitogen-Activated Protein Kinases (MAPKs) including three classic pathways (ERK, p38 and JNK) play an important role in mediating this process. Thus, in order to explore the mechanism of immunotoxicity induced by B [a]P in scallop Chlamys farreri, hemocytes were treated with PD98059 (ERK inhibitor), SB203580 (p38 inhibitor) and SP600125 (JNK inhibitor) for 1 h and then incubation with B [a]P for 24 h at 1 μg/mL. Indexes including oxidative damage, apoptotic rate, and immune indicators were detected in the present study. The results showed that the increase of Reactive Oxygen Species (ROS) and DNA damage induced by B [a]P was inhibited with PD98059 and SB203580. Besides, lysosomal membrane stability (LMS) damage was promoted by PD98059, while it was opposite when treated with SB203580. Moreover, the ascended apoptosis rate induced by B [a]P was increased significantly after treatment with PD98059, but it was remarkably attenuated by SB203580 and SP600125. However, the opposite pattern was showed in phagocytosis compared with apoptosis rate in all of three inhibitors. In addition, antibacterial activity and bacteriolytic activity were enhanced by SB203580 while inhibited by PD98059. Therefore, these results showed that MAPKs directly or indirectly mediate the decrease of oxidative damage, apoptosis and immune defense ability of C. farreri hemocytes, which suggesting ERK/p38/JNK pathways have different functions in the apoptosis and immunity of C. farreri hemocytes after B [a]P exposure. In conclusion, this study intended to enrich the theoretical basis for immunotoxicology of bivalves exposed to pollutants.

Transcriptome analysis and immune-related genes expression reveals the immune responses of Macrobrachium rosenbergii infected by Enterobacter cloacae

Macrobrachium rosenbergii is an important cultural species in China and other Southeast Asian countries. However, Enterobacter cloacae infection has caused a great economic loss in M. rosenbergii culture industry. The immune responses of M. rosenbergii to the E. cloacae infection is not fully characterized. To investigate the immune response of M. rosenbergii against E. cloacae, we performed transcriptome analysis of the M. rosenbergii hepatopancreas with and without E. cloacae infection using RNA-seq. After assembly and annotation, 29,731 high quality unigenes were obtained from RNA-seq data. Differential expression analysis revealed the existence of 2498 significantly differently expressed genes (DEGs) at 12 h post infection, with 1365 up-regulated and 1133 down-regulated genes. Among these DEGs, some well-known immune-related genes were up-regulated significantly, including C-type lectin 1, lectin 3, anti-lipopolysaccharide factor 2, Cu/Zn superoxide dismutase and heat shock protein 70. GO analysis demonstrated 24 biological process subcategories, 14 cellular component subcategories, and 12 molecular function subcategories that were enriched among these DEGs, and some DEGs were clustered into immune related subcategories such as immune system process, response to stimulus, biological adhesion, and antioxidant activity. These DEGs were enriched into 216 KEGG pathways including a core set of immune correlated pathways notably in phagosome and lysosome. In addition, 5 up-regulated and 5 down-regulated immune-related DEGs were selected for further validation by quantitative real-time PCR and the results showed consistence with the RNA-seq data. Additionally, the expression level of six selected immune-related genes (ALF2, CLEC1, LEC3, hemocyanin1, HSP70 and SOD) based on the transcriptomic data were monitored at different point of time in hepatopancreas, gill, hemolymph and intestine. Results revealed these immune-related genes were significantly up-regulated in different tissues from 6 to 24 h after E. cloacae infection. Overall, these results provided valuable information for further studying the immune response of M. rosenbergii against E. cloacae infection.

A novel C-type lectin with a YPD motif from Portunus trituberculatus (PtCLec1) mediating pathogen recognition and opsonization

C-type lectins are a superfamily of Ca²⁺-dependent carbohydrate-recognition proteins that function as pattern recognition receptors (PRRs) in innate immune system. In this study, a new C-type lectin was identified from the swimming crab Portunus trituberculatus (PtCLec1). The full-length cDNA of PtCLec1 was 873 bp encoding 176 amino acids. The predicted PtCLec1 protein contained a signal peptide and a single carbohydrate-recognition domain with a special YPD motif. The PtCLec1 transcripts were mainly detected in hepatopancreas and its relative expression levels were significantly up-regulated after the challenges of Vibrio alginolyticus, Micrococcus luteus and Pichia pastoris. The recombinant PtCLec1 (rPtCLec1) could bind all the tested pathogen-associated molecular patterns (PAMPs), including lipopolysaccharides (LPS), peptidoglycan (PGN) and glucan (GLU), and microorganisms, including V. alginolyticus, V. parahaemolyticus, Pseudomonas aeruginosa, Staphylococcus aureus, M. luteus and P. pastoris. It also exhibited strong activity to agglutinate bacteria and yeast in a Ca²⁺-dependent manner, and such agglutinating activity could be inhibited by d-galactose and LPS. Moreover, rPtCLec1 revealed antimicrobial activity against the tested Gram-negative (V. alginolyticus, V. parahaemolyticus and P. aeruginosa) and Gram-positive bacteria (S. aureus and M. luteus), and promoted the clearance of V. alginolyticus in vivo and hemocyte phagocytosis in vitro. Knockdown of PtCLec1 could down-regulate the expression of phagocytosis-related genes, but enhance the expression levels of prophenoloxidase (proPO) system-related genes, mannose-binding lectin (MBL), antimicrobial peptides (AMPs), MyD88 and Relish. All these results indicate that PtCLec1 might act as a PRR in immune recognition and an opsonin in pathogen elimination.

Hemocyte-Mediated Phagocytosis in Crustaceans

Phagocytosis is an ancient, highly conserved process in all multicellular organisms, through which the host can protect itself against invading microorganisms and environmental particles, as well as remove self-apoptotic cells/cell debris to maintain tissue homeostasis. In crustacean, phagocytosis by hemocyte has also been well-recognized as a crucial defense mechanism for the host against infectious agents such as bacteria and viruses. In this review, we summarized the current knowledge of hemocyte-mediated phagocytosis, in particular focusing on the related receptors for recognition and internalization of pathogens as well as the downstream signal pathways and intracellular regulators involved in the process of hemocyte phagocytosis. We attempted to gain a deeper understanding of the phagocytic mechanism of different hemocytes and their contribution to the host defense immunity in crustaceans.

Transcriptome analysis of hemocytes from the white shrimp Litopenaeus vannamei with the injection of dopamine

As a crucial neuroendocrine-immune factor, dopamine (DA) could regulate the immune system of Litopenaeus vannamei. To understand the immune mechanisms and regulatory pathways of DA in L. vannamei, the transcriptome analysis of hemocytes of L. vannamei with injection of DA (10^-6 mol/shrimp) at 3 and 12 h were performed in this study. Moreover, quantitative real-time PCR (qPCR) method was applied to validate the accuracy of transcriptome sequencing and analyze the expression pattern of candidate differentially expressed genes (DEGs) at different time points (0, 3, 6, 12, and 24 h) after DA injection. The results showed that a total of 51382 unigenes with a N50 length of 2341 bp were generated. And 1397 and 457 DEGs were obtained by comparative transcriptome at 3 and 12h respectively. Moreover, the results of functional annotation and enriched pathway showed that the DEGs were involved in phagosome (ko04145), lysosome (ko04142), Endocytosis (ko04144), and NOD-like receptor signaling pathway (ko04621). Besides, the Pearson's correlation coefficient (R) between transcriptome sequencing and qPCR was 0.845, which confirmed the reliability of the transcriptome sequencing results and the accuracy of assembly. Furthermore, the expression pattern of 15 candidate DEGs, containing 9 up-regulated and 6 down-regulated DEGs at 3 h, indicated the regulation of DA in physiological functions especially in the immune system. Therefore, these results revealed that DA induced the expressions of membrane receptors or proteins, activated intracellular signaling pathways, regulated cellular and humoral immune systems, controlled antioxidation and apoptosis, and was involved in the regulation of neuroendocrine system. These findings are helpful to promote the understanding on the effects of biogenic amines on physiological functions and regulatory networks of crustacean, and offer a substantial material and foundation for researching the immune response of crustacean.

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.