Molecular cloning and characterization of a receptor for activated protein kinase C1 (RACK1) from Chinese white shrimp; Fenneropenaeus chinensis

Receptor for activated C kinase 1 (RACK1), which has seven tandem WD40 domains, is a scaffolding protein. RACK1 plays different roles by binding to different partner proteins. It is involved in hormone signaling and development, and now some evidence indicates it may have a role in innate immunity. In this paper, RACK1 cDNA from Chinese white shrimp (FcRACK1) was identified. The full length of the FcRACK1 gene is 1037 bp, including a 30 bp 5′UTR, a 957 bp ORF encoding a 318 amino acid protein, and a 50 bp 3′UTR with the polyadenylation sequence AATAAA and a poly (A) tail. The FcRACK1 protein is characterized by seven WD40 repeat domains; the ending two amino acids of each WD40 domain are WK, WD, WN, WS, WD, WD, and WQ, respectively. The length of each domain is between 30 and 44 amino acids. Multiple alignments of RACK1s showed that RACK1s are highly conserved. RT-PCR showed that FcRACK1 could be detected in hemocytes, the heart, hepatopancreas, gills, stomach, intestine, and ovary. FcRACK1 in hemocytes was down-regulated after a 2 h WSSV challenge, and FcRACK1 in gills was up-regulated after a 2 h Vibrio challenge. FcRACK1 in ovary went down after a 12 h Vibrio challenge and then up-regulated at 24 h. FcRACK1 in ovary was first down-regulated at 2 h after a WSSV challenge and then up-regulated to the highest level at 6 h. It finally went down from 12 to 24 h. In hepatopancreas, FcRACK1 was also up-regulated by microbe challenge. Our results indicated its probable role in shrimp innate immunity.     

The role of ficolin-like protein (PcFLP1) in the antibacterial immunity of red swamp crayfish (Procambarus clarkii)

In invertebrates, ficolin-like proteins (FLPs) play important roles in innate immunity against pathogens. Previous studies primarily investigated the functions of FLPs in immune recognition, activation, and regulation. However, limited research has examined the functions of FLPs as immune effectors. In this work, a ficolin-like protein was identified in red swam crayfish (Procambarus clarkii) and designated as PcFLP1. Quantitative RT-PCR and western blot were employed to analyze the distribution and expression profiles of PcFLP1 in the tissues of the crayfish. The results indicated that PcFLP1 was present in all tested tissues, including hemocytes, heart, hepatopancreas, gill, stomach, and mid-intestine. The expression level of PcFLP1 was up-regulated in hemocytes, hepatopancreas and mid-intestines of the crayfish challenged with Vibrio parahaemolyticus. Further study demonstrated that PcFLP1 could protect the hepatopancreatic cells of crayfish from V. parahaemolyticus infection. The recombinant PcFLP1 enhanced bacterial elimination in crayfish, whereas the antibacterial action was inhibited after PcFLP1 was knocked down. Furthermore, PcFLP1 could bound to bacteria and inhibited bacterial replication. These results demonstrated that PcFLP1 plays an important role in the anti-Vibrio immunity of red swamp crayfish.     

The specifically enhanced cellular immune responses in Pacific oyster (Crassostrea gigas) against secondary challenge with Vibrio splendidus

The increasing experimental evidences suggest that there are some forms of specific acquired immunity in invertebrates, but the underlying mechanism is not fully understood. In the present study, Pacific oyster (Crassostrea gigas) stimulated primarily by heat-killed Vibrio splendidus displayed stronger immune responses at cellular and molecular levels when they encountered the secondary challenge of live V. splendidus. The total hemocyte counts (THC) increased significantly after the primary stimulation of heat-killed V. splendidus, and it increased even higher (p < 0.01) and reached the peak earlier (at 6 h) after the secondary challenge with live V. splendidus compared with that of the primary stimulation. The number of new generated circulating hemocytes increased dramatically (p < 0.01) at 6 h after the pre-stimulated oysters received the secondary stimulation with live V. splendidus, and the phagocytic rate was also enhanced significantly (p < 0.01) at 12 h after the secondary stimulation. Meanwhile, the enhanced phagocytosis of hemocytes was highly specific for V. splendidus and they could distinguish Vibrio anguillarum, Vibrio coralliilyticus, Yarrowia lipolytica, and Micrococcus luteus efficiently. In addition, the mRNA expression of 12 candidate genes related to phagocytosis and hematopoiesis were also monitored, and the expression levels of CgIntegrin, CgPI3K (phosphatidylinositol 3-kinase), CgRho J, CgMAPKK (mitogen-activated protein kinase kinase), CgRab32, CgNADPH (nicotinamide adenine dinucleotide phosphate) oxidase, CgRunx1 and CgBMP7 (bone morphogenetic protein 7) in the hemocytes of pre-stimulated oysters after the secondary stimulation of V. splendidus were higher (p < 0.01) than that after the primary stimulation, but there was no statistically significant changes for the genes of CgPKC (protein kinase C), CgMyosin, CgActin, and CgGATA 3. These results collectively suggested that the primary stimulation of V. splendidus led to immune priming in oyster with specifically enhanced phagocytosis and rapidly promoted regeneration of circulating hemocytes when the primed oysters encountered the secondary challenge with V. splendidus.     

Characterization of the circulating hemocytes in mud crab (Scylla olivacea) revealed phenoloxidase activity

This study focused on an isolation and characterization of the circulating hemocytes in mud crab, Scylla olivacea. Isolation of specific cell types of hemocytes from crab hemolymph was accomplished by using 60% Percoll density gradient centrifugation. Four separated bands of the hemocytes were successfully obtained. Characterization of these isolated hemocytes by light microscope using trypan blue-rose bengal staining, rose bengal–hematoxilin staining, and phase contrast revealed four distinct types of hemocyte cells. Using their specific morphology and granularity, they were identified as hyaline cell (HC), small granular cell (SGC), large granular cell (LGC) and mixed granular cell (MGC). Transmission electron microscopy (TEM) revealed more details on specific cell size, size of cytoplasmic granule, and nuclear to cytoplasmic ratio, and confirmed the classification. Relative abundance of these cells types in the hemolymph of an adult crab were 15.50 ± 8.22% for HC, 55.50 ± 7.15% for SGC, 13.50 ± 5.28% for LGC, and 15.50 ± 3.50% for MGC. Proteomic analysis of protein expression for each specific cell types by two-dimensional electrophoresis identified two highly abundant proteins, prophenoloxidase (ProPO) and peroxinectin in LGC. Determination of phenoloxidase (PO) activity in each isolated cell types using in vitro and in situ chemical assays confirmed the presence of PO activity only in LGC. Based on an increased PO activity of crab hemolymph during the course of White Spot Syndrome Virus (WSSV) infection, these results suggest that prophenoloxidase pathway was employed for host defense mechanism against WSSV and it may link to the role of large granular hemocyte.     

Litopenaeus vannamei tumor necrosis factor receptor-associated factor 6 (TRAF6) responds to Vibrio alginolyticus and white spot syndrome virus (WSSV) infection and activates antimicrobial peptide genes

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) is a key signaling adaptor protein not only for the TNFR superfamily but also for the Interleukin-1 receptor/Toll-like receptor (IL-1/TLR) superfamily. To investigate TRAF6 function in invertebrate innate immune responses, Litopenaeus vannamei TRAF6 (LvTRAF6) was identified and characterized. The full-length cDNA of LvTRAF6 is 2823 bp long, with an open reading frame (ORF) encoding a putative protein of 594 amino acids, including a RING-type Zinc finger, two TRAF-type Zinc fingers, a coiled-coil region, and a meprin and TRAF homology (MATH) domain. The overall amino acid sequence identity between LvTRAF6 and other known TRAF6s is 22.2-33.3%. Dual luciferase reporter assays in Drosophila S2 cells revealed that LvTRAF6 could activate the promoters of antimicrobial peptide genes (AMPs), including Drosophila Attacin A and Drosomycin, and shrimp Penaeidins. Real-time quantitative PCR (qPCR) indicated that LvTRAF6 was constitutively expressed in various tissues of L. vannamei. After Vibrio alginolyticus and white spot syndrome virus (WSSV) challenge, LvTRAF6 was down-regulated, though with different expression patterns in the intestine compared to other tissues. After WSSV challenge, LvTRAF6 was up-regulated 2.7- and 2.3-fold over the control at 3 h in gills and hepatopancreas, respectively. These results indicated that LvTRAF6 may play a crucial role in antibacterial and antiviral responses via regulation of AMP gene expression.     

Granulocytes of the red claw crayfish Cherax quadricarinatus can endocytose beads, E. coli and WSSV,but in different ways

The hemocytes of the red claw crayfish Cherax quadricarinatus are classified by morphologic observation into the following types: hyalinocytes (H), semi-granulocytes (SG) and granulocytes (G). Density gradient centrifugation with Percoll was developed to separate these three subpopulations of hemocytes. Beads, Escherichia coli, and FITC labeling WSSV were used to investigate the characteristics of granulocytes by using scanning electron microscope, transmission electron microscope, and laser scan confocal microscope. Results showed that granulocytes could phagocytose beads and E. coli by endocytic pathways. WSSV could rely on caveolae-mediated endocytosis to mainly enter into granulocytes. These results could elucidate the mechanism of the innate immunity function of granulocytes, and it also showed the mechanism by which WSSV invaded granulocytes in the red claw crayfish.     

A vector that expresses VP28 of WSSV can protect red swamp crayfish from white spot disease

White spot disease caused by white spot syndrome virus (WSSV) leads to devastating losses in shrimp farming. The WSSV envelope protein VP28, can be used as subunit vaccines that can efficiently protect shrimp against WSSV disease. However, the function of the envelope protein VP19 was not confirmed, some researches found that VP19 could protect shrimp against WSSV, and other reports found it no any protection. To detect the functions of VP28 and VP19 and find a method to prevent this disease in red swamp crayfish Procambarus clarkii, we constructed the plasmid vectors pIevp28 and pIevp19, which contains the ie1 promoter and coding region of vp28 or vp19 of WSSV, respectively. The results of quantitative real-time PCR and western blot showed that the injected vectors could transcribe corresponding mRNAs and translate to the protein VP28 or VP19 in the crayfish. The vp28 or vp19 signal was detected on the third day post injection, and maintained its expression for 30 days. The mortality of the crayfish with pIevp28 showed obvious decline compared with the controls (pIe and PBS injection). However, pIevp19 seems did not affect the mortality of the crayfish compared with the controls. Furthermore, only VP28 was found tightly bound to the host haemocytes under immunocytochemistry. The results suggest that the VP28 protein might protect shrimp from the virus through competitive inhibition. We also found that oral administration of Escherichia coli with pIevp28 could protect crayfish from white spot disease, but the E. coli with pIevp19 was not. Therefore, we think that oral administration of bacteria with pIevp28 is a potentially easy therapeutic way against white spot disease in aquaculture.     

Identification and characterization of a QM protein as a possible peptidoglycan recognition protein (PGRP) from the giant tiger shrimp Penaeus monodon

In an attempt to identify a peptidoglycan recognition protein (PGRP) in Penaeus (Penaeus) monodon, in vitro pull-down binding assays were used between shrimp proteins and purified peptidoglycan (PG). By gel electrophoresis and mass spectrometry followed by Mascot program analysis, proteins from shrimp hemocyte peripheral membrane proteins showed significant homology to records for a QM protein, actin and prophenoloxidase 2 precursor (proPO2), while proteins from cell-free plasma showed significant homology to records for a vitellogenin, a fibrinogen related protein (FREP) and a C-type lectin. Due to time and resource limitations, specific binding to PG was examined only for recombinant PmQM protein and PmLec that were synthesized based on sequences reported in the Genbank database (accession numbers FJ766846 and DQ078266, respectively). An in vitro assay revealed that hemocytes would bind with and encapsulate agarose beads coated with recombinant PmQM (rPmQM) or rPmLec and that melanization followed 2 h post-encapsulation. ELISA tests confirmed specific binding of rPmQM protein to PG. This is the first time that PmQM has been reported as a potential PGRP in shrimp or any other crustacean. The two other potential PGRP identified (FREP and the vitellin-like protein present in male P. monodon, unlike other vitellin subunits) should also be expressed heterologously and tested for their ability to activate shrimp hemocytes.     

Association of HLA-DRB1 and TNF genotypes with dengue hemorrhagic fever

Genes coding for human leukocyte antigen (HLA) class II molecules and tumor necrosis factor (TNF)-α are polymorphic and have been shown to influence susceptibility to infectious diseases. In the present study, HLA-DRB1, -DQB1 and TNF gene polymorphisms were investigated in 114 dengue patients (DEN) [85 dengue fever (DF) cases and 29 dengue hemorrhagic fever (DHF) cases] and 110 healthy controls (HCs) using PCR based methods. The frequencies of HLA-DRB1^∗07 allele [DF vs. DHF, P = 0.0034, Pc = 0.044, OR 3.79] and HLA-DRB1^∗07/^∗15 genotype [DF vs. DHF, P = 0.00071, Pc = 0.038, OR 10.41] were significantly higher in DHF cases as compared to HCs and DF cases. Higher frequency of rs1800629 ‘G/A’ genotype was observed in DHF cases as compared to DF cases. The frequency of rs1799964 ‘C/C’ genotype of the TNF gene was found to be significantly higher in all patient groups compared to HCs [HCs vs. DEN, P = 0.0054, Pc = 0.0162, OR 3.57; HCs vs. DF, P = 0.036, OR 2.89; HCs vs. DHF, P = 0.0088, Pc = 0.0240, OR 5.11]. Presence of combination of HLA-DRB1^∗07/^∗15 with either rs1799964 ‘C/C’ genotype or rs1800629 ‘G/A’ genotype or both was present in 17.2% of DHF cases and 1.2% in HCs while this combination was not observed in DF cases. The results suggest that HLA-DRB1^∗07/^∗15 genotype in combination with TNF polymorphisms influence progression to DHF.     

Characterization of a Kunitz-type protease inhibitor (MjKuPI) reveals the involvement of MjKuPI positive hemocytes in the immune responses of kuruma shrimp Marsupenaeus japonicus

Serine proteases and their inhibitors play vital roles in biological processes. Serine protease inhibitors, including Kunitz-type protease inhibitors play important roles not only in physiological process (i.e. blood clotting and fibrinolysis) but also in immune responses. In this study, we characterized a Kunitz-type protease inhibitor, designated MjKuPI, from kuruma shrimp Marsupenaeus japonicus. An expression profile showed that MjKuPI was mainly expressed in hemocytes. Immunostaining revealed that some hemocytes expressed MjKuPI (MjKuPI⁺ hemocytes) and others did not (MjKuPI⁻ hemocytes). Injection of shrimp with Vibrio penaeicida and white spot syndrome virus (WSSV) upregulated the mRNA level of MjKuPI, and a flow cytometry analysis revealed that the proportion of MjKuPI⁺ hemocytes increased significantly 24 h after injection. Together, these results suggest that MjKuPI and MjKuPI⁺ hemocytes have a role in the innate immune system of kuruma shrimp.     

The immunomodulation of a novel tumor necrosis factor (CgTNF-1) in oyster Crassostrea gigas

Tumor necrosis factor (TNF) is one of the most important cytokines involved in many processes in both vertebrate and invertebrate. In the present study, a new tumor necrosis factor with a typical TNF domain was identified in oyster Crassostrea gigas (designated CgTNF-1). CgTNF-1 shared low sequence identity and similarity with the TNF superfamily members from other vertebrate and invertebrate. After LPS stimulation, the mRNA expression of CgTNF-1 in haemocytes increased significantly and peaked at 12 h (1.39 ± 0.12, P < 0.05) post treatment, and the expression of CgTNF-1 protein in haemolymph also increased obviously during 6–12 h. When the oyster haemocytes were incubated with rCgTNF-1, its apoptosis and phagocytosis rate were both effectively induced and peaked at 12 h post the treatment of rCgTNF-1 with the concentration of 100 ng mL⁻¹ (23.3 ± 3%, P < 0.01), 50 ng mL⁻¹ (5.3 ± 0.6%, P < 0.05) and 10 ng mL⁻¹ (6.7 ± 1.2%, P < 0.05), respectively. After the co-stimulation of LPS and rCgTNF-1, the apoptosis and phagocytosis rate of oyster haemocytes, and the activities of PO and lysozyme in the haemolymph all increased significantly, and reached the peak at 12 h (apoptosis rate 26.7 ± 1.5%, P < 0.01), 12 h (phagocytosis rate 8.3 ± 0.6%, P < 0.01), 6 h (PO 1.11 ± 0.01 U mg prot⁻¹, P < 0.01) and 12 h (lysozyme 168.9 ± 8.3 U mg prot⁻¹, P < 0.05), respectively, which were significantly higher than that in the LPS group. Furthermore, the anti-bacteria activity in the LPS + TNF group was significantly higher than that in the LPS group during 6–12 h. All the results collectively indicated that CgTNF-1 was involved in the oyster immunity and played a crucial role in the modulation of immune response including apoptosis and phagocytosis of haemocytes, and regulation of anti-bacterial activity as well as the activation of immune relevant enzymes.