Purification and functional characterization of serum transferrin from Nile tilapia (Oreochromis niloticus)

Skin mucus and blood plasma as non-lethal sources of malnutrition protein biomarkers in meagre (Argyrosomus regius)

Developing dietary formulations for aquaculture that meet nutritional requirements is essential to production, as nutrition is key for fish growth and health. However, novel dietary formulations may induce malnutrition, which is complex to evaluate and often requires animal sacrifice. Therefore, finding reliable non-lethal biomarkers to diagnose malnutrition in fish is important. This study aimed to obtain vital information on potential non-lethal biomarkers from blood plasma and skin mucus to assess the fish's nutritional status using meagre (Argyrosomus regius) juveniles. For that purpose, a nutritional challenge was performed with fish fed a fish meal (FM) and fish-oil (FO) based control diet (55.1 % FM; 11 % FO, CTRL), a challenging diet (15 % FM; 7 % FO, CD), and a highly challenging diet (5 % FM; 5 % FO, ED), which, despite being nutritionally complete, may pose digestive and physiological challenges to carnivorous species. Diets significantly affected blood parameters, except for leukocyte counts, peroxidase activity, and immunoglobulin levels. Overall, blood parameters showed potential as non-lethal biomarkers to accurately identify signs of malnutrition. Meagre's plasma and skin mucus proteomes provided crucial information on the species' reaction to malnutrition, and 29 proteins connected to various physiological functions such as metabolism, development and immunity showed potential as non-lethal biomarkers. SIGNIFICANCE: The significance of this study lies in the establishment of potential non-lethal biomarkers for diagnosing malnutrition in fish. The results demonstrate that immunological, haematological, and biochemical parameters measured in fish blood can reveal signs of nutritional deficiencies. The findings further highlight that the proteomes of plasma and skin mucus provide valuable information about the fish's nutritional status. Notably, 29 proteins identified in this study, associated with various physiological functions, exhibit biomarker potential and warrant consideration in future research in the field of aquaculture nutrition. Moreover, the research provides critical insights into the proteome of meagre (Argyrosomus regius), enhancing our understanding of the species and contributing to the future improvement of its aquaculture production.

MBL regulates phagocytosis and bactericidal activity of macrophages by triggering AKT/NF-κB/Rab5A axis occurred early in vertebrate evolution

Mannose-binding lectin (MBL) is a vital and versatile component of innate immunity, which plays an essential role in host defense. In mammals, MBL performs multiple functions, including pattern recognition, complement activation, and phagocytosis. Previous studies revealed that OnMBL can promote the opsonophagocytosis of macrophages through its interaction with calreticulin (CRT) in a complement activation-independent manner in Nile tilapia (Oreochromis niloticus). However, the oligomer structural characteristics of MBL and the pathways involved in immune defense mechanisms remain poorly understood. In this study, we identified different oligomer forms of OnMBL in tilapia serum, with significant increases in trimer and tetramer levels present following immunization with Streptococcus agalactiae. Further investigation demonstrated that a higher degree of OnMBL oligomerization enhanced its ability to bind and phagocytose bacteria. Notably, OnMBL promoted the formation of phagolysosomes, which are responsible for degrading and eliminating ingested bacteria. Additionally, OnMBL knockdown caused a marked downregulation of the CD91a postinfection. Moreover, it is confirmed that OnMBL interacted with OnCRT and OnCD91a, with OnCD91a being essential for the OnMBL/CRT complex to facilitate phagocytosis and bacterial clearance. Mechanistic studies revealed that OnMBL/CRT complex enhanced phagocytosis through collaboration with OnCD91a, triggering a positive feedback loop mediated by the AKT/NF-κB/Rab5A signaling axis, thereby boosting macrophage activities and antibacterial immune responses. Therefore, this study elucidates the antibacterial response mechanism of oligomer OnMBL and its receptor in early vertebrates. These findings add to the knowledge regarding the regulatory mechanisms of C-type lectins in fish and provide valuable insights into the evolution of innate immunity.

Transferrin from obscure puffer Takifugu obscurus promotes antimicrobial immune response

Transferrin (TF) is an iron-binding glycoprotein that plays a crucial role in host defense by restricting iron availability to pathogens and activating antimicrobial immune responses. However, its antimicrobial role in fish remains largely unexplored. In this study, we identified and characterized transferrin from obscure puffer Takifugu obscurus, named ToTF, and investigated its functions in bacterial infections. The coding region of the ToTF gene consists of 2295 bp, encoding a polypeptide of 764 amino acids. Tissue distribution analysis revealed that ToTF is primarily expressed in the liver. The mRNA expression of ToTF was significantly upregulated in both the liver and kidney following challenge with Staphylococcus aureus and Vibrio harveyi. Moreover, recombinant ToTF (rToTF) markedly inhibits iron-dependent bacteria growth, including S. aureus and V. harveyi. The iron-binding capacity of rToTF peaked at pH 8 and decreased significantly under acidic conditions. Furthermore, the antibacterial activity of rToTF peaked at near-neutral pH but decreased significantly at pH below 5. This dual mechanism deprives bacteria of essential iron through high-affinity binding and directly inhibits their growth under optimal conditions. These findings highlight the dual role of ToTF in the antibacterial immunity of T. obscurus, mediated by iron sequestration and direct bacteriostatic effects. This study supports the development of TF-based antibacterial agents and enhances strategies for aquatic disease prevention and fish disease resistance.

Elucidation on the Interaction Between Transferrin and Tetrachlorobisphenol A Based on Multispectroscopic Analysis, Molecular Docking Technique, and Conformational Studies

Tetrachlorobisphenol A (TCBPA) is a kind of fire retardant extensively used in our life, but it can accumulate in organisms and potentially have toxic effects. Transferrin (TF) is a glycoprotein predominantly present in the blood plasma, serving as an essential mediator for the transportation of iron and other small molecules. In our study, various techniques including multi-spectroscopic and molecular docking were employed to examine the interaction between TCBPA and TF. The TF-TCBPA complex was formed with the binding constant (Ka) in 2.181 ± 0.035 × 104 M-1 at 298 K. ΔH and ΔS were all negative, which means dominant driving forces were van der Waals forces and H-bonds. The secondary structure of TF was changed by TCBPA, resulting in a decline in the α-helix structure, and a corresponding increase in the β-sheet structure. The molecular docking revealed that TCBPA was positioned within a pocket of TF, and it engaged in interactions with some amino acid residues through different forces. Importantly, the interaction between Tyr426/Asp392/His585 and TCBPA implies that TCBPA potentially interferes with the transportation of iron ions in vivo. All of above results indicated the adverse effects of TCBPA on the TF structure and activity should be more attention.

The role of TF-b in iron homeostasis and bacterial defense in common carp (Cyprinus carpio)

Transferrin (TF) is a prototypical biological macromolecule protein known for its iron-binding properties. TF proteins play a crucial role in modulating host iron homeostasis and defending against pathogen invasion. In this study, we utilized common carp (Cyprinus carpio) tissues and Epithelioma papulosum cyprinid (EPC) cells to establish experimental models of iron overload with FeCl3 or ferric amine citrate (FAC), and to establish experimental models of bacterial infection with Aeromonas hydrophila. The current research has successfully identified the CcTF-b gene in common carp, revealing an ORF of 2001 bp with N-terminal and C-terminal structures. CcTF-b exhibited inhibitory effects on the growth of LPS and LTA in vitro. In the experimental models, the upregulations of PTGS2a and PTGS2a-like mRNA and protein levels were observed. Overexpression or interference with CcTF-b levels can modulate the expression of ferroptosis-related genes, inflammatory cytokines, lipid reactive oxygen species, GSH/GSSH levels, and Fe2+ concentration. Significantly, the expression levels of Nrf2 and GPX4 mRNA and protein, as well as the bacterial load of A. hydrophila, could be also modulated either by upregulating or downregulating CcTF-b factors. In conclusion, in this study, these findings suggest that CcTF-b plays a critical role in the innate immune response of common carp.

Transcriptome Analysis and Identification of Cadmium-Induced Oxidative Stress Response Genes in Different Meretrix meretrix Developmental Stages

Cadmium (Cd) is one of the major pollutants in the aquatic environment, and it can easily accumulate in aquatic animals and result in toxic effects by changing the metabolism of the body, causing a serious impact on the immune system, reproductive system, and the development of offspring. The clam Meretrix meretrix is one of the commercially important species that is cultivated in large-scale aquaculture in China. To elucidate the underlying molecular mechanisms of Cd2+ in the developmental processes, fertilized eggs and larvae of M. meretrix at different developmental stages were exposed to Cd2+ (27.2 mg L-1 in natural seawater) or just natural seawater without Cd2+ (control), and high-throughput transcriptome sequencing and immunohistochemistry techniques were used to analyze the toxic effects of Cd on larvae at different early developmental stages. The results revealed 31,914 genes were differentially expressed in the different stages of M. meretrix development upon treatment with Cd2+. Ten of these genes were differentially expressed in all stages of development examined, but they comprised only six unigenes (CCO, Ndh, HPX, A2M, STF, and pro-C3), all of which were related to the oxidative stress response. Under Cd exposure, the expression levels of CCO and Ndh were significantly upregulated in D-shaped and pediveliger larvae, while pro-C3 expression was significantly upregulated in the fertilized egg, D-shaped larva, and pediveliger. Moreover, HPX, A2M, and STF expression levels in the fertilized egg and pediveliger larvae were also significantly upregulated. In contrast, CCO, Ndh, HPX, A2M, STF, and pro-C3 expression levels in the postlarva were all downregulated under Cd exposure. Besides the genes with changes in expression identified by the transcriptome, the expression of two other oxidative stress-related genes (MT and Nfr2) was also found to change significantly in the different developmental stages of M. meretrix upon Cd exposure, confirming their roles in combating oxidative stress. Overall, the findings of this study indicated that Cd would interfere with cellular respiration, ion transport, and immune response through inducing oxidative stress, and changes in the expression of oxidative stress-related genes might be an important step for M. meretrix to deal with the adverse effects of Cd at different stages of its development.

Mannose-binding lectin suppresses macrophage proliferation through TGF-β1 signaling pathway in Nile tilapia

Mannose-binding lectin (MBL) is a multifunctional pattern recognition molecule, which not only mediates the recognition of pathogenic microorganisms and their products, playing an important role in innate immune defense, but also participates in adaptive immune responses of mammalian. However, it's related immune mechanism remains limited, especially the regulation of cell proliferation in early vertebrates. In this study, OnMBL was found to bind to kidney macrophages (MФ) from Nile tilapia (Oreochromis niloticus). Interestingly, OnMBL was able to reduce the proliferation of activated-MФ by regulating the cell cycle, arresting a large number of cells in the G0/G1 phase, and increasing the probability of apoptosis. More importantly, we found that the inhibition of cell proliferation by OnMBL was closely related to the evolutionarily conserved canonical transforming growth factor-beta 1 (TGF-β1) signaling pathway. Mechanistically, OnMBL could significantly increase the expression of TGF-β1, activate and regulate the downstream Smad-dependent pathway to reduce the MФ proliferation, thereby maintaining cellular homeostasis in the body's internal environment. This study represents the first description regarding the regulatory mechanisms of the MBL on cell proliferation in teleost fish, which provides a novel perspective on the understanding of the multiple function and evolutionary origins of C-type lectins in the immune system.

C9 regulates the complement-mediated cell lysis in association with CD59 to resist bacterial infection in a primary animal

Complement component 9 (C9), as an essential component of terminal membrane attack complex of complement system, plays an important role in innate immune defense. However, the function and regulatory mechanism of C9 in the antimicrobial immune response of teleost fish remain unclear. In this study, the open reading frame of Nile tilapia (Oreochromis niloticus) C9 (OnC9) gene was amplified. The mRNA and protein expression of OnC9 were significantly changed upon infection with Streptococcus agalactiae and Aeromonas hydrophila in vivo and in vitro. Upon bacterial challenge, the OnC9 knockdown could lead to rapid proliferation of the pathogenic bacteria, ultimately resulting in tilapia death. However, the phenotype was rescued by re-injection of OnC9, which restored the healthy status of the knockdown tilapia. Further, the OnC9 was an essential component in complement-mediated cell lysis and associated with OnCD59 to regulate the efficiency of lysis. Overall, this study indicates that OnC9 is involved in host defense against bacterial infection, and provides a valuable reference for further exploration of the molecular regulatory mechanism of C9 in innate immune defense in a primary animal.

Functional Divergence of the N-Lobe and C-Lobe of Transferrin Gene in Pungitius sinensis (Amur Stickleback)

Transferrin is an important iron-binding glycosylated protein and plays key roles in iron-binding and immune response. Here, a 2037-bp open reading frame was obtained from our previous transcriptome sequencing data of Amur stickleback, which encoded a 679 amino acid putative transferrin protein harbored obvious N-lobe and C-lobe domains. The tissue-specific expression pattern showed that the transcript was detected in a variety of tissues, with the highest signal in liver. Moreover, Streptococcus iniae pathogen stimulation can increase the expression level of this transcript, implying important immune properties for organisms. Next, N-lobes and C-lobes were obtained from 45 fish species. The phylogenetic tree showed that N-lobes and C-lobes were in two different evolutionary branches, and they had different motif composition. Functional divergence indicated a higher evolutionary rate or site-specific alteration among the N-lobe and C-lobe groups. Ka/Ks value of C-lobe group was relatively higher than that of N-lobe group, indicating a faster change rate of C-lobe sequences in evolution. Moreover, some sites experiencing positive selection were also found, which may be involved in the iron- or anion-binding, pathogen resistance and diversification of transferrin protein. Differential iron-binding activity was also detected between N-lobe and C-lobe of Amur stickleback transferrin protein with Chrome Azurol S assay. Compared with the C-lobe, the N-lobe showed stronger growth inhibitory activity of Escherichia coli, implying their potential antibacterial properties. This study will give a reference for subsequent research of transferrin proteins.

Antagonism of cysteinyl leukotriene receptors by zafirlukast modulated acute inflammatory reaction in tilapia, Oreochromis niloticus

To identify activation pathways and effector mechanisms of innate immunity in fish has become relevant for the sanitary management of intensive fish farming. However, little is known about the blocking of cysteinyl leukotrienes receptors (CysLTRs) and their effects in teleost fish. Our study evaluated the anti-inflammatory effect of 250 and 500 μg zafirlukast (antagonist of CysLTRs)/kg b.w., administered orally in the diet, during acute inflammatory reaction induced by Aeromonas hydrophila bacterins in Oreochromis niloticus. 80 tilapia were distributed in 10 aquariums (100L of water each, n = 8) to constitute three treatments: Control (inoculated with A. hydrophila bacterin and untreated); Treated with 250 μg or 500 μg of zafirlukast/kg b.w. and inoculated. To be evaluated in three periods: 6, 24 and 48 h post-inoculation (HPI), totaling nine aquariums. A tenth group was sampled without any stimulus to constitute reference values (Physiological standards). Tilapia treated with zafirlukast demonstrated dose-response effect in the decrease of accumulated inflammatory cells, strongly influenced by granulocytes and macrophages. Zafirlukast treated-tilapia showed decrease in blood leukocyte counts (mainly neutrophils, and monocytes) and reactive oxygen species production. Treatment with zafirlukast resulted in down-regulation of ceruloplasmin, complement 3, alpha2-macroglobulin, transferrin and apolipoprotein A1, as well as up-regulation of haptoglobin. Our study provided convincing results in the pathophysiology of tilapia inflammatory reaction, considering that treatment with zafirlukast, antagonist of cysteinyl leukotriene receptors, resulted in a dose-response effect by suppressing the dynamics between leukocytes in the bloodstream and cell accumulation in the inflamed focus, as well as modulated the leukocyte oxidative burst and the acute phase protein response.

Composition of uterine milk and its changes with gestational period in red stingrays (Hemitrygon akajei)

Uterine milk is secreted in the uterus for embryo nutrition in several elasmobranch species and may contribute to rapid embryonic growth, but the details of its composition and its functions are poorly understood. In this study, to explore the roles of uterine milk for embryos, its components throughout the gestational period were analysed in detail. Uterine milk was collected from pregnant red stingrays (Hemitrygon akajei) in the early, middle and late gestational periods, respectively (n= 3 for each period). The crude composition, constituent proteins and fatty acids in the milk were analysed. The uterine milk was rich in proteins throughout the gestational period, whereas lipids dramatically increased in the middle period and reduced slightly towards the late period. Some proteins potentially associated with nutrition, cartilage growth and embryonic immunity were found. Several enzymes related to central metabolism were also detected. The constituent fatty acids in the middle and late periods were similar to those in the egg yolks of elasmobranchs, except for C18:2, which was rich only in the uterine milk. The most abundant fatty acid in the milk was C16:1, which could function as a lipokine to promote lipid metabolism in the embryo. This study's data suggest that uterine milk may be secreted in addition to the egg yolk in elasmobranchs to support rapid and healthy embryonic growth.

Enhancement of immune proteins expression in skin mucus of Japanese flounder Paralicthys olivaceus upon feeding a diet supplemented with high concentration of ascorbic acid

To search immune defense proteins in skin mucus of Japanese flounder fed with a diet containing high concentration of ascorbic acid, we carried out 2D-PAGE and compared the resolved pattern of proteins between control group that fed commercial diet and ascorbic acid supplemented group (AsA group) fed a diet supplemented with high concentration of ascorbic acid (2,000 mg/kg) for 7 days. The results revealed that there were many proteins exhibited distinct increase in AsA group. Among them, 6 regions that showed a dramatic elevation were chosen for protein identification using LC-MS/MS analysis and Mascot database search. Six proteins were identified, i.e. serotransferrin (Sero), transferrin (Trans), warm temperature acclimation-related 65 kDa protein (Wap65), complement component c3 (C3), hemoglobin beta-A chain (Hbß) and apolipoprotein A-1 (Apo). Quantitative RT-PCR analysis showed that the mRNA level of Hbß in epidermis of AsA group gave much higher increase (11.6 folds) than control group; the levels of Sero/Trans, Wap65, C3 and Apo showed no apparent difference between the two groups. The mRNA levels of wap65 and c3 in the liver and Apo in the kidney of AsA group exhibited significant increase in comparison to control group. In the case of secreted immunoglobulin M (IgM) and lysozyme (lyz), no difference of the mRNA levels of IgM in epidermis, gill, kidney, spleen and intestine, and lyz in epidermis, gill, spleen and intestine, was observed. The results of in situ hybridization confirmed the elevation of Hbß mRNA level in the epidermis tissue of AsA group. Our present study provided additional evidence showing the effectiveness of AsA in activating innate immune defense system in skin mucosal tissue of fish.

Identification and functional characterization of the transcription factor coding Dp1 gene in large yellow croaker Pseudosciaena crocea

The transcription factor Dp1, as a binding partner, often forms a dimerization complex with typical E2F to play a central role in regulating gene expression during G1/S cell cycle progression. In this study, a full-length dp1 cDNA (Pcdp1) was successfully cloned and characterized from the large yellow croaker Pseudosciaena crocea. The nucleotidic sequence of Pcdp1 is 1,427 bp long with an open reading frame (ORF) of 1,239 bp encoding a putative protein of 412 amino acids, a 5′-untranslated region of 116 bp and a 3′-untranslated region of 70 bp. Prediction of protein domains showed that PcDp1 contains a DNA-binding domain (DBD) with a DEF box, a dimerization domain and an acidic region at C terminus with transcription activity. Homology comparisons indicated that PcDp1 shared the highest sequence identity of 98.55% with Oreochromis niloticus dp1, followed by 88.72% identity with Danio rerio dp1 and a relatively low identity of 78.91–80.55% with its mammalian and amphibian counterparts. The mRNA of Pcdp1 showed ubiquitously expression in all analyzed tissues, with the highest level of expression in the body kidney. Moderate expression levels of Pcdp1 was found in several immune-related tissues including the gills, head kidney and liver, indicating that PcDp1 might play an important role in osmotic pressure regulation and immune response of the large yellow croaker. The subcellular localization of PcDp1 revealed that it is mainly distributed in the cytoplasm both in COS-7 and parenchymal cells of the spleen, head kidney and kidney tissues. Furthermore, the recombinant PcDp1 exhibited DNA-binding activity to E2F site in vitro. In conclusion, these results indicated that PcDp1 may participate in immune regulation and provide a foundation for further study of the regulatory mechanism of Dp1 in teleosts.

Mannose-Binding Lectin Possesses Agglutination Activity and Promotes Opsonophagocytosis of Macrophages with Calreticulin Interaction in an Early Vertebrate

The innate immune system is an ancient defense system in the process of biological evolution, which can quickly and efficiently resist pathogen infection. In mammals, mannose-binding lectin (MBL) is a key molecule in the innate immune and plays an essential role in the first line of host defense against pathogenic bacteria. However, the evolutionary origins and ancient roles of immune defense of MBL and its mechanism in clearance of microbial pathogens are still unclear, especially in early vertebrates. In this study, Oreochromis niloticus MBL (OnMBL) was successfully isolated and purified from the serum of Nile tilapia (O. niloticus). The OnMBL was able to bind and agglutinate with two important pathogens of tilapia, Streptococcus agalactiae and Aeromonas hydrophila Interestingly, the OnMBL was able to significantly inhibit the proliferation of pathogenic bacteria and reduce the inflammatory response. Upon bacterial challenge, the downregulation of OnMBL expression by RNA interference could lead to rapid proliferation of the pathogenic bacteria, ultimately resulting in tilapia death. However, the phenotype was rescued by reinjection of the OnMBL, which restored the healthy status of the knockdown tilapia. Moreover, a mechanistic analysis revealed that the OnMBL could clear pathogenic bacteria by collaborating with cell-surface calreticulin to facilitate phagocytosis in a complement activation-independent manner. To our knowledge, these results provide the first evidence on the antibacterial response mechanism of MBL performing evolutionary conserved function to promote opsonophagocytosis of macrophages in early vertebrates and reveals new insights into the understanding of the evolutionary origins and ancient roles basis of the C-type lectins in the innate immune defense.

Early-life infection with a bacterial pathogen increases expression levels of innate immunity related genes during adulthood in zebrafish

Early-life exposure to different stressors can lead to various consequences on fish health status in later life development. To evaluate the effects of Aeromonas salmonicida achromogenes infection in the early-life on immunity in adulthood, zebrafish were either early-infected at 18 days post-fertilization (dpf), chronically infected from 18 to 35 dpf, or late infected at 35 dpf and then grown up to 61 dpf to be re-infected with the pathogen. The age of first infection was shown to influence both, level and timing of the immune gene expressions, especially for inflammation-related genes. In addition, evidence for an innate immune memory in zebrafish primarily infected with the pathogen at 35 dpf and re-infected at 61dpf provide new insights to consolidate the concept of a "trained" innate immunity in fish.

Large-scale profiling of the proteome and dual transcriptome in Nile tilapia (Oreochromis niloticus) challenged with low- and high-virulence strains of Streptococcus agalactiae

Streptococcus agalactiae is a common pathogen in aquatic animals, especially tilapia, that hinders aquaculture development and leads to serious economic losses. Previously, a S. agalactiae strain named HN016 was identified from infected tilapia, and the attenuated strain YM001 was subsequently obtained by continuous passaging in Tryptic Soy Broth (TSB) medium. YM001 has been demonstrated as a safe vaccine for S. agalactiae infection in tilapia. To understand the molecular bases of the virulence of these two strains, we performed proteomic and transcriptomic analysis to reveal the protein and gene expression changes in the liver and intestine during the infection process. HN016 significantly decreased the contents of white blood cells (WBCs), neutrophils (NEUs), red blood cells (RBCs) and hematocrit (HCT) and increased the levels of total protein (TP), albumin (ALB) and globulin (GLO), while no such significant differences were observed when comparing the control with YM001. During the infection process, pathogenic peptidoglycan hydrolase, CSPA and membrane proteins were significantly differentially expressed between YM001 and HN016. Furthermore, both proteome and transcriptome data showed that the complement and coagulation cascades pathway and the antigen processing and presentation pathway were stimulated in the liver and intestine, respectively, by YM001 infection compared to HN016 infection. The interaction network analysis of key virulence genes from pathogens suggested that CSPA, as a key node, affects the expression of DOLPP1, MIPEP, PA2G4, OCIAD1, G3BP1 and CLIC5 with a positive correlation. The present evidence suggests that during the infection process, CSPA was the key genes contributing to low virulence in YM001.

Expression and functional analysis of Nile tilapia transferrin receptors (TfRs) in host resistance to pathogenic bacteria and iron ion metabolism

Transferrin receptors (TfRs) play an essential role in iron-withholding strategy, and are involved in immune response against bacterial infection. In this study, the transferrin receptor 1 (OnTfR1) and transferrin receptor 2 (OnTfR2) genes are identified and characterized in Nile tilapia (Oreochromis niloticus). The open reading frames of OnTfR1 and OnTfR2 are 2220 and 2343 bp of nucleotide sequence, encoding 739 and 780 amino acids, respectively. The deduced proteins of OnTfR1 and OnTfR2 are highly homologous to those of other species, containing three conserved TfR superfamily domains (PA TfR domain, M28 TfR domain and TfR dimer domain). Expression analyses of OnTfRs in the healthy tilapia reveal that the OnTfR1 and OnTfR2 transcripts are the most abundant in the liver. The in vivo studies show that the expressions of OnTfRs are significantly up-regulate in liver and spleen, following infections of Streptococcus agalactiae and Aeromonas hydrophila. In addition, the in vitro studies reveal that the up-regulations of OnTfR expressions are also significant in monocytes/macrophages and hepatocytes upon the stimulations of S. agalactiae and A. hydrophila. Moreover, the iron ion (Fe³⁺) could significantly increase the expressions of OnTfRs in monocytes/macrophages and hepatocytes. Taken together, the present study indicates that OnTfRs may be involved in host defense against bacterial infection and possess the function of combining or transporting iron ions in Nile tilapia.

Screening for protective antigens of Cyprinid herpesvirus 2 and construction of DNA vaccines

BACKGROUND

In recent years, crucian carp hematopoietic necrosis caused by Cyprinid herpesvirus 2 (CyHV-2) infection has caused an enormous economic loss to the aquaculture industry.

METHODS

In this study antigenic epitope analysis was performed on the membrane proteins of CyHV-2, and 8 antigen-rich peptide fragments were selected for prokaryotic expression. Then, the immunogenicity of the recombinant proteins was analyzed. On this basis, DNA vaccines were constructed for immunization of hybridized Prussian carps. The protective effect of DNA vaccines against challenge in hybridized Prussian carps was evaluated.

RESULTS

The results showed that all 8 recombinant proteins were successfully expressed. Among the recombinant proteins, ORF16, tORF25, tORF64, and ORF146, gave a positive serum reaction with CyHV-2. Of the four proteins used for the immunization of silver crucian carps, the antibody titer induced by tORF25 was the highest. The DNA vaccine, pEGFP-N1-ORF25, was constructed based on ORF25 and able to induce production of specific antibodies in carps, while up-regulating the expression of MHCⅠ, IL-1β, C3, and TF-A in the kidneys of carps. Moreover, the immunoprotective rate was increased to 70% in hybridized Prussian carps.

CONCLUSION

The results showed that the DNA vaccine constructed based on the ORF25 gene had a greater immune protective effect and can be used as a candidate vaccine for immunoprotection against CyHV-2.