Cloning and characterization of a TNF-like protein of Plecoglossus altivelis (ayu fish)

Toll-like Receptor Expression in Pelodiscus sinensis Reveals Differential Responses after Aeromonas hydrophila Infection

Background: Toll-like receptor (TLR), as an important pattern recognition receptor, is a bridge between non-specific immunity and specific immunity, and plays a vital role in the disease resistance of aquatic animals. However, the function of TLR in Pelodiscus sinensis is still unclear. Methods and Results: The sequence characteristics and homology of three TLRs (PsTLR2, PsTLR3 and PsTLR5) were determined in this investigation. Their annotation and orthologies were supported by phylogenetic analysis, functional domain prediction, and sequence similarity analysis. qPCR showed that the identified TLRs were expressed in all tissues, among the high expression of PsTLR5 in the brain and liver and the high expression of PsTLR2 and PsTLR3 in the liver. PsTLR2 mRNA expression increased 6.7-fold in the liver 12 h after Aeromonas hydrophila infection, while the mRNA expression of PsTLR3 was down-regulated by 0.29 times in liver and 0.31 times in spleen. The mRNA expression of PsTLR5 was significantly up-regulated in four immune tissues, and it was up-regulated by 122.8 times in the spleen after 72 h infection. Finally, the recombinant proteins of extracellular LRR domains of these three TLRs were obtained by prokaryotic expression technology, and the binding tests were performed to discover their ability of binding pathogenic microorganisms. Microbial binding test showed that rPsTLR2, rPsTLR3 and rPsTLR5 can combine A. hydrophila, Edwardsiella tarda, Vibrio parahaemolyticus, Staphylococcus aureus, Streptococcus agalactiae and Candida albicans, while rPsTLR3 can bind A. hydrophila, E. tarda, V. parahaemolyticus and C. albicans. Conclusions: Our findings suggested that TLRs may be crucial to turtles' innate immune response against microbes.

Modulatory effects of necroptosis: A potential preventive approach to control diseases in fish

Necroptosis is a caspase-independent programmed cell death process characterized by morphological similarities to necrosis and the potential to cause significant inflammatory reactions. The initiation, execution, and inhibition of necroptosis involve a complex interplay of various signaling proteins. When death receptors bind to ligands, necroptosis is triggered through the receptor-interacting serine/threonine-protein kinase 1 (RIPK1)/RIPK3/Mixed Lineage Kinase Domain-Like (MLKL) axis, leading to inflammatory reactions in the surrounding tissues. This process encompasses numerous physiological regulatory mechanisms and contributes to the development and progression of certain diseases. The mechanisms of necroptosis were not well conserved across terrestrial and aquatic organisms, with differences in some components and functions. Given the significant challenges that aquatic animal diseases pose to aquaculture, research interest in necroptosis has surged recently, particularly in studies focusing on fish. Understanding necroptosis in fish can lead to interventions that offer potential breakthroughs in disease inhibition and fish health improvement.

Cytokine networks provide sufficient evidence for the differentiation of CD4+ T cells in teleost fish

Cytokines, a class of small molecular proteins with a wide range of biological activities, are secreted mainly by immune cells and function by binding to the corresponding receptors to regulate cell growth, differentiation and effects. CD4⁺ T cells can be defined into different lineages based on the unique set of signature cytokines and transcription factors, including helper T cells (Th1, Th2, Th17) and regulatory T cells (Treg). In teleost, CD4⁺ T cells have been identified in a variety of fish species, thought to play roles as Th cells, and shown to be involved in the immune response following specific antigen stimulation. With the update of sequencing technologies, a variety of cytokines and transcription factors capable of characterizing CD4⁺ T cell subsets also have been described in fish, including hallmark cytokines such as IFN-γ, TNF-α, IL-4, IL-17, IL-10, TGF-β and unique transcription factors such as T-bet, GATA3, RORγt, and Foxp3. Hence, there is increasing evidence that the subpopulation of Th and Treg cells present in mammals may also exist in teleost fish. However, the differentiation, plasticity and precise roles of Th cell subsets in mammals remain controversial. Research on the identification and differentiation of fish Th cells is still in its infancy and requires more significant effort. Here we will review recent research advances in characterizing the differentiation of fish CD4⁺ T cells by cytokines and transcription factors, mainly including the identification of Th and Treg cell hallmark cytokines and transcription factors, the regulatory role of cytokines on Th cell differentiation, and the function of Th and Treg cells in the immune response. The primary purpose of this review is to deepen our understanding of cytokine networks in characterizing the differentiation of CD4⁺ T cells in teleost.

Molecular characterization, expression analysis and function identification of TNFα in black rockfish (Sebastes schlegelii)

TNFα, as a pro-inflammatory cytokine, plays an important role in inflammation and immune homeostasis maintaining. However, the knowledge about the immune functions of teleost TNFα against bacterial infections is still limited. In this study, the TNFα was characterized from black rockfish (Sebastes schlegelii). The bioinformatics analyses showed the evolutionary conservations in sequence and structure. The expression levels of Ss_TNFα mRNA were significantly up-regulated in the spleen and intestine after Aeromonas salmonicides and Edwardsiella tarda infections, and dramatically down-regulated in PBLs after LPS and poly I:C stimulations. Meanwhile, the extremely up-regulated expressions of other inflammatory cytokines (especially for IL-1β and IL17C) were observed in the intestine and spleen after bacterial infection and down-regulations were obtained in PBLs. The significant regulation with expression patterns of Ss_TNFα and other inflammatory cytokine mRNAs illustrated the variations of immunity in different tissues and cells of black rockfish. The regulated functions of Ss_TNFα in the up/downstream signaling pathways were preliminarily verified on the transcription and translation levels. Subsequently, in vitro knockdown of Ss_TNFα in the intestine cells of black rockfish confirmed the important immune roles of Ss_TNFα. Finally, the apoptotic analyses were conducted in PBLs and intestine cells of black rockfish. The rapid increases of the apoptotic rates were obtained in both PBLs and intestine cells after treatment with rSs_TNFα, but distinct apoptotic rates at the early and late stages of apoptosis were observed between these two types of cells. The results of apoptotic analyses suggested that Ss_TNFα could trigger apoptosis of different cells in different strategies in black rockfish. Overall, the findings in this study indicated the important roles of Ss_TNFα in the immune system of black rockfish during pathogenic infection, as well as the potential function on biomarker for monitoring the health status.

Recent advances in the crosstalk between adipose, muscle and bone tissues in fish

Control of tissue metabolism and growth involves interactions between organs, tissues, and cell types, mediated by cytokines or direct communication through cellular exchanges. Indeed, over the past decades, many peptides produced by adipose tissue, skeletal muscle and bone named adipokines, myokines and osteokines respectively, have been identified in mammals playing key roles in organ/tissue development and function. Some of them are released into the circulation acting as classical hormones, but they can also act locally showing autocrine/paracrine effects. In recent years, some of these cytokines have been identified in fish models of biomedical or agronomic interest. In this review, we will present their state of the art focusing on local actions and inter-tissue effects. Adipokines reported in fish adipocytes include adiponectin and leptin among others. We will focus on their structure characteristics, gene expression, receptors, and effects, in the adipose tissue itself, mainly regulating cell differentiation and metabolism, but in muscle and bone as target tissues too. Moreover, lipid metabolites, named lipokines, can also act as signaling molecules regulating metabolic homeostasis. Regarding myokines, the best documented in fish are myostatin and the insulin-like growth factors. This review summarizes their characteristics at a molecular level, and describes both, autocrine effects and interactions with adipose tissue and bone. Nonetheless, our understanding of the functions and mechanisms of action of many of these cytokines is still largely incomplete in fish, especially concerning osteokines (i.e., osteocalcin), whose potential cross talking roles remain to be elucidated. Furthermore, by using selective breeding or genetic tools, the formation of a specific tissue can be altered, highlighting the consequences on other tissues, and allowing the identification of communication signals. The specific effects of identified cytokines validated through in vitro models or in vivo trials will be described. Moreover, future scientific fronts (i.e., exosomes) and tools (i.e., co-cultures, organoids) for a better understanding of inter-organ crosstalk in fish will also be presented. As a final consideration, further identification of molecules involved in inter-tissue communication will open new avenues of knowledge in the control of fish homeostasis, as well as possible strategies to be applied in aquaculture or biomedicine.

Epitope screening of the major capsid protein within grouper iridovirus of Taiwan and the immunoprotective effect with SWCNTs as the vaccine carrier

Iridovirus can cause a mass of death in grouper, leading to huge economic loss in recent years. At present, practical vaccine is still the best way to control the outbreak of this virus. Many researches had indicated that the major capsid protein (MCP) of grouper iridovirus of Taiwan (TGIV) is an effective antigen to induce a specific immune response in grouper. However, these traditional vaccines that based on large proteins or whole organisms are faced with challenges because of the unnecessary antigenic load. Thus, in this study, we screened the dominant linear epitope within the MCP of TGIV and then, a new peptide vaccine (P2) was developed via prokaryotic expression system. Furthermore, SWCNTs was used as a vaccine carrier to enhance the immunoprotective effect. To evaluate the immunoprotective effect of this vaccine, a total of 245 fish were vaccinated with P2 (5, 10, 20 mg L^-1) and SWCNTs-P2 (5, 10, 20 mg L^-1) via immersion before being challenged with live TGIV at 28 days post immunization (d.p.i.). Results showed that the serum antibody titer, enzymatic activity, expression level of some immune-related genes (CC chemokine, IgM and TNF-α) and survival rate were significantly increased (SWCNTs-P2, 20 mg L^-1, 100%) compared to the control group (0%). These results indicated that this peptide vaccine could effectively induce specific immune response in vaccinated groupers. Functionalized SWCNTs could serve as a carrier of the peptide vaccine to enhance the immunoprotective effect via immersion. To sum up, epitope screening might be a potential way to develop an effective vaccine nowadays, and SWCNTs might provide a practical method that can be used in large-scale vaccination, especially for juvenile fish, to fight against diseases in aquaculture industry.

The unique structure of the zebrafish TNF-α homotrimer

In the current study, zebrafish TNF-α1 (zTNF-α1) was crystallized, and the structure was analyzed. The zTNF-α1 trimer is composed of three monomers whose height and width are 50 Å and 60 Å, respectively. Compared with human TNF-α, zTNF-α1 shows only ~30% amino acid identity, the EF loop of each monomer lacks three amino acids, the CD loop is increased by four amino acids, and the AA'' loop is increased by one amino acid. In addition, an A″-β-chain is added to the zTNF-α1 monomer, forming two β-sheet layers with 6:5 β-chains. The top of the trimer is missing three amino acids and the inner coil because the EF loop seals the central hole at the top, forming a unique structure. In conclusion, the results elucidated the structure of the zTNF-α1 trimer, providing immunological knowledge for studying TNF-α function in the zebrafish animal model and structural information for exploring TNF-α family evolution.

Molecular characterization, expression analysis and function identification of Pf_TNF-α and its two receptors Pf_TNFR1 and Pf_TNFR2 in yellow catfish (Pelteobagrus fulvidraco)

Inflammation is a common manifestation of body immunity and mediates a cascade of cytokines. Tumor necrosis factor-α (TNF-α), as a multi-effect cytokine, plays an important role in the inflammatory response by interacting with its receptor (TNFR). In this study, Pf_TNF-α, Pf_TNFR1 and Pf_TNFR2 genes were cloned from yellow catfish (Pelteobagrus fulvidraco), and bioinformatics analyses showed that the three genes were conserved and possessed similar sequence characteristics as those of other vertebrates. The qPCR results showed that Pf_TNF-α, Pf_TNFR1 and Pf_TNFR2 mRNAs were constitutively expressed in 14 tissues and the lymphocytes of four tissues from healthy adults. The mRNA expression levels of Pf_TNF-α and Pf_TNFR1 genes were significantly up-regulated in the spleen, liver, trunk kidney, head kidney and gill after Edwardsiella ictaluri infection, while the mRNA expression of Pf_TNFR2 was significantly up-regulated in the spleen, and down-regulated in the liver and gill. In the isolated peripheral blood leukocytes (PBLs) of yellow catfish, the expression of Pf_TNF-α mRNA was notably up-regulated and the two Pf_TNFR transcripts were distinctly down-regulated after stimulation with lipopolysaccharides (LPS), peptidoglycan (PGN), polyinosinic-polycytidylic acid (Poly I:C) and phytohaemagglutinin (PHA). After stimulated by recombinant (r) Pf_sTNF protein, the mRNA expressions of various inflammatory factors genes were up-regulated in the PBLs. Meanwhile, rPf_sTNF promoted the phagocytic activity of leukocytes, whereas the activity mediated by rPf_sTNF could be inhibited by rPf_TNFR1CRD2/3 and rPf_TNFR2CRD2/3. The up-regulation of TNF-α and IL-1β mRNAs expression triggered by rPf_sTNF could be inhibited by MAPK inhibitor (VX-702) and NF-κB inhibitor (PDTC). rPf_sTNF induced the expression of FADD mRNA in PBLs and increased the apoptotic rate of PBLs, and inhibiting the NF-κB and MAPK signal pathways could enhance the apoptosis of PBLs. The results indicate that Pf_TNF-α, Pf_TNFR1 and Pf_TNFR2 play important roles in the immune response of yellow catfish to bacterial invasion.

The involvement of TNF-α and TNF-β as proinflammatory cytokines in lymphocyte-mediated adaptive immunity of Nile tilapia by initiating apoptosis

Tumor necrosis factors (TNFs) are pleiotropic cytokines with important functions in homeostasis and disease pathogenesis. Recent advances have shown that TNFs are also involved in the regulation of adaptive immune responses. However, the knowledge about how TNF participates in and regulates adaptive immune response in early vertebrates is still limited. In present study, we identified two isoforms of TNF, TNF-α and TNF-β, from Nile tilapia Oreochromis niloticus (On-TNF-α and β). After analyzing the sequence characteristics, we investigated their regulatory roles in adaptive immune response of this fish species. On-TNF-α and β are evolutionarily conserved compare with their homologs from other vertebrates. Both TNFs were distributed in a wide range of tissues in O. niloticus, and with relative higher expression level in gill. After the animals were infected by Streptococcus agalactiae, mRNA levels of On-TNF-α and TNF-β in spleen lymphocytes were significantly upregulated during the primary response stage of adaptive immunity. Meanwhile, both TNF proteins in spleen lymphocytes were also dramatically elevated during the adaptive immune stage after bacterial infection. These results indicate the potential participation of On-TNF-α and TNF-β in adaptive immune response of Nile tilapia. Furthermore, On-TNF-α and β transcripts were obviously augmented, once spleen lymphocytes were activated by T cell-specific mitogen PHA. More importantly, both recombinant On-TNF-α and β could induce the apoptosis of head-kidney leukocytes of Nile tilapia. And On-TNF-β but not On-TNF-α promoted the apoptosis by activating caspase-8 in the target cells. Altogether, our study revealed that TNF-α and TNF-β participated in the lymphocyte-mediated adaptive immune response of Nile tilapia by initiating the apoptosis, and thus shed novel perspective for the regulatory mechanism of adaptive immunity in teleost.

Functions of TNF-α1 and TNF-α2 in large yellow croaker (Larimichthys crocea) in monocyte/macrophage activation

Tumor necrosis factor-α (TNF-α) plays crucial roles in cell development, proliferation, apoptosis, inflammation, and immunity. TNF-α genes have been identified in various fish species, however, their biological functions remain to be further clarified. In this study, we identified a novel TNF-α homologue (LcTNF-α2) from large yellow croaker (Larimichthys crocea), which shares a low amino acid sequence identity to the previously reported large yellow croaker TNF-α (LcTNF-α1). The open reading frame of LcTNF-α2 is 714 nucleotides long, encoding a peptide of 237 amino acids (aa). The deduced LcTNF-α2 protein contains a 23-aa transmembrane region, a TACE restriction site at residues T71/L72, a TNF family signature (I108- F135), and two conserved cysteine residues (C39 and C179), as found in other known TNF-α sequences. Both LcTNF-α1 and LcTNF-α2 genes were constitutively expressed in all examined tissues and significantly up-regulated in the spleen and head kidney by Vibrio alginolyticus. Their transcripts were also detected in primary head kidney monocytes/macrophages (MO/Mϕs), lymphocytes (PKLs), granulocytes (PKGs), and large yellow croaker head kidney (LYCK) cell line and significantly increased in these cell types by inactivated Vibrio alginolyticus. Recombinant LcTNF-α1 and LcTNF-α2 proteins (rLcTNF-α1 and rLcTNF-α2) produced in Pichia pastoris not only significantly increased the production of reactive oxygen species (ROS), but also promoted the expression of proinflammatory cytokines (IL-1β, IL-6,IL-8, and TNF-α1) in MO/Mϕs from large yellow croaker. Even more, after stimulation with rLcTNF-α1 and rLcTNF-α2, the production of nitrogen oxide (NO) and the expression of inducible NO synthase (iNOS) gene were significantly up-regulated. However, only rLcTNF-α1 remarkedly enhanced the phagocytosis of MO/Mϕs and increased the expression of TNF-α2 in MO/Mϕs. These results therefore indicated that LcTNF-α1 and LcTNF-α2 both play roles in promoting activation of head kidney MO/Mϕs.

The proinflammatory cytokines TNF-α and IL-6 in lumpfish (Cyclopterus lumpus L.) -identification, molecular characterization, phylogeny and gene expression analyses

The proinflammatory cytokines TNF-α and IL-6 are important mediators of inflammatory reactions and orchestrators of the immune system in vertebrate. In this study, we have identified TNF-α and IL-6 in lumpfish, molecular characterized them at mRNA and gene level, performed homology modelling and measured their gene expression in different tissues and upon in vitro stimulation. A comprehensive phylogenetic analysis of TNF-α teleost sequences give novel insight into the TNF -α biology. Interestingly, we identified two isoforms of luIL-6. In normal tissue and leukocyte, the level of luTNF-α transcripts was higher than luIL-6. The expression pattern were parallel, except for brain, eye and gonad, and they displayed a similar induction pattern upon exposure to PAMPs, being most highly upregulated by flagellin. This is the first in-depth characterization of TNF and IL-6 in lumpfish. In recent years, lumpfish has become an important species for the aquaculture industry and establishment of qPCR-assays of luTNF-α and luIL-6 provide a valuable tool to measure effect of immune modulation, such as vaccination, microbiological disease and physiological trials. Lumpfish is also interesting for comparative studies as it represent a phylogenetic group that is poorly described immunologically.

Mechanisms of Fish Macrophage Antimicrobial Immunity

Overcrowding conditions and temperatures shifts regularly manifest in large-scale infections of farmed fish, resulting in economic losses for the global aquaculture industries. Increased understanding of the functional mechanisms of fish antimicrobial host defenses is an important step forward in prevention of pathogen-induced morbidity and mortality in aquaculture setting. Like other vertebrates, macrophage-lineage cells are integral to fish immune responses and for this reason, much of the recent fish immunology research has focused on fish macrophage biology. These studies have revealed notable similarities as well as striking differences in the molecular strategies by which fish and higher vertebrates control their respective macrophage polarization and functionality. In this review, we address the current understanding of the biological mechanisms of teleost macrophage functional heterogeneity and immunity, focusing on the key cytokine regulators that control fish macrophage development and their antimicrobial armamentarium.

Identification and expression analysis of two pro-inflammatory cytokines, TNF-α and IL-8, in cobia (Rachycentron canadum L.) in response to Streptococcus dysgalactiae infection

Tumor necrosis factor-alpha (TNF-α) and interleukin-8 (IL-8/CXCL8) play pivotal roles in mediating inflammatory responses to invading pathogens. In this study, we identified and analyzed expressions of cobia TNF-α and IL-8 during Streptococcus dysgalactiae infection. The cloned cDNA transcript of cobia TNF-α comprised of 1281 base pairs (bp), with a 774 bp open reading frame (ORF) encoding 257 amino acids. The deduced amino acid sequence of cobia TNF-α showed a close relationship (84% similarity) with TNF-α of yellowtail amberjack. The cloned IL-8 cDNA sequence was 828 bp long, including a 300-bp ORF encoding 99 amino acids. The deduced amino acid sequence of cobia IL-8 shared 90% identity with IL-8 of striped trumpeter. Cobia challenged with a virulent S. dysgalactiae strain displayed an early significant up-regulation of TNF-α and IL-8 in head kidney, liver, and spleen. Notably, IL-8 expression level increased dramatically in the liver at the severe stage of infection (72 h). In conclusion, a better understanding of TNF-α and IL-8 allows more detailed investigation of immune responses in cobia and furthers study on controlling the infectious disease caused by S. dysgalactiae.

The Function of Fish Cytokines

What is known about the biological activity of fish cytokines is reviewed. Most of the functional studies performed to date have been in teleost fish, and have focused on the induced effects of cytokine recombinant proteins, or have used loss- and gain-of-function experiments in zebrafish. Such studies begin to tell us about the role of these molecules in the regulation of fish immune responses and whether they are similar or divergent to the well-characterised functions of mammalian cytokines. This knowledge will aid our ability to determine and modulate the pathways leading to protective immunity, to improve fish health in aquaculture.

Molecular characterization and expression analysis of the first Porifera tumor necrosis factor superfamily member and of its putative receptor in the marine sponge Chondrosia reniformis

Here we report the molecular cloning and characterization of the first Tumor Necrosis Factor homologous and of its putative receptor in the marine sponge Chondrosia reniformis: chTNF and chTNFR, respectively. The deduced chTNF amino acid sequence is a type II transmembrane protein containing the typical TNFSF domain. Phylogenetic analysis reveals that chTNF is more related to Chordata TNFs rather than to other invertebrates. chTNF and chTNFR are constitutively expressed both in the ectosome and in the choanosome of the sponge, with higher levels in the ectosome. chTNF and chTNFR mRNAs were monitored in sponge fragmorphs treated with Gram(+) or Gram(-) bacteria. chTNF was significantly upregulated in Gram(+)-treated fragmorphs as compared to controls, while chTNFR was upregulated by both treatments. Finally, the possible chTNF fibrogenic role in sponge fragmorphs was studied by TNF inhibitor treatment measuring fibrillar and non fibrillar collagen gene expression; results indicate that the cytokine is involved in sponge collagen deposition and homeostasis.

CsTNF1, a teleost tumor necrosis factor that promotes antibacterial and antiviral immune defense in a manner that depends on the conserved receptor binding site

Tumor necrosis factor (TNF) is one of the most important cytokines involved in inflammation, apoptosis, cell proliferation, and stimulation of the immune system. The TNF gene has been cloned in teleost fish; however, the in vivo function of fish TNF is essentially unknown. In this study, we report the identification of a TNF homologue, CsTNF1, from tongue sole (Cynoglossus semilaevis) and analysis of its expression and biological effect. CsTNF1 is composed of 242 amino acid residues and possesses a TNF domain and conserved receptor binding sites. Expression of CsTNF1 was detected in a wide range of tissues and up-regulated in a time-dependent manner by experimental challenge with bacterial and viral pathogens. Bacterial infection of peripheral blood leukocytes (PBL) caused extracellular secretion of CsTNF1. Purified recombinant CsTNF1 (rCsTNF1) was able to bind to PBL and stimulate the respiratory burst activity of PBL. In contrast, rCsTNF1M1 and rCsTNF1M2, the mutant CsTNF1 bearing substitutions at the receptor binding site, failed to activate PBL. Fish administered with rCsTNF1, but not with rCsTNF1M1 and rCsTNF1M2, exhibited enhanced expression of IL-1, IL-6, IL-8, IL-27, TLR9 and G3BP in a time-dependent manner and augmented resistance against bacterial and viral infection. These results provide the first evidence that the receptor binding sites are essential to a fish TNF, and that CsTNF1 is involved in the innate immune defense of fish against microbial pathogens.

Expressed sequence tag analyses of three leukocyte subpopulations in ayu Plecoglossus altivelis altivelis, separated by monoclonal antibodies

Ayu Plecoglossus altivelis altivelis are one of the most economically important fish for freshwater aquaculture in Japan. We conducted expressed sequence tag analyses of three leukocyte subpopulations, thrombocytes, neutrophils, and B lymphocytes in ayu using a next generation sequencer. The sequencing and de novo assembly yielded 22,494, 22,733, and 16,505 contigs from the thrombocyte, neutrophil, and B lymphocyte cDNA libraries, respectively. Pathways involving endocytosis, phagosomes, and lysosomes, were found in all three cDNA libraries using pathway analysis. The thrombocyte cDNA library contained 2894 unique sequences, including CXC chemokine receptor 4 and MHC class II. Cytokine and cytokine receptor genes such as interleukin (IL)-1β, IL-8, IL-1 receptor (IL-1R), IL-8RA, and IL-8RB were found among the 3056 unique sequences of the neutrophil cDNA library. Typical B lymphocyte related genes such as B cell linker protein, immunoglobulin (Ig) M, IgD and transforming growth factor β were found in the 1590 unique sequences of the B lymphocyte cDNA library. In summary, a large number of immune-related genes were identified from the three leukocyte cDNA libraries. Our results represent a valuable sequence resource for understanding the immune system function in ayu.

Characterization of three pro-inflammatory cytokines, TNFα1, TNFα2 and IL-1β, in cage-reared Atlantic bluefin tuna Thunnus thynnus

Atlantic bluefin tuna (BFT) (Thunnus thynnus) is of great economic significance for world aquaculture and therefore it is necessary to ensure optimal and sustainable conditions for the farming of this species. Intensive culture of fish may be limited by infectious diseases that can impact on growth performance and cause heavy losses. However, to date there are no reports of cloning and expression analysis of any major immune genes of Atlantic BFT although some immune genes are known in other BFT species. Therefore the aim of this study was to characterize the first cytokine molecules in Atlantic BFT, through: 1) Isolation of full-length cDNA and gene sequences of TNFα1, TNFα2 and IL-1β, 2) comparison of these molecules to known sequences in other vertebrates, especially teleost fish, by multiple sequence alignment, phylogenetic tree analysis and homology modeling; 3) Quantification of in vivo expression of these cytokines in selected tissues in reared BFT over the duration of the farming process. The results indicated that these three cytokines could have value for monitoring Atlantic BFT health status. Curiously, the liver seemed to be an important site of cytokine production during poor health conditions in this species, perhaps reflecting its role as an important organ involved in fish defenses.

Presence of two tumor necrosis factor (tnf)-α homologs on different chromosomes of zebrafish (Danio rerio) and medaka (Oryzias latipes)

Two or more isoforms of several cytokines including tumor necrosis factors (tnfs) have been reported from teleost fish. Although zebrafish (Danio rerio) and medaka (Oryzias latipes) possess two tnf-α genes, their genomic location and existence are yet to be described and confirmed. Therefore, we conducted in silico identification, synteny analysis of tnf-α and tnf-n from both the fish with that of human TNF/lymphotoxin loci and their expression analysis in zebrafish. We identified two homologs of tnf-α (named as tnf-α1 and tnf-α2) and a tnf-n gene from zebrafish and medaka. Genomic location of these genes was found to be as: tnf-α1, and tnf-n and tnf-α2 genes on zebrafish chromosome 19 and 15 and medaka chromosome 11 and 16, respectively. Several features such as existence of TNF family signature, conservation of genes in TNF loci with human chromosome, phylogenetic clustering and amino acid similarity with other teleost TNFs confirmed their identity as tnf-α and tnf-n. There were a constitutive expression of all three genes in different tissues, and an increased expression of tnf-α1 and -α2 and a varied expression of tnf-n ligand in zebrafish head kidney cells induced with 20 μg mL(-1) LPS in vitro. Our results suggest the presence of two tnf-α homologs on different chromosomes of zebrafish and medaka and correlate this incidence arising from the fish whole genome duplication event.

Two types of TNF-α exist in teleost fish: phylogeny, expression, and bioactivity analysis of type-II TNF-α3 in rainbow trout Oncorhynchus mykiss

TNF-α is a cytokine involved in systemic inflammation and regulation of immune cells. It is produced chiefly by activated macrophages as a membrane or secreted form. In rainbow trout, two TNF-α molecules were described previously. In this article, we report a third TNF-α (TNF-α3) that has only low identities to known trout molecules. Phylogenetic tree and synteny analyses of trout and other fish species suggest that two types (named I and II) of TNF-α exist in teleost fish. The fish type-II TNF-α has a short stalk that may impact on its enzymatic release or restrict it to a membrane-bound form. The constitutive expression of trout TNF-α3 was generally lower than the other two genes in tissues and cell lines, with the exception of the macrophage RTS-11 cell line, in which expression was higher. Expression of all three TNF-α isoforms could be modulated by crude LPS, peptidoglycan, polyinosinic:polycytidylic acid, and rIFN-γ in cell lines and primary macrophages, as well as by bacterial and viral infections. TNF-α3 is the most responsive gene at early time points post-LPS stimulation and can be highly induced by the T cell-stimulant PHA, suggesting it is a particularly important TNF-α isoform. rTNF-α3 produced in CHO cells was bioactive in different cell lines and primary macrophages. In the latter, it induced the expression of proinflammatory cytokines (IL-1β, IL-6, IL-8, IL-17C, and TNF-αs), negative regulators (SOCS1-3, TGF-β1b), antimicrobial peptides (cathelicidin-1 and hepcidin), and the macrophage growth factor IL-34, verifying its key role in the inflammatory cytokine network and macrophage biology of fish.

Functional characterization of TNF-α in grass carp head kidney leukocytes: induction and involvement in the regulation of NF-κB signaling

Tumor necrosis factor-alpha (TNF-α) is a potent regulatory cytokine, which serves as a key mediator of inflammation, immunity and apoptosis in mammals. Identification, expression and regulatory effects of TNF-α have been reported in various fish species, showing the structural and functional similarity or discrepancy between each other. In this study, TNF-α was identified from grass carp (Ctenopharyngodon idella) and the deduced grass carp TNF-α (gcTNF-α) protein possessed the TNF family signature motifs, a protease cleavage site, a transmembrane domain and two conserved cysteine residues. Further studies showed that gcTNF-α expression was induced with a rapid kinetics by immune challenge in vitro and in vivo. To characterize the function of gcTNF-α, recombinant gcTNF-α (rgcTNF-α) was prepared by using the Escherichia coli expression system. It was shown to enhance the mRNA expression of gcTNF-α and gcIL-1β in head kidney leukocytes (HKLs), confirming the biological activity of rgcTNF-α. In the same model, NF-κB inhibitor (PDTC) was able to attenuate rgcTNF-α-induced gcTNF-α mRNA expression, implying the involvement of NF-κB pathway in fish TNF-α action. This notion was reinforced by the finding that rgcTNF-α could induce the phosphorylation of IκBα in a time-dependent oscillation in HKLs, indicating a dynamical variation of NF-κB activity as seen in mammals. In addition, rgcTNF-α could up-regulate the expression of two TNF receptor-associated factors (TRAF), TRAF1 and TRAF2, in a time- and dose-dependent manner, suggesting that gcTNF-α may function as a regulator of fish NF-κB pathway. These results for the first time reveal the link of gcTNF-α to the NF-κB pathway and provide a better understanding of TNF-α signaling in teleost immunity.

[Molecular cloning, sequence analysis and expression of ayu complement component C9 gene]

C9, a component of the membrane attack complex, participates in the final stage of the complement cascade which lyses foreign organisms by disrupting the integrity of their cell membranes. In the present study, a full-length ayu C9 (aC9) cDNA was cloned which contains 2,125 nucleotides and encodes a protein of 592 amino acids. A signal peptide was deposited in the N-terminal 22 residues. The deduced amino acid sequence of aC9 showed 56.8% identity to the C9 of rainbow trout, and 40.9% to 53.8% identity to the C9 of other teleosts. RT-PCR analysis demonstrated that the mRNA of aC9 was expressed in the liver, spleen, intestine, gill and muscle of healthy ayu fish with the highest level in the liver. Quantitative RT-PCR analysis showed that aC9 transcripts were significantly up-regulated in the liver at 4 h post Listonella anguillarum infection, peaked at 16 h post injection. Western blotting analysis revealed that serum aC9 significantly increased in Listonella anguillarum infected ayu fish. Our results suggested that aC9 may play an important role in fish immune response of anti-bacteria.

Use of suppressive subtractive hybridization to identify differentially expressed genes in ayu (Plecoglossus altivelis) associated with Listonella anguillarum infection

Suppressive subtractive hybridization (SSH) was employed to identify differentially expressed genes in ayu (Plecoglossus altivelis) associated with Listonella anguillarum infection. 800 random clones were selected from forward and reverse subtractive libraries and 787 were successfully sequenced. After assembling, 105 contigs and 414 singletons were finally obtained, some of which were immune-related genes. A real-time quantitative PCR (RT-qPCR) analysis of the expression patterns of 28 transcripts showed that the false-positive rate was approximately 7.1%. Furthermore, Wap65-2 was overexpressed in Escherichia coli, purified and used for antiserum preparation. Western blot analysis revealed that serum Wap65-2 of ayu significantly increased after bacterial infection, suggesting that it was a positive acute-phase protein (APP).

Microarray analysis of gene expression in disk abalone Haliotis discus discus after bacterial challenge

In this study, we investigated the gene expression profiling of disk abalone, Haliotis discus discus challenged by a mixture of three pathogenic bacteria Vibrio alginolyticus, Vibrio parahemolyticus, and Listeria monocytogenes using a cDNA microarray. Upon bacteria challenge, 68 (1.6%) and 112 (2.7%) gene transcripts changed their expression levels ≥2 or ≤2 -fold in gills and digestive tract, respectively. There were 46 tissue-specific transcripts that up-regulated specifically in the digestive tract. In contrast, only 13 transcripts showed gill-specific up-regulation. Quantitative real-time PCR was performed to verify microarray data and results revealed that candidate genes namely Krüppell-like factor (KLF), lachesin, muscle lim protein, thioredoxin-2 (TRx-2), nuclear factor interleukin 3 (NFIL-3) and abalone protein 38 were up-regulated. Also, our results further indicated that bacteria challenge may activate the transcription factors or their activators (Krüppell-like factor, inhibitor of NF-κB or Ik-B), inflammatory cytokines (IL-3 regulated protein, allograft inflammatory factor), other cytokines (IFN-44-like protein, SOCS-2), antioxidant enzymes (glutathione-S-transferase, thioredoxin-2 and thioredoxin peroxidase), and apoptosis-related proteins (TNF-α, archeron) in abalone. The identification of immune and stress response genes and their expression profiles in this microarray will permit detailed investigation of the stress and immune responses of abalone genes.

The expression of two novel orange-spotted grouper (Epinephelus coioides) TNF genes in peripheral blood leukocytes, various organs, and fish larvae

The tumour necrosis factor (TNF) super-family is a group of important cytokines involved in inflammation, apoptosis, cell proliferation, and the general stimulation of the immune system. The TNF gene has been cloned in some bony fish; however, its counterparts are still unidentified in the majority of fish species. In this study, we cloned gTNF-1 and gTNF-2 from the orange-spotted grouper (Epinephelus coioides), an economically important farmed fish. Both genes include 4 exons and 3 introns and encoded 253 and 241 amino acid proteins with a molecular weight of approximately 27 and 26 kDa, respectively. The identity of the putative amino acid sequences between gTNF-1 and gTNF-2 was only 38%. The positions of cysteine residues, a protease cleavage site, and a transmembrane domain sequence derived from gTNF-1 and gTNF-2 were similar to those in other fish and mammalian TNF-α. The mRNA expression levels of the 2 gTNF molecules were evaluated in unstimulated/stimulated peripheral blood leukocytes, various organs, and fish larvae. Following lipopolysaccharide (LPS) treatment, gTNF-2 was expressed at higher levels, was up-regulated more quickly, and was more sensitive to the immune response than gTNF-1. gTNF-1 was constitutively expressed in the thymus, brain, and spleen, but it was also expressed in the heart, head kidney, and trunk kidney after LPS stimulation. gTNF-2 was constitutively expressed in the thymus, head kidney, trunk kidney, spleen, and intestine; further, gTNF-2 was highly expressed in all organs post-LPS stimulation. Finally, the gTNF expression levels were evaluated at various developmental stages in grouper larvae. A higher variation of gTNF expression levels was observed in fish larvae from a contaminated hatchery. This study revealed the different expression patterns of gTNF-1 and gTNF-2. In addition, gTNF-2 was more sensitive to pathogens than gTNF-1; therefore, it may be an appropriate marker for pathogen invasion and the evaluation of the larval rearing environment.

Direct involvement of tumor necrosis factor-α in the regulation of glucose uptake in rainbow trout muscle cells

The proinflammatory cytokine TNF-α is known to have a direct action on skeletal muscle in mammals. However, little is known regarding the potential effects of cytokines on nonimmune tissues, particularly in skeletal muscle, in fish. The aim of this study was to investigate the effects of recombinant trout TNF-α (rtTNF-α) on skeletal muscle carbohydrate metabolism in rainbow trout (Oncorhynchus mykiss). We used a primary cell culture of muscle cells from rainbow trout to show that rtTNF-α stimulates glucose uptake in myoblasts and myotubes at concentrations that do not affect the viability of the cells, requiring de novo protein synthesis as shown by the impairment of rtTNF-α-stimulated glucose uptake by cycloheximide. With the use of specific inhibitors, we show that rtTNF-α-stimulated glucose uptake is mediated by the p38MAPK, NF-κB, and JNK pathways. Additionally, we provide evidence that the stimulatory effects of rtTNF-α on glucose uptake in trout skeletal muscle cells may be caused, at least in part, by an increase in the amount of GLUT4 at the plasma membrane. Incubation of trout muscle cells with conditioned medium from LPS-stimulated trout macrophages, enriched in TNF-α, increased glucose uptake. Our results indicate that recombinant, as well as native trout TNF-α, directly stimulates glucose uptake in trout muscle cells and provide evidence, for the first time in nonmammalian vertebrates, for a potential regulatory role of TNF-α in skeletal muscle metabolism.

Molecular cloning of rock bream (Oplegnathus fasciatus) tumor necrosis factor-alpha and its effect on the respiratory burst activity of phagocytes

Rock bream (Oplegnathus fasciatus) tumor necrosis factor-alpha (rbTNF-alpha) gene was cloned, recombinantly produced, and the effect of the recombinant rbTNF-alpha on the respiratory burst activity of rock bream phagocytes was analyzed. Structurally, genomic DNA of rbTNF-alpha was comprised with four exons and three introns, and deduced amino acid sequence of its cDNA possessed the TNF family signature, a transmembrane domain, a protease cleavage site, and two cysteine residues, which are the typical characteristics of TNF-alpha gene in mammals and fish. The chemiluminescent (CL) response of rock bream phagocytes was significantly enhanced by pre-incubation with recombinant rbTNF-alpha, when opsonized zymosan was used as a stimulant of the respiratory burst. However, CL enhancing effect of the recombinant rbTNF-alpha was very weak when the respiratory burst activity of phagocytes was triggered with phorbol-12-myristate-13-acetate (PMA) instead of zymosan. These results suggest that rock bream TNF-alpha might have an ability to prime the respiratory burst activity of phagocytes against receptor-mediated phagocytosis inducing stimulants, such as zymosan, but have little ability against stimulants not accompanying receptor-mediated phagocytosis.

Two types of tumor necrosis factor-alpha in bluefin tuna (Thunnus orientalis) genes: Molecular cloning and expression profile in response to several immunological stimulants

Tumor necrosis factor-alpha (TNF-alpha) is a key inflammatory mediator and has also the potential as a prominent biomarker of innate immunity. In this study, we identified and characterized TNF-alpha from bluefin tuna, which is an important cultured species. Two types of TNF-alpha were also cloned incidentally (TNF1 and TNF2). The open reading frame of TNF1 and TNF2 cDNA encoded 247 and 245 amino acids, respectively. The amino acid sequence identity among sea perch, red sea bream, and tiger puffer was 73, 70, 59% for TNF1 and 49, 51, 45% for TNF2, respectively. The identity between TNF1 and TNF2 amino acid sequences of the bluefin tuna was only 43%. The positions of cysteine residues, transmembrane sequence, and protease cleavage site in bluefin tuna TNFs were similar with other reported fish and mammalian TNF-alpha. In a phylogenetic analysis, TNF1 is grouped with other reported Perciformes TNF-alpha. On the other hand, TNF2 is grouped with ayu TNF and is quite distant from the fish TNF-alpha group and lymphotoxin-beta group. While TNF1 mRNA showed no significant difference in all tissues, TNF2 mRNA was expressed significantly higher in the blood than in the gill, intestine, head kidney, spleen, heart, and ovary. In peripheral blood leucocytes (PBL), expressions of TNF2 mRNA were significantly increased by stimulation with lipopolysaccharide, phytohemagglutinin, concanavalin A, pokeweed mitogen, phorbol myristate acetate in vitro, but those of TNF1 were not. Recombinant mature TNF1 and TNF2 proteins significantly enhanced phagocytic activity of PBL. Our results suggest that bluefin tuna possess two types of TNF-alpha homologue, and TNF2 is a potential biomarker for innate immunity.

A novel Fas ligand in mollusk abalone: molecular characterization, immune responses and biological activity of the recombinant protein

Fas ligand is a member of the TNF superfamily that plays an important role by inducing apoptosis and homeostasis of immune responses. The gene encoding Fas ligand was isolated from a disk abalone (Haliotis discus discus) cDNA library, denoted as the AbFas ligand. It contains an 1832bp transcript with a 945bp open reading frame, encoding 315 amino acids. The AbFas ligand showed characteristic transmembrane and TNF family signature domains. The deduced amino acid comparison showed that the AbFas ligand exhibits 22.0, 16.1 and 14.5% identities to human Fas ligand, TNF-alpha, and lymphotoxin (LT-alpha), respectively. Phylogenetic analysis indicates that the AbFas ligand belongs to the invertebrate TNF family and it is closely related to vertebrate Fas ligand counterparts. Quantitative real-time PCR analysis results showed that the AbFas ligand transcripts were constitutively expressed in abalone hemocytes, gills, mantle, muscle, digestive tract and digestive gland in a tissue-specific manner. By immune stimulation, AbFas ligand mRNA was significantly (p<0.05) up-regulated after infection with a mixture of bacteria (Vibrio alginolyticus, Vibrio parahemolyticus, and Listeria monocytogenes), viral haemorrhagic septicaemia virus (VHSV), and lipopolysaccharide (LPS) in abalone gills. The recombinant AbFas ligand was over-expressed in Escherichia coli (E. coli) and purified using a pMAL protein fusion system. This recombinant AbFas ligand showed its biological activity by inducing both superoxide anion (O(2-) and H(2)O(2) in human THP-1 cells in concentration-dependant manner. Correlating the AbFas ligand transcriptional up-regulation against bacteria, virus and LPS with the biological activity of its recombinant protein, we could suggest that the abalone Fas ligand may control microbial infection by inducing O(2-), H(2)O(2) and other ROS.

Cloning and expression analysis of three striped trumpeter (Latris lineata) pro-inflammatory cytokines, TNF-alpha, IL-1beta and IL-8, in response to infection by the ectoparasitic, Chondracanthus goldsmidi

This study reports the cloning and sequencing of three striped trumpeter (Latris lineata Forster) pro-inflammatory cytokines, TNF-alpha, IL-1beta and IL-8, as well as their differential expression in response to an infection by the ectoparasite Chondracanthus goldsmidi. The striped trumpeter TNF-alpha transcript consisted of 1093 bp, including a 759 bp ORF which translated into a 253 aa transmembrane peptide. The sequence contained a TACE cut site, that would produce a 167 aa soluble peptide containing the TNF ligand family signature. The IL-1beta sequence consisted of 963 bp, including a 774 bp ORF which translated into a 258 aa protein. The protein lacked both a signal peptide and an ICE cleavage site, but did contain the IL-1 family signature. The sequence for the chemokine IL-8 contained 906 bp, with an ORF of 297 bp, which translated into a 99 aa protein. The protein lacked an ELR motif as is common with many teleost IL-8 sequences. The differential expression of the three cytokine genes in parasitized fish was investigated via quantitative real-time PCR. A significant up-regulation of all three pro-inflammatory cytokines was found in the gills, which were the site of parasite attachment. Examination of head kidney cells revealed a significant up-regulation of TNF-alpha, but not IL-1beta or IL-8. Conversely, the spleen cells showed significant up-regulation of both IL-1beta and IL-8, but not TNF-alpha. These findings allow for more detailed investigations of the striped trumpeter immune response.

First molluscan TNF-alpha homologue of the TNF superfamily in disk abalone: molecular characterization and expression analysis

Tumor necrosis factor alpha (TNF-alpha) is considered as a multifunctional immune modulator that plays an important role in the innate and adaptive immune systems in vertebrates. Here, we described the characterization and expression analysis of the first TNF-alpha homologue in mollusk abalone, named as AbTNF-alpha. It has 930-bp full length with a 717-bp open reading frame (ORF), encoding 239 amino acids. The AbTNF-alpha amino acid sequence shows the characteristic TNF family signature, N-terminal transmembrane domain consisting of a hydrophobic amino acid cluster and cell attachment sequence at (155)RGD(157). Phylogenic analysis results showed that AbTNF-alpha is more related to the invertebrate Ciona savignyi TNF superfamily ligand member (CsTL). Quantitative real-time PCR expression results showed that AbTNF-alpha was constitutively expressed in both immune and non-immune tissues in a tissue specific manner. The highest constitutive expression was in the gill tissue with a 1.5-fold compared to hemocytes expression. The AbTNF-alpha mRNA expression in gill tissue was monitored in vivo stimulated by a mixture of pathogenic bacteria (Vibrio alginolyticus, Vibrio parahemolyticus, and Lysteria monocytogenes), viral haemorrhagic septicaemia virus (VHSV) and lipopolysaccharide (LPS). The AbTNF-alpha expression was significantly (p<0.05) induced by bacteria, VHSV and LPS compared to the control animals. Moreover, the highest level expressions of each induction were at 24 h (5.2-fold), 48 h (2.8-fold), and 48 h (3.3-fold) by bacteria mixture, VHSV and LPS, respectively. These results indicate that AbTNF-alpha could respond to pathogenic infection or stimulation and may play an important role in the abalone immune system.

A novel tumor necrosis factor ligand superfamily member (CsTL) from Ciona savignyi: molecular identification and expression analysis

A novel invertebrate TNF ligand was identified and characterized in Ciona savignyi. The CsTL cDNA consisted of 995 nucleotides and encoded 281 amino acids. A conserved TNF family signature and several motifs of TNF ligand superfamily were identified in deduced amino acid sequence of CsTL. Phylogenetic analysis grouped CsTL, CiTNF (predicted TNF ligand superfamily homolog in Ciona intestinalis) and urchin TL1A with their own cluster apart from mammalian TNFalpha, LTA, TNFSF15 and fish TNFalpha proteins. Expression studies demonstrated that CsTL mRNA is present in all tested tissues from unchallenged ascidians and its expression was significantly upregulated in hemocytes following LPS injection. The recombinant CsTL protein expressed using a baculovirus expression system showed potential cytotoxic activity in L929 cells. Present results indicated that TNF ligand superfamily molecules are present in marine invertebrates.