Molecular characterization of tumor necrosis factor receptors 1 and 2 of the goldfish (Carassius aurutus L.)

The goldfish primary kidney macrophage system

Miodrag (Mike) Belosevic and collaborators profoundly influenced the development of primary kidney macrophage culturing system (PKM) to study fish immunology in various aspects of comparative immunology. Their application of using PKM model, opened a new path for studying the development of macrophages, regulation of hematopoiesis, and cell specific response against various pathogens. By measuring histopathological and immunological outcomes, the biological implications of a variety of cytokines and signal transduction molecules could be elucidated with the established PKM system. A variety of growth factors mediating hematopoiesis and cytokines regulating the immune responses were functionally characterized, which served as a fundamental basis for making goldfish an excellent model to study fish immunology. Specifically, using in vivo and PKM based in vitro assays, the Belosevic lab advanced the goldfish-M. marinum model to study the anti-mycobacteria responses in teleosts, thus paving a way for the development of novel therapeutic approaches which could be applied in aquaculture settings or utilized as a model for human disease. In this review, we will look at the contribution of Dr. Mike Belosevic to teleost macrophage development, multiple cytokine functional characterization, and host-pathogen interactions.

The acute inflammatory response of teleost fish

Acute inflammation is crucial to the immune responses of fish. The process protects the host from infection and is central to induction of subsequent tissue repair programs. Activation of proinflammatory signals reshapes the microenvironment within an injury/infection site, initiates leukocyte recruitment, promotes antimicrobial mechanisms and contributes to the resolution of inflammation. Inflammatory cytokines and lipid mediators are primary contributors to these processes. Uncontrolled or persistent induction results in delayed tissue healing. The kinetics by which inducers and regulators of acute inflammation exert their actions is essential for understanding the pathogenesis of fish diseases and identifying potential treatments. Although, a number of these are well-conserved across, others are not, reflecting the unique physiologies and life histories of members of this unique animal group.

Characterization of the pro-inflammatory roles of the goldfish (Carassius auratus L.) M17 protein

The interleukin-6 family of cytokines possesses a diversity of roles with significant redundancy. The roles of these molecules have been relatively well characterized in mammals, with limited attention in other species. Progress has been made in the discovery of homologous molecules in fish. Here we report the characterization of pro-inflammatory properties of recombinant goldfish M17. Recombinant goldfish M17 enhanced phagocytosis, primed production of reactive oxygen intermediates, and was chemotactic to macrophages. Treatment of goldfish macrophages with LPS, heat-killed and live Aeromonas hydrophila resulted in higher M17 mRNA levels. Recombinant M17 (RgM17) induced dose-dependent production of IFNγ and IL-1β1 in goldfish macrophages. Furthermore, treatment of macrophages with rgM17 resulted in upregulation of transcription factors that were important in the differentiation of myeloid progenitors into monocytes/macrophages (Runx1 and GATA2). Our results indicate that goldfish M17 is an essential inflammatory cytokine for proliferation and differentiation of goldfish progenitor cells.

TNFR2 is a regulatory target of pol-miR-194a and promotes the antibacterial immunity of Japanese flounder Paralichthys olivaceus

MicroRNAs (miRNAs) are regulatory RNAs that modulate target gene expression after transcription. Pol-miR-194a had been reported to be a miRNA of Japanese flounder (Paralichthys olivaceus) involved in Edwardsiella tarda infection. Here, we identified tumor necrosis factor receptor 2 (TNFR2) as a target gene of pol-miR-194a. Pol-miR-194a markedly repressed the protein expression of flounder TNFR2 (PoTNFR2) via specific interaction with the 3'UTR of PoTNFR2. PoTNFR2 responded to E. tarda infection in a manner that was opposite to that of pol-miR-194a and inhibited E. tarda invasion by activating the NF-κB pathway. Consistently, dysregulation of PoTNFR2 had a significant impact on E. tarda dissemination in flounder tissues. Together, these results add new insights into the regulation mechanism and immune function of fish TNFR2 and pol-miR-194a.

Molecular Characterization, Evolution and Expression Analysis of TNFSF14 and Three TNFSF Receptors in Spotted Gar Lepisosteus oculatus

The tumor necrosis superfamily (TNFSF) and their receptors (TNFRs) play an essential role in inflammatory responses. In this study, tnfsf14, tnfrsf1a, tnfrsf1b and tnfrsf14 were identified in spotted gar. All the genes have conserved genomic organization and synteny with their respective homologs in zebrafish and humans. The putative TNFSF protein contains a typical TNF homology domain in the extracellular region. All three TNFRSFs possess characteristic cysteine-rich domains. TNFRSF1a has a death domain in the cytosolic region which is absent in the TNFRSF1b and TNFRSF14. Notably, TNFRSF14 lacks a transmembrane domain and is predicted to be secreted. Protein structure modeling revealed that the key residues involved in the interaction between TNFSF14 and TNFRSF14 are well conserved in spotted gar. All four genes were ubiquitously expressed in the spleen, liver, kidney, gills and intestine. Infection with Klebsiella pneumoniae resulted in remarkable downregulation of tnfsf14 and tnfrsf14 in tissues but upregulation of tnfrsf1a and tnfrsf1b. The results indicate that tnfsf14, tnfrsf1a, tnfrsf1b and tnfrsf14 are involved in the immune response to bacterial infection, and expand knowledge on the TNF system in the primitive ray-finned fish.

Structures, evolutionary relationships and expression profiles of the tumour necrosis factor superfamily and their receptors in black rockfish (Sebastes schlegelii)

Members of tumour necrosis factor superfamily (TNFSF) and TNF receptor superfamily (TNFRSF) have crucial roles in many important biological processes such as cell proliferation, cell death, development, survival, immunity, and various diseases. The human TNFSF consists of 19 ligands and 29 receptors. Compared with those in human, fish have most of the TNFSF and receptors that have been found in mammals, while some of the homologues are specific or lost in fish. Especially, no systematic report on the identification of TNFSF ligands and their receptors in S. schlegelii. Therefore, to investigate the characterization and molecular evolution of TNFSF and TNFRSF genes in Sebastes schlegelii, we performed a genome-wide survey and identified 14 TNFSFs and 24 TNFRSFs from S. schlegelii. In S. schlegelii, we found duplication events occurred in TNFSF2, TNFSF6, TNFSF10, TNFSF13, TNFSF14, TNFRSF5, TNFRSF6, TNFRSF6B, TNFRSF10B, TNFRSF16, and TNFRSF19 genes. Among which, the tandem duplications events occurred in TNFSF13 and TNFRSF6, and the whole genome duplications events occurred in the remaining TNFSF and TNFRSF genes. Based on the molecular phylogenetic analysis, 14 TNFSFs were divided into three different clusters and 24 TNFRSFs were classed as three distinct subgroups, respectively. Meanwhile, protein domains and motifs analysis revealed that TNFSF contain homology domain (THD), and TNFRSF have typical cysteine-rich domains (CRDs). Synteny results indicates that the TNFSFs and TNFRSFs neighborhood genes have taken place great changes compared to those in human, fugu and zebrafish. Meanwhile, qRT-PCR results demonstrated that most TNFSFs and TNFSRSFs were significantly differentially expressed in gill, skin and intestine after E. tarda infection with time-dependent manners. In addition, protein-protein interaction network (PPI) analysis indicated that the most related genes connecting to TNFSF and TNFRSFs were TNFSF ligands and receptors. In summary, this study provided a new understanding for characterization and evolution of the TNFSF genes and their receptors in S. schlegelii.

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.

Two types of TNF-α and their receptors in snakehead (Channa argus): Functions in antibacterial innate immunity

Tumor necrosis factor-α (TNF-α) is a pluripotent mediator of pro-inflammatory and antimicrobial defense mechanisms and a regulator of lymphoid organ development. Although two types of TNF-α have been identified in several teleost species, their functions in pathogen infection remain largely unexplored, especially in pathogen clearance. Herein, we cloned and characterized two types of TNF-α, termed shTNF-α1 and shTNF-α2, and their receptors, shTNFR1 and shTNFR2, from snakehead (Channa argus). These genes were constitutively expressed in all tested tissues, and were induced by Aeromonas schubertii and Nocardia seriolae in head kidney and spleen in vivo, and by lipoteichoic acid (LTA), lipopolysaccharides (LPS), and Polyinosinic-polycytidylic acid [Poly (I:C)] in head kidney leukocytes (HKLs) in vitro. Moreover, recombinant shTNF-α1 and shTNF-α2 upregulated the expression of endogenous shTNF-α1, shTNF-α2, shTNFR1, and shTNFR2, and enhanced intracellular bactericidal activity, with shTNF-α1 having a greater effect than shTNF-α2. These findings suggest important roles of fish TNFα1, TNFα2, and their receptors in bacterial infection and pathogen clearance, and provide a new insight into their function in antibacterial innate immunity.

Different origins of paralogues of salmonid TNR1 and TNFR2: Characterisation and expression analysis of four TNF receptor genes in rainbow trout Oncorhynchus mykiss

Mammalian TNFR1 and TNFR2 bind TNFα and TNFβ, and provide key communication signals to a variety of cell types during development and immune responses that are crucial for cell survival, proliferation and apoptosis. In teleost fish TNFβ is absent but TNFα has been expanded by the third whole genome duplication (3R WGD) and again by a 4R WGD in some lineages, leading to the four TNFα paralogues known in salmonids. Two paralogues for each of TNFR1 and TNFR2 have been cloned in rainbow trout in this study and are present in other salmonid genomes. Whilst the TNFR2 paralogues were generated via the 4R salmonid WGD, the TNFR1 paralogues arose from a local en bloc duplication. Functional diversification of TNFR paralogues was evidenced by differential gene expression and modulation, upstream ATGs affecting translation, ATTTA motifs in the 3'-UTR regulating mRNA stability, and post-translational modification by N-glycosylation. Trout TNFR are highly expressed in immune tissues/organs, and other tissues, in a gene- and tissue-specific manner. Furthermore, their expression is differentially modulated by PAMPs and cytokines in a cell type- and stimulant-specific manner. Such findings suggest an important role of the TNF/TNFR axis in the immune response and other physiological processes in fish.

Identification and functional characterization of grass carp (Ctenopharyngodon idella) tumor necrosis factor receptor 2 and its soluble form with potentiality for targeting inflammation

Tumor necrosis factor-alpha (TNF-α) signals through two distinct cell surface receptors, TNFR1 and TNFR2 in mammals. In the present study, grass carp Tnfr2 (gcTnfr2) was isolated and characterized. Sequence alignment and phylogenetic analysis suggested that gcTnfr2 was a homolog of goldfish and zebrafish Tnfr2. Tissue distribution assay showed gctnfr2 transcripts were expressed in all examined tissues similar to gctnfr1. To functionally characterize the newly cloned molecule, gcTnfr2 was overexpressed in COS7 cell lines and it showed the ability to mediate the recombinant grass carp Tnf (rgcTnf)-α-triggered NF-κΒ activity and gcil1b promoter activity, clarifying its role in mediating Tnf-α signaling. The recombinant soluble form of gcTnfr2 (rgcsTnfr2) was prepared and it was able to interact with rgcTnf-α with higher affinity than that of rgcsTnfr1. Moreover, grass carp soluble Tnfr2 (gcsTnfr2) were detected in the culture medium of grass carp head kidney leukocytes (HKLs) and heat-inactivated A. hydrophila challenge significantly induced its production, indicating involvement of gcsTnfr2 in inflammation response. In agreement with this notion, rgcsTnfr2 effectively antagonized the effect of rgcTnf-α on il1b mRNA expression in HKLs, suggesting anti-Tnf-α property of gcsTnfr2. To strengthen the anti-inflammatory role of soluble Tnfr2, bacteria were injected intraperitoneally in grass carp followed by rgcsTnfr2. Hematoxylin-eosin (HE) staining of head kidney, spleen and intestine showed that rgcsTnfr2 could significantly improve infection-induced histopathological changes. These results functionally identified gcTnfr2 and its soluble form, particularly highlighting the role of gcsTnfr2 against Tnf-α-triggered inflammatory signaling. In this line, rgcsTnfr2 displayed anti-inflammatory potentiality during infection, thereby providing a powerful mediator of inflammation control in fish.

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 functional characterization of tumor necrosis factor receptor 1 (TNFR1) of grass carp (Ctenopharyngodon idella)

Tumor necrosis factor-alpha (TNF-α) exerts its regulatory effects by binding one of two TNF receptors, TNF-α receptor 1 (TNFR1) or TNFR2. In this study, we isolated and identified the cDNA sequence of grass carp TNFR1 (gcTNFR1). Similar to its homologs in other fish species, the putative protein of gcTNFR1 possessed an extracellular region containing three TNF homology domains, a transmembrane region and a cytoplasmic region with a conserved death domain. Consistent with the widespread expression of mammalian TNFR1, gcTNFR1 transcripts ubiquitously expressed in spleen, thymus, liver, heart, gill, intestine, brain and head kidney with the highest expression levels in head kidney. To reveal its inductive expression patterns in inflammatory response, effect of in vivo bacterial infection on gcTNFR1 gene expression was examined, showing a rapid increase of gcTNFR1 expression in head kidney, gill, liver and intestine, which is consistent with the role of TNF-α as an early response gene during immune challenges. To define the functional role of gcTNFR1, recombinant extracellular region of gcTNFR1 (rgcTNFR1) was prepared and used to perform in vitro binding assay, demonstrating its ability to interact with recombinant grass carp TNF-α (rgcTNF-α). Furthermore, to characterize the function of gcTNFR1 in affecting rgcTNF-α actions, the effect of overexpressing gcTNFR1 on rgcTNF-α-induced grass carp IL-1β (gcIL-1β) promoter activity was determined in COS7 cells. Results showed that gcTNFR1 was involved in the regulation of rgcTNF-α on gcIL-1β transcription. Consistently, rgcTNFR1 was effective in attenuating the effect of rgcTNF-α on IL-1β mRNA expression in grass carp head kidney leukocytes, providing evidence for the involvement of TNFR1 in TNF-α signaling in grass carp. These data facilitate a better understanding of TNF-α receptor signaling in grass carp.

Molecular and functional characterization of goldfish (Carassius auratus L.) Serum Amyloid A

Quantitative expression analysis of goldfish SAA revealed the highest mRNA levels in the kidney, spleen and intestine with lower mRNA levels in muscle and liver. Goldfish SAA was differentially expressed in goldfish immune cells with highest mRNA levels observed in neutrophils. To functionally assess goldfish SAA, recombinant protein (rgSAA) was generated by prokaryotic expression and functionally characterized. Monocytes and macrophages treated with rgSAA exhibited differential gene expression of pro-inflammatory and anti-inflammatory cytokines. rgSAA induced gene expression of both pro-inflammatory (TNFα1, TNFα2) and anti-inflammatory cytokines (IL-10, TGFβ) in monocytes. rgSAA induced IL-1β1 and SAA gene expression in macrophages. rgSAA was chemotactic to macrophages and neutrophils, but not monocytes. rgSAA did not affect respiratory burst induced by heat-killed Aeromonas salmonicida. rgSAA treatment of macrophages down-regulated their production of nitric oxide. rgSAA exhibited antibacterial properties against Escherichia coli in a concentration dependent manner.

Biology of Bony Fish Macrophages

Macrophages are found across all vertebrate species, reside in virtually all animal tissues, and play critical roles in host protection and homeostasis. Various mechanisms determine and regulate the highly plastic functional phenotypes of macrophages, including antimicrobial host defenses (pro-inflammatory, M1-type), and resolution and repair functions (anti-inflammatory/regulatory, M2-type). The study of inflammatory macrophages in immune defense of teleosts has garnered much attention, and antimicrobial mechanisms of these cells have been extensively studied in various fish models. Intriguingly, both similarities and differences have been documented for the regulation of lower vertebrate macrophage antimicrobial defenses, as compared to what has been described in mammals. Advances in our understanding of the teleost macrophage M2 phenotypes likewise suggest functional conservation through similar and distinct regulatory strategies, compared to their mammalian counterparts. In this review, we discuss the current understanding of the molecular mechanisms governing teleost macrophage functional heterogeneity, including monopoetic development, classical macrophage inflammatory and antimicrobial responses as well as alternative macrophage polarization towards tissues repair and resolution of inflammation.

The analysis of the acute phase response during the course of Trypanosoma carassii infection in the goldfish (Carassius auratus L.)

The expression of genes encoding the acute phase proteins (APP) during the course of Trypanasoma carassii infection in the goldfish was determined using quantitative PCR. Significant changes in the mRNA levels of ceruloplasmin (Cp), C-reactive protein (CRP), transferrin (Tf), hemopexin (Hx) and serum amyloid A (SAA) were observed in the kidney, liver and spleen at various days post infection (dpi). Of the five acute phase protein genes examined, CRP and SAA exhibited the highest expression in the tissues during the acute infection. Cp and Tf were up-regulated throughout the acute course of infection in the liver. During the chronic phase of the infection, APP expression in the liver was similar to that in the non-infected control fish. At 7 dpi, Cp, Tf and Hx were down-regulated in the spleen, and Cp and Tf kidney, but their mRNA levels gradually returned to those of control non-infected fish. In contrast, during the chronic phase of the infection, there was an up-regulation of Cp, Hx and Tf in the spleen, and Tf and SAA in the kidney. The goldfish CRP was cloned and functionally characterized. CRP was differentially expressed in normal goldfish immune cells, with highest expression in monocytes and lowest expression in mature macrophages. A recombinant goldfish CRP (rgfCRP) was generated using prokaryotic expression. rgfCRP enhanced complement-mediated killing of trypanosomes in vitro, and the lysis increased after addition of immune serum. rgfCRP did not affect the production of reactive oxygen and nitrogen intermediates by monocytes and macrophages, respectively.

Functional characterization of viral tumor necrosis factor receptors encoded by cyprinid herpesvirus 3 (CyHV3) genome

Cyprinid herpesvirus 3 (CyHV3) is a large double-stranded DNA virus of Alloherpesviridae family in the order Herpesvirales. It causes significant morbidity and mortality in common carp and its ornamental koi variety, and threatens the aquaculture industries worldwide. Mimicry of cytokines and cytokine receptors is a particular strategy for large DNA viruses in modulating the host immune response. Here, we report the identification and characterization of two novel viral homologues of tumor necrosis factor receptor (TNFR) encoded by CyHV3-ORF4 and -ORF12, respectively. CyHV3-ORF4 was identified as a homologue of HVEM and CyHV3-ORF12 as a homologue of TNFRSF1. Overexpression of ORF4 and ORF12 in zebrafish embryos results in embryonic lethality, morphological defects and increased apoptosis. Although we failed to identify any interaction between the two vTNFRs and their potential ligands in zebrafish TNF superfamily by yeast two-hybrid system, the expression of some genes in TNF superfamily or TNFR superfamily were mis-regulated in ORF4 or ORF12-overexpressing embryos, especially the death receptor zHDR and its cognate ligand DL1b. Further studies showed that the apoptosis induced by the both CyHV3 vTNFRs is mainly activated through the intrinsic apoptotic pathway and requires the crosstalk between the intrinsic and extrinsic apoptotic pathway. Additionally, using RT-qPCR and Western blot assays, the expression patterns of the both vTNFRs were also analyzed during CyHV3 productive infection. Collectively, this is the first functional study of two unique vTNFRs encoded by a herpesvirus infecting non-mammalian vertebrates, which may provide novel insights into viral immune regulation mechanism and the pathogenesis of CyHV3 infection.

Functional characterization of receptor-interacting serine/threonine kinase 2 (RIP2) of the goldfish (Carassius auratus L.)

We report on the functional characterization of RIP2 of the goldfish. Quantitative expression analysis of goldfish RIP2 revealed the greatest mRNA levels in the spleen, monocytes and splenocytes. We generated a recombinant form of the molecule (rgRIP2) and determined that anti-human RIP2 polyclonal antibody specifically recognized recombinant goldfish RIP2 (rgRIP2). Goldfish RIP2 activity was inhibited by the p38 MAPK pathway inhibitor SB203580. Treatment of goldfish macrophages with LPS, PGN, MDP, Poly I:C, heat-killed and live Mycobacterium marinum, and heat-killed Aeromonas salmonicida differentially changed the expression of RIP2 at both mRNA and protein levels. Co-immunoprecipitation assays indicated that RIP2 interacted with Nod1 and Nod2 receptors in eukaryotic cells. The results of dual luciferase reporter assay revealed that RIP2 over-expression caused the activation of the NF-κB signal pathway. In addition, RIP2 was involved in the regulation of the production of TNFα-2 and IL-1β1 in goldfish macrophages exposed to M. marinum.

Advanced analytical mass spectrometric techniques and bioassays to characterize untreated and ozonated oil sands process-affected water

Oil sands process-affected water (OSPW) is a toxic and poorly biodegradable mixture of sand, silt, heavy metals, and organics. In this study, qualitative and quantitative comparisons of naphthenic acids (NAs) were done using ultraperformance liquid chromatography time-of-flight mass spectrometry (UPLC TOF-MS), Fourier transform ion cyclotron resonance (FT-ICR) MS, and ion mobility spectrometry (IMS). The unique combination of these analyses allowed for the determination and correlation of NAs, oxidized NAs, and heteroatom (sulfur or nitrogen) NAs. Despite its lower resolution, UPLC-TOF MS was shown to offer a comparable level of reliability and precision as the high resolution FT-ICR MS. Additionally, the impacts of ozonation (35 mg/L utilized ozone dose) and subsequent NAs degradation on OSPW toxicity were assessed via a collection of organisms and toxicity end points using Vibrio fischeri (nonspecific), specific fish macrophage antimicrobial responses, and fish olfactory responses. Fish macrophages exposed to ozonated OSPW for 1 week showed higher production of reactive oxygen and nitrogen intermediates; however, after 12 weeks the responses were reduced significantly. Fish olfactory tests suggested that OSPW interfered with their perception of odorants. Current results indicate that the quantification of NAs species, using novel analytical methods, can be combined with various toxicity methods to assess the efficiency of OSPW treatment processes.

Identification and functional characterization of the goldfish (Carassius auratus L.) high mobility group box 1 (HMGB1) chromatin-binding protein

We report on the identification and functional characterization of HMGB1 of the goldfish. Quantitative analysis indicated the highest expression of goldfish HMGB1 in the brain, with lower mRNA levels in spleen, intestine, kidney, gill and heart. HMGB1 was also differentially expressed in goldfish immune cell populations with highest mRNA levels present in splenocytes and neutrophils. We generated and functionally characterized the recombinant HMGB1 (rgHMGB1). The rgHMGB1 primed the respiratory burst response in monocytes and induced nitric oxide production of primary goldfish macrophages. Treatment of goldfish macrophages with heat-killed Mycobacterium marinum and Aeromonas salmonicida elevated the expression of HMGB1 and resulted in higher HMGB1 protein levels. The rgHMGB1 induced a dose-dependent production of TNFα-2 and IL-1β1 of goldfish macrophages. Furthermore, the dual luciferase reporter assay revealed that goldfish HMGB1 induced the activation of the NF-κB signaling pathway. Our results indicate that goldfish HMGB1 is a critical regulatory cytokine of inflammatory and antimicrobial response of the goldfish.

The analysis of goldfish (Carassius auratus L.) innate immune responses after acute and subchronic exposures to oil sands process-affected water

We examined the immunotoxic effects of acute and subchronic exposures of goldfish to aged, fresh, and ozonated oil sands process-affected water (OSPW) using a flow-through exposure apparatus. We measured the expression of proinflammatory cytokine genes, the antimicrobial responses of primary macrophages isolated from OSPW-exposed fish, and the ability of the goldfish to control infection with a protozoan parasite, Trypanosoma carassii. After acute (1 week) exposure to aged OSPW, we observed upregulation in the expression of interferon gamma (IFN-γ), tumor necrosis factor alpha-2 (TNF-α2) in the kidney and spleen but not in gills of the fish. After subchronic (12 weeks) exposure to aged OSPW, we observed significant increases in mRNA levels of proinflammatory genes in the gill (IFN-γ, interleukin-1 beta 1 [IL1-β1], TNF-α2), kidney (IL1-β1, TNF-α2), and spleen (IL1-β1). An upregulation of immune gene expression in the gill and kidney (IFN-γ, IL1-β1, TNF-α2) and spleen (IL1-β1, TNF-α2) was observed after acute exposure of fish to diluted fresh OSPW. Following subchronic exposure to diluted fresh OSPW, we observed high mRNA levels of IL1-β1 in all tissues examined. However, there were significant decreases in the mRNA levels of IFN-γ and TNF-α2 in the kidney and spleen and gill and spleen (IL-12p35 and IL-12p40) of exposed fish. There were no changes in the expression of anti-inflammatory cytokine IL-10 after both acute and subchronic exposures to diluted fresh OSPW. In fish exposed to ozonated fresh OSPW, immune gene expression was similar to nonexposed control fish in all organs examined, with exception of IL1-β1. The ability of primary kidney macrophages to generate reactive oxygen and nitrogen intermediates was significantly reduced in fish exposed to fresh OSPW. The enhanced proinflammatory response after acute exposure to diluted fresh OSPW was confirmed by the parasite challenge experiments, where OSPW-exposed fish controlled the infection better than nonexposed fish.

IFN-γ-activated lymphocytes boost nitric oxide production in grass carp monocytes/macrophages

It is well known that IFN-γ is a prime activator of nitric oxide (NO) production by monocytes/macrophages in mammals and fish. In parallel, whether IFN-γ-activated lymphocytes are associated with NO production remains unclear. In this study, grass carp monocytes/macrophages and lymphocytes from head kidney were isolated and effects of recombinant grass carp IFN-γ (rgcIFN-γ) on NO releases by these two cell populations were determined. Results showed that rgcIFN-γ time- and dose-dependently increased NO production by monocytes/macrophages but not lymphocytes, which are consistent with the findings in mammals. Interestingly, rgcIFN-γ displayed a greater stimulation on NO production in the co-cultures of monocytes/macrophages and lymphocytes when compared with that in the culture of monocytes/macrophages alone. Furthermore, the media harvested from rgcIFN-γ-treated lymphocytes were effective in boosting NO release in monocytes/macrophages. These data suggest that secretions from rgcIFN-γ-treated lymphocytes may be involved in the NO release by monocytes/macrophages. To address this hypothesis, effect of rgcIFN-γ on the gene expression of inflammatory cytokines in grass carp lymphocytes was examined, showing that it consistently stimulated the mRNA expression of grass carp TNF-α and IL-1β but not IFN-γ. Furthermore, treatment of rgcIFN-γ combined with recombinant grass carp IL-1β (rgcIL-1β) induced a NO production by monocytes/macrophages, which was significantly higher than those induced by either cytokine alone. It provides the evidence that the cytokines secreted by the activated lymphocytes may facilitate the NO production by monocytes/macrophages. Taken together, our findings point out a new mechanism for the involvement of IFN-γ-activated lymphocytes in the NO production by monocytes/macrophages in fish. This knowledge not only strengthens the role of IFN-γ in immune system but also provides the evidence for the existence of a close relationship between lymphocytes and monocytes/macrophages in fish.

TNF receptors regulate vascular homeostasis in zebrafish through a caspase-8, caspase-2 and P53 apoptotic program that bypasses caspase-3

Although it is known that tumor necrosis factor receptor (TNFR) signaling plays a crucial role in vascular integrity and homeostasis, the contribution of each receptor to these processes and the signaling pathway involved are still largely unknown. Here, we show that targeted gene knockdown of TNFRSF1B in zebrafish embryos results in the induction of a caspase-8, caspase-2 and P53-dependent apoptotic program in endothelial cells that bypasses caspase-3. Furthermore, the simultaneous depletion of TNFRSF1A or the activation of NF-κB rescue endothelial cell apoptosis, indicating that a signaling balance between both TNFRs is required for endothelial cell integrity. In endothelial cells, TNFRSF1A signals apoptosis through caspase-8, whereas TNFRSF1B signals survival via NF-κB. Similarly, TNFα promotes the apoptosis of human endothelial cells through TNFRSF1A and triggers caspase-2 and P53 activation. We have identified an evolutionarily conserved apoptotic pathway involved in vascular homeostasis that provides new therapeutic targets for the control of inflammation- and tumor-driven angiogenesis.

The acute and sub-chronic exposures of goldfish to naphthenic acids induce different host defense responses

Naphthenic acids (NAs) are believed to be the major toxic component in oil sands process-affected water (OSPW) produced by the oil sands mining industry in Northern Alberta, Canada. We recently reported that oral exposure to NAs alters mammalian immune responses, but the effect of OSPW or NAs on the immune mechanisms of aquatic organisms has not been fully elucidated. We analyzed the effects of acute and sub-chronic NAs exposures on goldfish immune responses by measuring the expression of three pro-inflammatory cytokine genes, antimicrobial functions of macrophages, and host defense after challenge with a protozoan pathogen (Trypanosoma carassii). One week after NAs exposure, fish exhibited increased expression of pro-inflammatory cytokines (IFNγ, IL-1β1, TNF-α2) in the gills, kidney and spleen. Primary macrophages from fish exposed to NAs for one week, exhibited increased production of nitric oxide and reactive oxygen intermediates. Goldfish exposed for one week to 20 mg/L NAs were more resistant to infection by T. carassii. In contrast, sub-chronic exposure of goldfish (12 weeks) to NAs resulted in decreased expression of pro-inflammatory cytokines in the gills, kidney and spleen. The sub-chronic exposure to NAs reduced the ability of goldfish to control the T. carassii infection, exemplified by a drastic increase in fish mortality and increased blood parasite loads. This is the first report analyzing the effects of OSPW contaminants on the immune system of aquatic vertebrates. We believe that the bioassays depicted in this work will be valuable tools for analyzing the efficacy of OSPW remediation techniques and assessment of diverse environmental pollutants.

Origin and evolution of TNF and TNF receptor superfamilies

The tumor necrosis factor superfamily (TNFSF) and the TNF receptor superfamily (TNFRSF) have an ancient evolutionary origin that can be traced back to single copy genes within Arthropods. In humans, 18 TNFSF and 29 TNFRSF genes have been identified. Evolutionary models account for the increase in gene number primarily through multiple whole genome duplication events as well as by lineage and/or species-specific tandem duplication and translocation. The identification and functional analyses of teleost ligands and receptors provide insight into the critical transition between invertebrates and higher vertebrates. Bioinformatic analyses of fish genomes and EST datasets identify 14 distinct ligand groups, some of which are novel to teleosts, while to date, only limited numbers of receptors have been characterized in fish. The most studied ligand is TNF of which teleost species possess between 1 and 3 copies as well as a receptor similar to TNFR1. Functional studies using zebrafish indicate a conserved role of this ligand-receptor system in the regulation of cell survival and resistance to infectious disease. The increasing interest and use of TNFSF and TNFRSF modulators in human and animal medicine underscores the need to understand the evolutionary origins as well as conserved and novel functions of these biologically important molecules.

Antimicrobial mechanisms of fish leukocytes

Early activation and coordination of innate defenses are critical for effective responses against infiltrating pathogens. Rapid engagement of immune cells provides a critical first line of defense soon after pathogen infiltration. Activation leads to a well-orchestrated set of events that sees the induction and regulation of intracellular and extracellular antimicrobial defenses. An array of regulatory mediators, highly toxic soluble molecules, degradative enzymes and antimicrobial peptides provides maximal protection against a wide range of pathogens while limiting endogenous damage to host tissues. In this review we highlight recent advances in our understanding of innate cellular antimicrobial responses of teleost fish and discuss their implications to cell survival, immunomodulation and death. The evolutionary conservation of these responses is a testament to their effectiveness against pathogen infiltration and their commitment to effective maintenance of host homeostasis. Importantly, recent developments in teleost fish systems have identified novel host defense strategies that may be unique to this lower vertebrate group or may point to previously unknown innate mechanisms that also play a significant role in higher vertebrate host immunity.

Analysis of the antimicrobial responses of primary phagocytes of the goldfish (Carassius auratus L.) against Mycobacterium marinum

The slow growth rate of Mycobacterium spp. that infect humans coupled with a lack of reliable in vitro infection model systems has hindered the progress of research in host cell-mycobacteria interactions. Recent studies have utilized the relatively fast growing Mycobacterium marinum to examine the host-pathogen interface in natural fish hosts. Here we describe the use of primary goldfish monocyte and mature macrophage cultures to investigate the immune cell-M. marinum interactions. Live and heat-killed M. marinum abrogated the recombinant goldfish (rg)TNFα2 and rgIFNγ-induced monocyte reactive oxygen production. Live but not heat-killed M. marinum also ablated rgIFNγrel and rg-TNFα2 induced macrophage nitric oxide production. M. marinum induced significant changes in gene expression of select NADPH oxidase components and inflammatory cytokine receptors and up-regulated the expression of immunosuppressive genes IL-10, TGFβ1 and SOCS-3. The exposure of monocytes and mature macrophages to M. marinum caused an increase in the mRNA levels of several pro-inflammatory genes. Stimulation of monocytes and macrophages with rgTNFα2, rgIFNγ, or rgIFNγrel reduced the survival of intracellular mycobacteria. The characterization of the interaction between M. marinum and natural host-derived primary phagocyte cultures will enable future studies on the host-pathogen interactions in mycobacterial infections.

Innate immune responses and permissiveness to ranavirus infection of peritoneal leukocytes in the frog Xenopus laevis

Ranaviruses such as frog virus 3 ([FV3] family Iridoviridae) are increasingly prevalent pathogens that infect reptiles, amphibians, and fish worldwide. Whereas studies in the frog Xenopus laevis have revealed the critical involvement of CD8 T-cell and antibody responses in host resistance to FV3, little is known about the role played by innate immunity to infection with this virus. We have investigated the occurrence, composition, activation status, and permissiveness to infection of peritoneal leukocytes (PLs) in Xenopus adults during FV3 infection by microscopy, flow cytometry, and reverse transcription-PCR. The total number of PLs and the relative fraction of activated mononucleated macrophage-like cells significantly increase as early as 1 day postinfection (dpi), followed by NK cells at 3 dpi, before the peak of the T-cell response at 6 dpi. FV3 infection also induces a rapid upregulation of proinflammatory genes including arginase 1, interleukin-1beta, and tumor necrosis factor alpha. Although PLs are susceptible to FV3 infection, as evidenced by apoptotic cells, active FV3 transcription, and the detection of viral particles by electron microscopy, the infection is weaker (fewer infectious particles), more transitory, and involves a smaller fraction (less than 1%) of PLs than the kidney, the main site of infection. However, viral DNA remains detectable in PLs for at least 3 weeks postinfection, past the point of viral clearance observed in the kidneys. This suggests that although PLs are actively involved in anti-FV3 immune responses, some of these cells can be permissive and harbor quiescent, asymptomatic FV3.