Characterization and functional analysis of goldfish (Carassius auratus L.) tumor necrosis factor-alpha

Immunosuppressive effects and associated compensatory responses in zebrafish after full life-cycle exposure to environmentally relevant concentrations of cadmium

In natural environments, fish survive in polluted water by cadmium (Cd) throughout their whole life cycle. However, little information is available on Cd toxicity considering a life cycle assessment. The present study investigated effects of environmental levels of cadmium (0, 2.5, and 5μg/L) on immune responses in liver and spleen of zebrafish for 15 weeks, from embryos to sexually maturity. Nitric oxide (NO) levels and iNOS activity declined in liver and spleen of zebrafish exposed to 5μg/L Cd, suggesting an immunosuppressive effect. The result was further supported by the decreased transcriptional levels of proinflammatory cytokines by Cd, such as interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-1β (IL-1β), and tumour necrosis factor-α (TNF-α) in liver. However, a sharp increase in the mRNA levels of these cytokines was observed in spleen of zebrafish exposed to Cd. The increased mRNA expression of these proinflammatory cytokines may be the secondary effect following immunosuppression and just reflect a compensatory mechanism for coping with the decreased immunity, which may explain an increase in mRNA levels and a decrease in iNOS activity in spleen of zebrafish exposed to Cd. In liver, the down-regulated mRNA levels of iNOS paralleled with the decreased iNOS activity, suggesting a synchronous response from a molecular level to a biochemical level. Positive correlations between mRNA expression levels of nuclear transcription factor κB (NF-κB) and proinflammatory cytokines were also observed, suggesting that NF-κB might be required for the protracted induction of inflammatory genes. The corresponding changes in the mRNA levels of the inhibitor of κBα (IκBαa and IκBαb) may form a feedback loop to restore transcriptional activity of NF-κB. Furthermore, splenic ROS levels were increased by 5μg/L Cd, possibly activating NF-κB pathway. Taken together, immunosuppressive effects and tissue-dependent compensatory responses were demonstrated in zebrafish after full life-cycle exposure to environmental levels of Cd, indicating a compromise between survival and immunity.

Protective immunity of grass carp induced by DNA vaccine encoding capsid protein gene (vp7) of grass carp reovirus using bacterial ghost as delivery vehicles

Grass carp reovirus (GCRV) is one of the most pathogenic aquareovirus and can cause lethal hemorrhagic disease in grass carp (Ctenopharyngodon idella). However, management of GCRV infection remains a challenge. Therefore, it is necessary to find effective means for the control of its infection. The uses of bacterial ghost (BG, non-living bacteria) as carriers for DNA delivery have received considerable attentions in veterinary and human vaccines studies. Nevertheless, there is still no report about intramuscular administration of bacterial ghost-based DNA vaccines in fish. In the current study, a novel vaccine based on Escherichia coli DH5α bacterial ghost (DH5α-BG), delivering a major capsid protein gene (vp7) of grass carp reovirus encoded DNA vaccine was developed to enhance the efficacy of a vp7 DNA vaccine against GCRV in grass carp. The grass carp was injected intramuscularly by different treatments -i) naked pcDNA-vp7 (containing plasmid 1, 2.5 and 5 μg, respectively), ii) DH5α-BG/pcDNA-vp7 (containing plasmid 1, 2.5 and 5 μg, respectively) and iii) naked pcDNA, DH5α-BG or phosphate buffered saline. The immune responses and disease resistance of grass carp were assessed in different groups, and results indicated that the antibody levels, serum total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity, acid phosphatase (ACP) activity and alkaline phosphatase (AKP) activity and immune-related genes were significantly enhanced in fish immunized with DH5α-BG/pcDNA-vp7 vaccine (DNA dose ranged from 2.5 to 5 μg). In addition, the relative percentage survival were significantly enhanced in fish immunized with DH5α-BG/pcDNA-vp7 vaccine and the relative percentage survival reached to 90% in DH5α-BG/pcDNA-vp7 group than that of naked pcDNA-vp7 (42.22%) at the highest DNA dose (5 μg) after 14 days of post infection. Moreover, the level of pcDNA-vp7 plasmid was higher in DH5α-BG/pcDNA-vp7 groups than naked pcDNA-vp7 groups in muscle and kidneys tissues after 21 days. Overall, those results suggested that DH5α bacterial ghost based DNA vaccine might be used as a promising vaccine for aquatic animals to fight against GCRV infection.

Identification and Characterization of Lipopolysaccharide Induced TNFα Factor from Blunt Snout Bream, Megalobrama amblycephala

Lipopolysaccharide induced TNFα factor (LITAF) is an important transcription factor responsible for regulation of tumor necrosis factor α. In this study, a novel litaf gene (designated as Malitaf) was identified and characterized from blunt snout bream, Megalobrama amblycephala. The full-length cDNA of Malitaf was of 956 bp, encoding a polypeptide of 161 amino acids with high similarity to other known LITAFs. A phylogenetic tree also showed that Malitaf significantly clustered with those of other teleost, indicating that Malitaf was a new member of fish LITAF family. The putative maLITAF protein possessed a highly conserved LITAF domain with two CXXC motifs. The mRNA transcripts of Malitaf were detected in all examined tissues of healthy M. amblycephala, including kidney, head kidney, muscle, liver, spleen, gill, and heart, and with the highest expression in immune organs: spleen and head kidney. The expression level of Malitaf in spleen was rapidly up-regulated and peaked (1.29-fold, p < 0.05) at 2 h after lipopolysaccharide (LPS) stimulation. Followed the stimulation of Malitaf, Matnfα transcriptional level was also transiently induced to a high level (51.74-fold, p < 0.001) at 4 h after LPS stimulation. Taken together, we have identified a putative fish LITAF ortholog, which was a constitutive and inducible immune response gene involved in M. amblycephala innate immunity during the course of a pathogenic infection.

Preliminary study on the relationship between dexamethasone and pathogen susceptibility on crucian carp (Carassius auratus)

Dexamethasone, a known immunosuppressant, can inhibit the immune response and increase the amount of pathogen in body, but the role of dexamethasone affecting susceptibility of crucian carp (Carassius auratus) to pathogen is unclear. The effects of dexamethasone on susceptibility of crucian carp to Aeromonas hydrophila were investigated in this study. The fish were divided into four groups randomly and injected intraperitoneally by dexamethasone for 0 day (group D), 3 days (group C), 6 days (group B), and 9 days (group A), respectively. The serum lysozyme activity was significantly declined in group A, B and C. Relative immune gene expression such as il-1β, cxcl-8, tnfα and crp in kidney were down-regulation compared to group D. After that crucian carp were infected with A. hydrophila, crucian carp treated by dexamethasone had higher mortality (group A 95%, group B 76%, group C 31%) when compared to group D (4% mortality); the amount of pathogen in was significantly increased (P < 0.05) in liver, kidney and spleen of fish in group A-C compared to group D. These results implicated that higher susceptibility caused by dexamethasone may be induced by the decrease of lysozyme activity and the down-regulation of some immune genes.

Dietary Lactobacillus acidophilus modulated skin mucus protein profile, immune and appetite genes expression in gold fish (Carassius auratus gibelio)

The objective of the present study was to investigate the effect of dietary Lactobacillus acidophilus on skin mucus protein pattern, immune and appetite related genes expression as well as growth performance in gold fish (Carassius auratus gibelio). Three hundred healthy gold fish (2.5 ± 0.05) juveniles were randomly distributed in 12 glass aquariums (400-L; 25 fish per aquaria) and fed experimental diets contain different levels of L. acidophilus (0, 1.5 × 10⁸, 3 × 10⁸ and 6 × 10⁸) for 8 weeks. SDS-PAGE analysis of skin mucus protein profile at the end of the feeding trial revealed differences in protein profile of probiotic fed fish and control group; even three new bands were observed in L. acidophilus treated groups. Furthermore, fish fed 6 × 10⁸ CFU g^-1 supplemented diet showed up-regulation of both TNF-1α and TNF-2α gene expression (P < 0.05). Evaluation of appetite related gene expression showed down-regulation of ghrelin in probiotic fed fish compared those of control treatment (P < 0.05). However, administration of different levels of L. acidophilus had no significant effects on growth performance (P > 0.05). These results demonstrated that while no beneficial effects on growth performance, dietary L. acidophilus affects immune and appetite related genes expression as well as skin mucus protein profile.

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.

The unique myelopoiesis strategy of the amphibian Xenopus laevis

Myeloid progenitors reside within specific hematopoietic organs and commit to progenitor lineages bearing megakaryocyte/erythrocyte (MEP) or granulocyte/macrophage potentials (GMP) within these sites. Unlike other vertebrates, the amphibian Xenopus laevis committed macrophage precursors are absent from the hematopoietic subcapsular liver and instead reside within their bone marrow. Presently, we demonstrate that while these frogs' liver-derived cells are unresponsive to recombinant forms of principal X. laevis macrophage (colony-stimulating factor-1; CSF-1) and granulocyte (CSF-3) growth factors, bone marrow cells cultured with CSF-1 and CSF-3 exhibit respectively archetypal macrophage and granulocyte morphology, gene expression and functionalities. Moreover, we demonstrate that liver, but not bone marrow cells possess erythropoietic capacities when stimulated with a X. laevis erythropoietin. Together, our findings indicate that X. laevis retain their MEP within the hematopoietic liver while sequestering their GMP to the bone marrow, thus marking a very novel myelopoietic strategy as compared to those seen in other jawed vertebrate species.

TNF-α is involved in apoptosis triggered by grass carp reovirus infection in vitro

Grass carp reovirus (GCRV) infection causes apoptosis in Ctenopharyngodon idella kidney cells (CIK). However, the cause of GCRV-induced apoptosis and its signaling pathways remain unknown. This study investigated the role of TNF-α-induced capase-8 pathways in mediating GCRV-induced apoptosis in the grass carp (Ctenopharyngodon idella). Recombinant TNF-α was expressed and purified from Escherichia. coli. The western blot assay indicated that TNF-α expression level in kidney and spleen was higher than that in liver. In apoptosis assay, recombinant TNF-α triggered significant apoptosis in CIK cells, which was characterized by increased mRNA levels of TNF-α, TRADD or caspase-8, and enhanced caspase-8 activity in CIK cells. To confirm the biological activity of TNF-α during GCRV infection, significant apoptosis in CIK cells was induced by GCRV correlating with enhanced caspase-8 activity, increased mRNA level of TNF-α, TRADD or caspase-8, increased protein level of TNF-α in CIK cells and cell supernatant, suggesting that TNF-α-induced capase-8 pathways might be involved in GCRV-triggered apoptosis. Furthermore, treatment with an anti-TNF-α polyclonal antibody significantly decreased the degree of apoptosis in infected CIK cells compared with cells treated with a control antibody, which confirmed that TNF-α was a key mediator involved in GCRV-induced apoptosis. Taken together, these results indicated that GCRV might trigger apoptosis via TNF-α induced capase-8 pathways in CIK cells.

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.

Carp Il10 Has Anti-Inflammatory Activities on Phagocytes, Promotes Proliferation of Memory T Cells, and Regulates B Cell Differentiation and Antibody Secretion

In the current study, we investigated the effects of carp Il10 on phagocytes and lymphocytes. Carp Il10 shares several prototypical inhibitory activities on phagocytes with mammalian IL-10, including deactivation of neutrophils and macrophages, as shown by inhibition of oxygen and nitrogen radical production, as well as reduced expression of proinflammatory genes and mhc genes involved in Ag presentation. Similar to mammalian IL-10, carp Il10 acts through a signaling pathway involving phosphorylation of Stat3, ultimately leading to the early upregulation of socs3 expression. To our knowledge, this is the first study of the effects of Il10 on lymphocytes in fish. Although Il10 did not affect survival and proliferation of T cells from naive animals, it greatly promoted survival and proliferation of T cells in cultures from immunized animals, but only when used in combination with the immunizing Ag. Preliminary gene expression analysis suggests that, under these circumstances, carp Il10 stimulates a subset of CD8+ memory T cells while downregulating CD4+ memory Th1 and Th2 responses. In addition to the regulatory effect on T cells, carp Il10 stimulates proliferation, differentiation, and Ab secretion by IgM+ B cells. Overall, carp Il10 shares several prototypical activities with mammalian IL-10, including downregulation of the inflammatory response of phagocytes, stimulation of proliferation of subsets of memory T lymphocytes, and proliferation, differentiation, and Ab secretion by IgM+ B lymphocytes. To our knowledge, this is the first comprehensive analysis of biological activities of fish Il10 on both phagocytes and lymphocytes showing functional conservation of several properties of Il10.

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.

Development of an in vitro model system to study the interactions between Mycobacterium marinum and teleost neutrophils

The lack of a reliable mammalian neutrophil in vitro culture system has restricted our ability to examine their precise roles in mycobacterial infections. Previously, we developed the procedures for the isolation and culture of primary kidney-derived neutrophil-like cells from goldfish that are functionally and morphologically similar to mammalian neutrophils. The cultured primary goldfish neutrophils exhibited prolonged viability and functional effector responses. In this study, we demonstrate that when exposed to live or heat-killed Mycobacterium marinum, goldfish neutrophils increased their mRNA levels for several pro-inflammatory cytokines (il-1β1, il-1β2, tnfα-1, tnfα-2) and the cytokine receptors (ifngr1-1, tnfr1, tnfr2). These neutrophils also exhibited chemotaxis toward live mycobacteria, internalized the bacilli, and produced reactive oxygen intermediates (ROI) in response to pathogen exposure. The survival of intracellular mycobacteria was significantly reduced in activated neutrophils, indicating a robust killing response by these teleost granulocytes. We suggest that this goldfish primary neutrophil in vitro model system will provide important information regarding neutrophil-mediated host defense mechanisms against mycobacteria in teleosts as well as in higher vertebrates.

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.

Along the Axis between Type 1 and Type 2 Immunity; Principles Conserved in Evolution from Fish to Mammals

A phenomenon already discovered more than 25 years ago is the possibility of naïve helper T cells to polarize into TH1 or TH2 populations. In a simplified model, these polarizations occur at opposite ends of an "immune 1-2 axis" (i1-i2 axis) of possible conditions. Additional polarizations of helper/regulatory T cells were discovered later, such as for example TH17 and Treg phenotypes; although these polarizations are not selected by the axis-end conditions, they are affected by i1-i2 axis factors, and may retain more potential for change than the relatively stable TH1 and TH2 phenotypes. I1-i2 axis conditions are also relevant for polarizations of other types of leukocytes, such as for example macrophages. Tissue milieus with "type 1 immunity" ("i1") are biased towards cell-mediated cytotoxicity, while the term "type 2 immunity" ("i2") is used for a variety of conditions which have in common that they inhibit type 1 immunity. The immune milieus of some tissues, like the gills in fish and the uterus in pregnant mammals, probably are skewed towards type 2 immunity. An i2-skewed milieu is also created by many tumors, which allows them to escape eradication by type 1 immunity. In this review we compare a number of i1-i2 axis factors between fish and mammals, and conclude that several principles of the i1-i2 axis system seem to be ancient and shared between all classes of jawed vertebrates. Furthermore, the present study is the first to identify a canonical TH2 cytokine locus in a bony fish, namely spotted gar, in the sense that it includes RAD50 and bona fide genes of both IL-4/13 and IL-3/ IL-5/GM-CSF families.

Neutrophil Development, Migration, and Function in Teleost Fish

It is now widely recognized that neutrophils are sophisticated cells that are critical to host defense and the maintenance of homeostasis. In addition, concepts such as neutrophil plasticity are helping to define the range of phenotypic profiles available to cells in this group and the physiological conditions that contribute to their differentiation. Herein, we discuss key features of the life of a teleost neutrophil including their development, migration to an inflammatory site, and contributions to pathogen killing and the control of acute inflammation. The potent anti-microbial mechanisms elicited by these cells in bony fish are a testament to their long-standing evolutionary contributions in host defense. In addition, recent insights into their active roles in the control of inflammation prior to induction of apoptosis highlight their importance to the maintenance of host integrity in these early vertebrates. Overall, our goal is to summarize recent progress in our understanding of this cell type in teleost fish, and to provide evolutionary context for the contributions of this hematopoietic lineage in host defense and an efficient return to homeostasis following injury or infection.

Immunohistochemical detection and gene expression of TNFα in turbot (Scophthalmus maximus) enteromyxosis

Enteromyxum scophthalmi (Myxozoa) constitutes one of the most devastating pathogens for turbot (Scophthalmus maximus, L.) aquaculture. This parasite causes a severe intestinal parasitosis that leads to a cachectic syndrome with high morbidity and mortality rates for which no therapeutic options are available. Presence of inflammatory infiltrates, increased apoptotic rates and epithelial detaching have been described at intestinal level, as well as leukocyte depletion in lymphohaematopoietic organs. Previous investigations on enteromyxosis in turbot showed the high susceptibility of this species to the parasite and reported the existence of a dysregulated immune response against the parasite. The pleiotropic cytokine tumour necrosis factor alpha (TNFα) plays a major role in immune response and is involved in a wide range of biological activities. In teleost, the gene expression of this cytokine has been found regulated under several pathological conditions. Teleost TNFα shows some analogous functions with its mammalian counterparts, but the extent of its activities is still poorly understood. Cytokines are generally considered as a double-edge sword and TNFα has been implicated in the pathogenesis of different inflammatory diseases as well as in wasting syndromes described in mammals. The aim of this work was to analyse the expression of TNFα during enteromyxosis with molecular (Q-PCR) and morphological (immunohistochemistry) tools. Kidney, spleen and pyloric caeca from turbot with moderate and severe infections were analysed and compared to healthy naïve fish. TNFα expression was increased in both spleen and kidney in the earlier stages of the disease, whereas in severely infected fish, the expression decreased, especially in kidney. At the intestinal level, an increase in the number of TNFα-positive cells was noticed, which was proportional to the infiltration of inflammatory cells. The results demonstrate the involvement of TNFα in the immune response to E. scophthalmi in turbot, which could be related to the development of the clinic signs and lesions.

Neutrophil contributions to the induction and regulation of the acute inflammatory response in teleost fish

Neutrophils are essential to the acute inflammatory response, where they serve as the first line of defense against infiltrating pathogens. We report that, on receiving the necessary signals, teleost (Carassius auratus) neutrophils leave the hematopoietic kidney, enter into the circulation, and dominate the initial influx of cells into a site of inflammation. Unlike mammals, teleost neutrophils represent <5% of circulating leukocytes during periods of homeostasis. However, this increases to nearly 50% immediately after intraperitoneal challenge with zymosan, identifying a period of neutrophilia that precedes the peak influx of neutrophils into the challenge site at 18 h after injection). We demonstrate that neutrophils at the site of inflammation alter their phenotype throughout the acute inflammatory response, and contribute to both the induction and the resolution of inflammation. However, neutrophils isolated during the proinflammatory phase (18 h after injection) produced robust respiratory burst responses, released inflammation-associated leukotriene B(4), and induced macrophages to increase reactive oxygen species production. In contrast, neutrophils isolated at 48 h after infection (proresolving phase) displayed low levels of reactive oxygen species, released the proresolving lipid mediator lipoxin A(4), and downregulated reactive oxygen species production in macrophages before the initiation of apoptosis. Lipoxin A(4) was a significant contributor to the uptake of apoptotic cells by teleost macrophages and also played a role, at least in part, in the downregulation of macrophage reactive oxygen species production. Our results highlight the contributions of neutrophils to both the promotion and the regulation of teleost fish inflammation and provide added context for the evolution of this hematopoietic lineage.

Immunolocalization of tumor necrosis factor alpha in turbot (Scophthalmus maximus, L.) tissues

Tumor necrosis factor alpha (TNFα) is a cytokine involved in a broad spectrum of cellular and organismal responses. Its main function, as a potent pro-inflammatory mediator, has been demonstrated in numerous teleost species and there are many reports on the modulation of TNFα gene expression under pathological conditions. Nevertheless, there is still scarce knowledge about the tissue distribution and type of cells that express this cytokine in fish species, which would help to further investigate its biological activities. These studies are hampered by the lack of molecular markers for teleost that hinder the development of morphological techniques, like immunohistochemistry. The aim of this work was to develop an immunohistochemical technique for the detection of TNFα in paraffin-embedded organs from healthy turbot (Scophthalmus maximus), an economically-important marine fish species. A commercial anti-human TNFα antibody, whose specificity was confirmed by western blot analysis, was used. Immunoreactive cells were observed in higher numbers in the lymphohematopoietic organs, kidney, spleen and thymus, although TNFα-positive cells were also present in the digestive tract, liver, heart, gills and skin. Similarly to non-fish species, monocytes/macrophages appeared to be the main producers of this cytokine; nevertheless, the presence of immunoreactive rodlet cells in different tissues was also reported. The nature and distribution of the labeled cells appeared to be related with a strategic localization for defense response to antigenic challenge. The relative abundance of TNFα-positive cells in the lymphohematopoietic organs also suggests that this cytokine may have a broader role in the normal physiology of those organs. The immunohistochemical technique allowed the in-situ characterization of TNFα expression, representing a valid tool to investigate the immune response of turbot.

Dual-parallel inhibition of IL-10 and TGF-β1 controls LPS-induced inflammatory response via NF-κB signaling in grass carp monocytes/macrophages

In fish, the knowledge on the regulation of inflammatory responses is limited. In the present study, LPS rapidly increased the mRNA levels of grass carp pro-inflammatory factors, including tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), inducible nitric oxides synthase (iNOS) and IL-8 in monocytes/macrophages, indicating the occurrence of innate inflammatory responses in fish as seen in mammals. Intriguingly, the gene expression and protein secretion of grass carp IL-10 (gcIL-10) and TGF-β1 (gcTGF-β1) were induced by LPS in the same cell model, promoting us to clarify their roles in regulating inflammatory response. Results revealed that grass carp IL-10 polyclonal antibody (anti-gcIL-10 pAb) and grass carp TGF-β1 monoclonal antibody (anti-gcTGF-β1 mAb) could amplify the stimulation of LPS on the mRNA levels of tnfα, il1β, inos and il8, suggesting the inhibitory tone of endogenous IL-10 and TGF-β1 in LPS-challenged immune responses. This notion was further supported by the fact that recombinant grass carp IL-10 (rgcIL-10) and recombinant grass carp TGF-β1 (rgcTGF-β1) attenuated LPS-stimulated tnfα, il1β, inos and il8 gene expression in monocytes/macrophages. Further study revealed that rgcIL-10 and rgcTGF-β1 impaired NF-κB activation by blocking LPS-induced grass carp IκBα (gcIκBα) protein degradation in the cells. In addition, the correlation between gcIL-10 and gcTGF-β1 in this regulation was examined by immunoneutralization, unveiling that anti-gcTGF-β1 mAb and anti-gcIL-10 pAb were unable to alter the inhibitory effects of rgcIL-10 and rgcTGF-β1 on pro-inflammatory factors expression in grass carp monocytes/macrophages, respectively. This dual and parallel effect of gcIL-10 and gcTGF-β1 strengthened their importance in controlling inflammatory responses. Taken together, our findings shed a light on the functional role, regulatory mechanism and relationship of fish IL-10 and TGF-β1 in regulating inflammatory response.

Teleost soluble CSF-1R modulates cytokine profiles at an inflammatory site, and inhibits neutrophil chemotaxis, phagocytosis, and bacterial killing

Soluble colony stimulating factor-1 receptor (sCSF-1R) is a novel bony fish protein that contributes to the regulation of macrophage proliferation. We recently showed that this soluble receptor is highly upregulated by teleost macrophages in the presence of apoptotic cells. Further, recombinant sCSF-1R inhibited leukocyte infiltration into a challenge site in vivo. Herein, we characterized the mechanisms underlying these changes as a platform to better understand the evolutionary origins of the CSF-1 immune-regulatory axis and inflammation control in teleosts. Using an in vivo model of self-resolving peritonitis, we show that sCSF-1R downregulates chemokine expression and inhibits neutrophil chemotaxis. Soluble CSF-1R also inhibited gene expression of several pro-inflammatory cytokines and promoted the expression of an anti-inflammatory mediator, IL-10. Finally, the phenotype of infiltrating neutrophils changed significantly in the presence of sCSF-1R. Both a reduced capacity for phagocytosis and pathogen killing were observed. Overall, our results implicate sCSF-1R as an important regulator of neutrophil responses in teleosts. It remains unclear whether this represents an inflammation regulatory factor that is unique to this animal group or one that may be evolutionarily conserved and continues to contribute to the regulation of antimicrobial processes at inflammatory sites in higher vertebrates.

Evolutionary evidence of tumor necrosis factor super family members in the Japanese pufferfish (Takifugu rubripes): Comprehensive genomic identification and expression analysis

Tumor necrosis factor (TNF) and its superfamily (TNFSF) members are important inflammatory cytokines. Although fish have fourteen TNFSF genes, their genomic location and existence are yet to be described and confirmed in the Japanese pufferfish (Fugu) (Takifugu rubripes). Therefore, we conducted in silico identification, synteny analysis of TNFSF genes from Fugu with that of zebrafish and human TNFSF loci and their expression analysis in various tissues. We identified ten novel TNFSF genes, viz. TNFSF5 (CD40L), TNFSF6 (FasL), three TNFSF10 (TRAIL) (-1, 2 and 3), TNFSF11 (RANKlg), TNFSF12 (TWEAK), two TNFSF13B (BAFF) (1 and 2) and TNFSF14 (LIGHT) belonging to seven TNFSFs in Fugu. Several features such as existence of TNF family signature, conservation of genes in TNF loci with human and zebrafish chromosomes and phylogenetic clustering with other teleost TNFSF orthologs confirmed their identity. Fugu TNFSF genes were constitutively expressed in all eight different tissues with most of them expressed highly in liver. Fugu TNFSF10 gene has three homologs present on chromosomes 10 (TNFSF10-1), 8 (TNFSF10-2) and 2 (TNFSF10-3). Moreover, a phylogenetic analysis containing all available vertebrate (mammals, birds, reptiles, amphibians and fish) TNFSF10 orthologs showed that Fugu TNFSF10-1 and 10-3 are present in all vertebrates, whereas TNFSF10-2 was not related to any mammalian and avian orthologs. Viral double-stranded RNA mimic poly (I:C) caused an elevated expression of three Fugu TNFSF10 genes in head kidney cells at 4h indicating probable role of these genes to induce apoptosis in virus-infected cells. In conclusion, Fugu possesses genes belonging to nine TNFSFs including the newly identified seven and previously reported two, TNFSF New (TNF-N) and TNFSF2 (TNF-α). Our findings would add up information to TNFSF evolution among vertebrates.

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.

Antimicrobial responses of teleost phagocytes and innate immune evasion strategies of intracellular bacteria

During infection, macrophage lineage cells eliminate infiltrating pathogens through a battery of antimicrobial responses, where the efficacy of these innate immune responses is pivotal to immunological outcomes. Not surprisingly, many intracellular pathogens have evolved mechanisms to overcome macrophage defenses, using these immune cells as residences and dissemination strategies. With pathogenic infections causing increasing detriments to both aquacultural and wild fish populations, it is imperative to garner greater understanding of fish phagocyte antimicrobial responses and the mechanisms by which aquatic pathogens are able to overcome these teleost macrophage barriers. Insights into the regulation of macrophage immunity of bony fish species will lend to the development of more effective aquacultural prophylaxis as well as broadening our understanding of the evolution of these immune processes. Accordingly, this review focuses on recent advances in the understanding of teleost macrophage antimicrobial responses and the strategies by which intracellular fish pathogens are able to avoid being killed by phagocytes, with a focus on Mycobacterium marinum.

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.

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.

Effects of praziquantel and sanguinarine on expression of immune genes and susceptibility to Aeromonas hydrophila in goldfish (Carassius auratus) infected with Dactylogyrus intermedius

Praziquantel and sanguinarine have been demonstrated positive therapeutic effects on monogenean Dactylogyrus intermedius; however, few studies have considered the post impacts of these antiparasitic chemicals on host after repelling the parasites. The changes of expression of selected immune genes (CCL-1, CXCL-8, IL-1β-1, IL-1β-2, TNFα-1, TNFα-2 and TGF-β) in gill, kidney and spleen and bacterial loads of Aeromonas hydrophila in gill, kidney, spleen and liver following bath administration of these antiparasitic chemicals were evaluated. The results showed that praziquantel and sanguinarine up-regulated to varying degrees of CXCL-8, IL-1β-1, IL-1β-2, TNFα-1 and TNFα-2 in gill, kidney and spleen. They both decreased the CCL-1 expression in gill while increased it in kidney and spleen. However, in all the tested tissues, the expression of TGF-β decreased in praziquantel treated goldfish whereas that increased in sanguinarine treated goldfish. The A. hydrophila challenge test showed that the praziquantel treatment enhanced the susceptibility to A. hydrophila while sanguinarine treatment decreased the susceptibility, as compared with the non-treated group. Overall, the results indicate that bath administration of praziquantel and sanguinarine modulates the immune related genes in goldfish and these may, to some extent, affect their ability to resist bacterial pathogens.

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.

Analysis of the immune response in infections of the goldfish (Carassius auratus L.) with Mycobacterium marinum

The rapid doubling time and genetic relatedness of the fish pathogen Mycobacterium marinum to Mycobacterium tuberculosis has rendered the former an attractive model for investigating mycobacterial host-pathogen interactions. We employed the M. marinum-goldfish infection model to investigate the in vivo immune responses to this pathogen in the context of a natural host. Histological analysis revealed mycobacterial infiltrates in goldfish kidney and spleen tissues, peaking 28 days post infections (dpi). Quantitative gene expression analysis showed significant increases of mRNA levels of pro-inflammatory cytokines (IFNγ, IL-12p40, IL-1β1) and cytokine receptors (IFNGR1-1, TNFR2) at 7 dpi. Conversely, the gene expression levels of key anti-inflammatory cytokines TGFβ and IL-10 were elevated at 14 dpi. Furthermore, M. marinum infections markedly increased the cytokine-primed oxidative burst responses of isolated kidney phagocytes at 7 but not 56 dpi. We believe that the M. marinum-goldfish infection model will be invaluable in furthering the understanding of the mycobacterium host-pathogen interface.

The bioactivity of teleost IL-6: IL-6 protein in orange-spotted grouper (Epinephelus coioides) induces Th2 cell differentiation pathway and antibody production

Interleukin 6 (IL-6) is a protein secreted by T cells and macrophages and plays an important role in immune response. IL-6 regulates the proliferation and differentiation of T cells, and elicits immunoglobulin production in B cells. In this study, the cDNA il-6 (gil-6) sequence of the orange spotted grouper (Epinephelus coioides) was obtained. The deduced IL-6 (gIL-6) protein comprised 223 amino acids, the sequence shared approximately 30% similarity with mammalian IL-6, and between 47% and 69% similarity with other available teleost IL-6. The protein comprises the signal peptide, the IL-6 family signature, and conserved amino acid residues found in IL-6 sequences of other teleost. In order to understand the bioactivity and influence of gIL-6 on humoral immune response, recombinant gIL-6 (rgIL-6) synthesized by prokaryotes was injected into orange spotted groupers, and the immune-related gene expression at various times in various organs was observed. Our results revealed that the Th1 specific transcription factor t-bet was down-regulated and Th2 specific transcription factors gata3, and c-maf were up-regulated in immune organs, following IL-6 stimulation. Additionally, higher levels of igm mRNA and translated protein were detected in rgIL-6 stimulated fish. These results indicate that IL-6 in groupers regulates the differentiation of naїve T helper cells into Th2 cells and elicits the production of antibodies.

Susceptibility of Xenopus laevis tadpoles to infection by the ranavirus Frog-Virus 3 correlates with a reduced and delayed innate immune response in comparison with adult frogs

Xenopus laevis adults mount effective immune responses to ranavirus Frog Virus 3 (FV3) infections and clear the pathogen within 2-3 weeks. In contrast, most tadpoles cannot clear FV3 and succumb to infections within a month. While larval susceptibility has been attributed to ineffective adaptive immunity, the contribution of innate immune components has not been addressed. Accordingly, we performed a comprehensive gene expression analysis on FV3-infected tadpoles and adults. In comparison to adults, leukocytes and tissues of infected tadpoles exhibited modest (10-100 time lower than adult) and delayed (3 day later than adult) increase in expression of inflammation-associated (TNF-α, IL-1β and IFN-γ) and antiviral (Mx1) genes. In contrast, these genes were readily and robustly upregulated in tadpoles upon bacterial stimulation. Furthermore, greater proportions of larval than adult PLs were infected by FV3. Our study suggests that tadpole susceptibility to FV3 infection is partially due to poor virus-elicited innate immune responses.

Immune evasion strategies of ranaviruses and innate immune responses to these emerging pathogens

Ranaviruses (RV, Iridoviridae) are large double-stranded DNA viruses that infect fish, amphibians and reptiles. For ecological and commercial reasons, considerable attention has been drawn to the increasing prevalence of ranaviral infections of wild populations and in aquacultural settings. Importantly, RVs appear to be capable of crossing species barriers of numerous poikilotherms, suggesting that these pathogens possess a broad host range and potent immune evasion mechanisms. Indeed, while some of the 95–100 predicted ranavirus genes encode putative evasion proteins (e.g., vIFα, vCARD), roughly two-thirds of them do not share significant sequence identity with known viral or eukaryotic genes. Accordingly, the investigation of ranaviral virulence and immune evasion strategies is promising for elucidating potential antiviral targets. In this regard, recombination-based technologies are being employed to knock out gene candidates in the best-characterized RV member, Frog Virus (FV3). Concurrently, by using animal infection models with extensively characterized immune systems, such as the African clawed frog, Xenopus laevis, it is becoming evident that components of innate immunity are at the forefront of virus-host interactions. For example, cells of the macrophage lineage represent important combatants of RV infections while themselves serving as targets for viral infection, maintenance and possibly dissemination. This review focuses on the recent advances in the understanding of the RV immune evasion strategies with emphasis on the roles of the innate immune system in ranaviral infections.

TGF-β1 exerts opposing effects on grass carp leukocytes: implication in teleost immunity, receptor signaling and potential self-regulatory mechanisms

In fish immunity, the regulatory role of transforming growth factor-β1 (TGF-β1) has not been fully characterized. Here we examined the immunoregulatory effects of TGF-β1 in grass carp peripheral blood leukocytes (PBL) and head kidney leukocytes (HKL). It is interesting that TGF-β1 consistently stimulated the cell viability and the mRNA levels of pro-inflammatory cytokines (Tnfα and Ifnγ) and T/B cell markers [Cd4-like (Cd4l), Cd8α, Cd8β and Igμ] in PBL, which contrasted with its inhibitory tone in HKL. Further studies showed that grass carp TGF-β1 type I receptor, activin receptor-like kinase 5 (ALK5), was indispensable for the immunoregulatory effects of TGF-β1 in PBL and HKL. Notably, TGF-β1 persistently attenuated ALK5 expression, whereas immunoneutralization of endogenous grass carp TGF-β1 could increase ALK5 mRNA and protein levels. It is consistent with the observation that TGF-β1 decreased the number of ALK5(+) leukocytes in PBL and HKL, revealing a negative regulation of TGF-β1 signaling at the receptor level. Moreover, transient treatment with TGF-β1 for 24 h was sufficient to induce similar cellular responses compared with the continuous treatment. This indicated a possible mechanism by which TGF-β1 triggered the down-regulation of ALK5 mRNA and protein, leading to the desensitization of grass carp leukocytes toward TGF-β1. Accordingly, our data revealed a dual role of TGF-β1 in teleost immunity in which it can serve as a positive or negative control device and provided additional mechanistic insights as to how TGF-β1 controls its signaling in vertebrate leukocytes.

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.

Identification and molecular characterization of the interleukin-10 receptor 1 of the zebrafish (Danio rerio) and the goldfish (Carassius auratus L.)

This is the first report of the identification and molecular characterization of an interleukin-10 receptor 1 in bony fish. By gene synteny analysis, we identified the zebrafish interleukin-10 receptor 1 (IL10R1) and using this IL10R1 sequence, we cloned the goldfish IL10R1 cDNA transcript. The identified fish IL10R1 protein sequences had a putative JAK1 binding site, only one of the two STAT3 binding sites, that are present in all other vertebrates IL10R1 proteins as well as C-terminal serine rich areas, believed to be responsible for the anti-inflammatory properties of IL10R1. Phylogenetically, the fish IL10R1 proteins grouped independently of the amphibian, avian and mammalian IL10R1s. Quantitative gene expression analysis of the IL10R1 of zebrafish and goldfish revealed highest mRNA levels in the spleen tissues. High mRNA levels were also observed in the zebrafish muscle in contrast to low mRNA levels in the muscle of the goldfish. Moderate IL10R1 mRNA levels were seen in most other tissues examined and lowest gene expression was in the liver of both fish species. Goldfish monocytes stimulated with a recombinant goldfish interleukin-10 (rgIL-10) or with heat killed fish pathogens, Aeromonas salmonicida or Trypanosoma carassii, exhibited significantly reduced mRNA levels of the IL10R1. Furthermore, we produced a recombinant form of the goldfish IL10R1 (rgIL10R1) and using in vitro binding studies, demonstrated that the dimerized rgIL-10 specifically interacted with rgIL10R1. Our results suggest that interleukin-10 system has been highly conserved throughout evolution.

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.

Heterogeneity of macrophage activation in fish

In this review, we focus on four different activation states of fish macrophages. In vitro, stimulation with microbial ligands induces the development of innate activated macrophages whereas classically activated macrophages can be induced by stimulation with LPS in combination with (recombinant) IFNγ. Both types of macrophages show elevated phagocytic activity, expression of pro-inflammatory cytokine genes and radical production. Alternatively activated macrophages require the cytokines IL-4/IL-13 for induction of, among others, arginase activity. Until in vitro studies identify the effects of putative IL-4 and IL-13 homologues on fish macrophages, arginase enzyme activity remains the most reliable marker for the presence of alternatively activated macrophages in fish. The best evidence for the existence of regulatory macrophages, associated with the presence of IL-10, comes from in vivo studies, for example during parasitic infections of carp. Altogether, differentially activated macrophages in fish largely resemble the phenotypes of mammalian macrophages. However, the presence of fish-specific ligand recognition by TLRs and of duplicated genes coding for proteins with particular activities, poses additional challenges for the characterization of phenotype-specific gene signatures and cell surface markers.

Fish T cells: recent advances through genomics

This brief review is intended to provide a concise overview of the current literature concerning T cells, advances in identifying distinct T cell functional subsets, and in distinguishing effector cells from memory cells. We compare and contrast a wealth of recent progress made in T cell immunology of teleost, elasmobranch, and agnathan fish, to knowledge derived from mammalian T cell studies. From genome studies, fish clearly have most components associated with T cell function and we can speculate on the presence of putative T cell subsets, and the ability to detect their differentiation to form memory cells. Some recombinant proteins for T cell associated cytokines and antibodies for T cell surface receptors have been generated that will facilitate studying the functional roles of teleost T cells during immune responses. Although there is still a long way to go, major advances have occurred in recent years for investigating T cell responses, thus phenotypic and functional characterization is on the near horizon.

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.

Flow cytometry assays of respiratory burst in Atlantic salmon (Salmo salar L.) and in Atlantic cod (Gadus morhua L.) leucocytes

The oxidation of dihydrorhodamine 123 (DHR) to the fluorescent rhodamine 123 (RHO) was detected using flow cytometry. This assay for detection of respiratory burst activity was established in peripheral blood leucocytes (PBL) and head kidney leucocytes (HKL) of Atlantic salmon and Atlantic cod. The leucocytes were stimulated by phorbol 12-myristate 13-acetate (PMA). For cod cells 10 times lower concentration of PMA had to be used compared to salmon cells, as higher concentrations were toxic and resulted in considerable cell death. The cells found to be RHO-positive were monocytes/macrophages and neutrophils based on the scatter dot plots, but for salmon also some small cells were found to have high fluorescence intensity both in the flow cytometry analyses and by fluorescence microscopy of cytospin preparations. The nature of these cells is not known. For cod leucocytes, such cells were not obvious. The instrument settings are a bit more demanding for cod, as cod cells die more easily compared to salmon cells. In both assays the limit between negative and positive cells has to be carefully considered. The presented flow cytometry protocols for measurements of respiratory burst in salmon and cod leucocytes can be applied in various studies where respiratory burst functions are involved, such as to verify if it is activated or suppressed in connection with infections and immunostimulation.