Molecular and functional characterization of carp TNF: a link between TNF polymorphism and trypanotolerance?

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

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

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

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

Transcriptome analysis provides novel insights into the immune mechanisms of Macrobrachium nipponense during molting

Molting is a basic physiological behavior of the Oriental river prawn (Macrobrachium nipponense), however, the gene expression patterns and immune mechanisms during the molting process of Oriental river prawn are unclear. In the current study, the gene expression levels of the hepatopancreas of the Oriental river prawn at different molting stages (pre-molting, Prm; mid-molting, Mm; and post-molting, Pom) were detected by mRNA sequencing. A total of 1721, 551, and 1054 differentially expressed genes (DEGs) were identified between the Prm hepatopancreas (PrmHe) and Mm hepatopancreas (MmHe), MmHe and Pom hepatopancreas (PomHe) and PrmHe and PomHe, respectively. The results showed that a total of 1151 DEGs were annotated into 316 signaling pathways, and the significantly enriched immune-related pathways were "Lysosome", "Hippo signaling pathway", "Apoptosis", "Autophagy-animal", and "Endocytosis". The qRT-PCR verification results of 30 randomly selected DEGs were consistent with RNA-seq. The expression patterns of eight immune related genes in different molting stages of the Oriental river prawn were analyzed by qRT-PCR. The function of Caspase-1 (CASP1) was further investigated by bioinformatics, qRT-PCR, and RNAi analysis. CASP1 has two identical conserved domains: histidine active site and pentapeptide motif, and the expression of CASP1 is the highest in ovary. The expression levels of triosephosphate isomerase (TPI), Cathepsin B (CTSB) and Hexokinase (HXK) were evaluated after knockdown of CASP1. This research provides a valuable basis to improve our understanding the immune mechanisms of Oriental river prawns at different molting stages. The identification of immune-related genes is of great significance for enhancing the immunity of the Oriental river prawn, or other crustaceans, by transgenic methods in the future.

Cytokines Studied in Carp (Cyprinus carpio L.) in Response to Important Diseases

Cytokines belong to the most widely studied group of intracellular molecules involved in the function of the immune system. Their secretion is induced by various infectious stimuli. Cytokine release by host cells has been extensively used as a powerful tool for studying immune reactions in the early stages of viral and bacterial infections. Recently, research attention has shifted to the investigation of cytokine responses using mRNA expression, an essential mechanism related to pathogenic and nonpathogenic-immune stimulants in fish. This review represents the current knowledge of cytokine responses to infectious diseases in the common carp (Cyprinus carpio L.). Given the paucity of literature on cytokine responses to many infections in carp, only select viral diseases, such as koi herpesvirus disease (KHVD), spring viremia of carp (SVC), and carp edema virus disease (CEVD), are discussed. Aeromonas hydrophila is one of the most studied bacterial pathogens associated with cytokine responses in common carp. Therefore, the cytokine-based immunoreactivity raised by this specific bacterial pathogen is also highlighted in this review.

Euglenozoa: taxonomy, diversity and ecology, symbioses and viruses

Euglenozoa is a species-rich group of protists, which have extremely diverse lifestyles and a range of features that distinguish them from other eukaryotes. They are composed of free-living and parasitic kinetoplastids, mostly free-living diplonemids, heterotrophic and photosynthetic euglenids, as well as deep-sea symbiontids. Although they form a well-supported monophyletic group, these morphologically rather distinct groups are almost never treated together in a comparative manner, as attempted here. We present an updated taxonomy, complemented by photos of representative species, with notes on diversity, distribution and biology of euglenozoans. For kinetoplastids, we propose a significantly modified taxonomy that reflects the latest findings. Finally, we summarize what is known about viruses infecting euglenozoans, as well as their relationships with ecto- and endosymbiotic bacteria.

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.

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

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

Signal Transduction for TNFα-Induced Type II SOCS Expression and Its Functional Implication in Growth Hormone Resistance in Carp Hepatocytes

In mammals, local production of tumor necrosis factor α (TNFα) inhibits growth hormone (GH)-induced IGF-I expression at tissue level and contributes to GH resistance caused by sepsis/endotoxemia and inflammation. Although the loss of GH responsiveness can be mediated by a parallel rise in SOCS expression, the signaling mechanisms for TNFα-induced SOCS expression at the hepatic level have not been characterized and the comparative aspects of the phenomenon, especially in lower vertebrates, are still unknown. Recently, type II SOCS, including SOCS1-3 and CISH, have been cloned in grass carp and shown to act as the feedback repressors for GH signaling via JAK₂/STAT₅ pathway. To shed light on the mechanisms for TNFα-induced GH resistance in fish model, grass carp TNFα was cloned and confirmed to be a single-copy gene expressed in various tissues including the liver. In carp hepatocytes, incubation with the endotoxin LPS induced TNFα expression with parallel rises in SOCS1-3 and CISH mRNA levels. Similar to LPS, TNFα treatment could block GH-induced IGF-I/-II mRNA expression and elevate SOCS1, SOCS3, and CISH transcript levels. However, TNFα was not effective in altering SOCS2 expression. In parallel experiment, LPS blockade of IGF-I/-II signals caused by GH could be partially reverted by TNFα receptor antagonism. At hepatocyte level, TNFα induction also triggered rapid phosphorylation of IκBα, MEK_1/2, ERK_1/2, MKK_3/6, P₃₈^MAPK, Akt, JAK₂, and STAT_1,3,5, and TNFα-induced SOCS1, SOCS3, and CISH mRNA expression could be negated by inhibiting the IKK/NFκB, MAPK, PI3K/Akt, and JAK/STAT cascades. Our findings, as a whole, suggest that local production of TNFα may interfere with IGF-I/-II induction by GH in the carp liver by up-regulation of SOCS1, SOCS3, and CISH via IKK/NFκB, MAPK, PI3K/Akt, and JAK/STAT-dependent mechanisms, which may contribute to GH resistance induced by endotoxin in carp species.

Surplus arginine reduced lipopolysaccharide induced transcription of proinflammatory genes in Atlantic salmon head kidney cells

In aquaculture production, studies of salmon health and interaction between pathogens and nutrition are of high importance. This study aimed to compare genes and pathways involved in salmon head kidney cells and liver cells, isolated from the same fish, towards polyinosinic acid: polycytidylic acid (poly I:C) and lipopolysaccharide (LPS), with and without addition of surplus arginine. Selected transcriptional responses of genes involved in inflammation, polyamine synthesis, oxidation and apoptosis were elucidated. For the genes related to inflammation, viperin, Mx and Toll like receptor 3 (TLR3), transcription were significantly upregulated by poly I:C in head kidney cells, while viperin was upregulated in liver cells. Surplus arginine did not affect poly I:C induced responses with the exception of reducing poly I:C induced Mx transcription in head kidney cells. Gene transcription of Interleukin 1β (IL-1β), Interleukin-8 (IL-8) and cyclooxygenase 2 (Cox2) were elevated during LPS treatment in all liver and head kidney cell cultures. In addition, LPS induced significantly, CD83 transcription in liver cells and TNF-α transcription in head kidney cells. Surplus arginine significantly reduced IL-8, Cox2 and TNF-α transcription in head kidney cells. LPS upregulated arginase in head kidney cells while poly I:C upregulated S-adenosyl methionine decarboxylase (SAMdc) transcription in liver cells. This suggests that LPS and poly I:C modulates genes involved in polyamine synthesis. In addition, in head kidney cells, surplus arginine, when cultured together with LPS, increased the transcription of ornithine decarboxylase (ODC) the limiting enzyme of polyamine synthesis. The genes involved with oxidation and apoptosis were not affect by any of the treatments in liver cells, while LPS decreased caspase 3 transcription in head kidney cells. In liver cells, protein expression of catalase was reduced by surplus arginine alone and when challenged with poly I:C. Both liver cells and head kidney cells isolated from the same individual fish responded to LPS and poly I:C, depending on the gene analyzed. Additionally, arginine could modulate transcription of pro-inflammatory genes induced by LPS in salmon immune cells, thus affecting salmon immunity.

Expression of immune-related genes of Nile tilapia Oreochromis niloticus after Gyrodactylus cichlidarum and Cichlidogyrus sclerosus infections demonstrating immunosupression in coinfection

Gyrodactylus cichlidarum and Cichlidogyrus sclerosus, two monogenean ectoparasite species commonly found on the body surface and gills of Nile tilapia (Oreochromis niloticus) respectively, inflicted considerable economic losses in intensive tilapia farming. In order to explore the immune response of tilapia against these two species of monogeneans, expression patterns of five immune-related genes were studied after singular G. cichlidarum or C. sclerosus infection and their coinfection. The transcription levels of IL-1β were up-regulated in the skin after G. cichlidarum infection, reaching a peak at day 5 PI, and in the gills after C. sclerosus infection (peaking at day 8 PI), with significant elevation only detected in the gills after high-dose C. sclerosus infection. A trend favoring increased gill TNF-α expression at day 8 PI of C. sclerosus infection was statistically significant only in the low-dose infection group. TNF-α expression in the skin did not change significantly after G. cichlidarum infection. TGF-β had extremely up-regulated expressions in the gills at day 8 PI after both high- and low-dose C. sclerosus infections, but its significantly promoted expression in the skin was observed only after infection of high-dose G. cichlidarum. Significantly increased expressions of HSP70 and COX-2 in the skin were detected after high-dose G. cichlidarum infections. In comparison to singular infection with either G. cichlidarum or C. sclerosus, concurrent infection resulted in significantly advanced expression of TGF-β in both skin and gills, and lower expressions at day 8 PI, and similar patterns were observed in the expression of IL-1β and TNF-α in the gills. G. cichlidarum infection on the body surface significantly down-regulated the expressions of TNF-α, TGF-β and COX-2 in the gills. In addition, the intensity of G. cichlidarum was significantly positively correlated with that of C. sclerosus (correlation index 0.922, p = 0.000) at day 2 PI under concurrent infection. These results contribute to the understanding of mucosal immunity of fish against monogenean infection, particularly when two monogenean species infect concurrently.

Comparison of polymeric immunoglobulin receptor between fish and mammals

Polymeric immunoglobulin receptor (pIgR) functions in transporting polymeric immunoglobulin across epithelial cells into external secretion in animals. During animal evolution, fish was situated at a transition point on the phylogenetic spectrum between species possessing only innate immunity (i.e., invertebrates) and species depending heavily on adaptive immunity (i.e., mammals). Previous studies reported that fish and mammals significantly differ in pIgR. This review summarized the differences in pIgR structure, function, and transcriptional regulation between fish and mammals. A model of the transcriptional regulation of the pIgR gene was suggested. In this model, microbes could activate Toll-like receptor, trigger the cascade reactions in the signaling pathway, and then activate transcription factors that regulate pIgR expression through combining with the pIgR promoter. This review provides some suggestions for further studies on the function and regulatory mechanism of pIgR in fish and other animals.

Novel Insights on the Regulation of B Cell Functionality by Members of the Tumor Necrosis Factor Superfamily in Jawed Fish

Most ligands and receptors from the tumor necrosis factor (TNF) superfamily play very important roles in the immune system. In particular, many of these molecules are essential in the regulation of B cell biology and B cell-mediated immune responses. Hence, in mammals, it is known that many TNF family members play a key role on B cell development, maturation, homeostasis, activation, and differentiation, also influencing the ability of B cells to present antigens or act as regulators of immune responses. Evolutionarily, jawed fish (including cartilaginous and bony fish) constitute the first animal group in which an adaptive immune response based on B cells and immunoglobulins is present. However, until recently, not much was known about the expression of TNF ligands and receptors in these species. The sequences of many members of the TNF superfamily have been recently identified in different species of jawed fish, thus allowing posterior analysis on the role that these ligands and receptors have on B cell functionality. In this review, we summarize the current knowledge on the impact that the TNF family members have in different aspects of B cell functionality in fish, also providing an in depth comparison with functional aspects of TNF members in mammals, that will permit a further understanding of how B cell functionality is regulated in these distant animal groups.

Characterization of Chicken Tumor Necrosis Factor-α, a Long Missed Cytokine in Birds

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine playing critical roles in host defense and acute and chronic inflammation. It has been described in fish, amphibians, and mammals but was considered to be absent in the avian genomes. Here, we report on the identification and functional characterization of the avian ortholog. The chicken TNF-α (chTNF-α) is encoded by a highly GC-rich gene, whose product shares with its mammalian counterpart 45% homology in the extracellular part displaying the characteristic TNF homology domain. Orthologs of chTNF-α were identified in the genomes of 12 additional avian species including Palaeognathae and Neognathae, and the synteny of the closely adjacent loci with mammalian TNF-α orthologs was demonstrated in the crow (Corvus cornix) genome. In addition to chTNF-α, we obtained full sequences for homologs of TNF-α receptors 1 and 2 (TNFR1, TNFR2). chTNF-α mRNA is strongly induced by lipopolysaccharide (LPS) stimulation of monocyte derived, splenic and bone marrow macrophages, and significantly upregulated in splenic tissue in response to i.v. LPS treatment. Activation of T-lymphocytes by TCR crosslinking induces chTNF-α expression in CD4⁺ but not in CD8⁺ cells. To gain insights into its biological activity, we generated recombinant chTNF-α in eukaryotic and prokaryotic expression systems. Both, the full-length cytokine and the extracellular domain rapidly induced an NFκB-luciferase reporter in stably transfected CEC-32 reporter cells. Collectively, these data provide strong evidence for the existence of a fully functional TNF-α/TNF-α receptor system in birds thus filling a gap in our understanding of the evolution of cytokine systems.

20 Years of fish immunotoxicology - what we know and where we are

Despite frequent field observations of impaired immune response and increased disease incidence in contaminant-exposed wildlife populations, immunotoxic effects are rarely considered in ecotoxicological risk assessment. The aim of this study was to review the literature on immunotoxic effects of chemicals in fish to quantitatively evaluate (i) which experimental approaches were used to assess immunotoxic effects, (ii) whether immune markers exist to screen for potential immunotoxic activities of chemicals, and (iii) how predictive those parameters are for adverse alterations of fish immunocompetence and disease resistance. A total of 241 publications on fish immunotoxicity were quantitatively analyzed. The main conclusions included: (i) To date, fish immunotoxicology focused mainly on innate immune responses and immunosuppressive effects. (ii) In numerous studies, the experimental conditions are poorly documented, as for instance age or sex of the fish or the rationale for the selected exposure conditions is often missing. (iii) Although a broad variety of parameters were used to assess immunotoxicity, the rationale for the choice of measured parameters was often not given, remaining unclear how they link to the suspected immunotoxic mode of action of the chemicals. (iv) At the current state of knowledge, it is impossible to identify a set of immune parameters that could reliably screen for immunotoxic potentials of chemicals. (v) Similarly, in fish immunotoxicology there is insufficient understanding of how and when chemical-induced modulations of molecular/cellular immune changes relate to adverse alterations of fish immunocompetence, although this would be crucial to include immunotoxicity in ecotoxicological risk assessment.

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.

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.

Dactylogyrus intermedius parasitism enhances Flavobacterium columnare invasion and alters immune-related gene expression in Carassius auratus

The monogenean Dactylogyrus intermedius and the bacterium Flavobacterium columnare are 2 common pathogens in aquaculture. The objective of the present study was to examine the effect of prior parasitism by D. intermedius on the susceptibility of goldfish to F. columnare and to explore the potential immune mechanisms related to the parasite infection. A F. columnare challenge trial was conducted between D. intermedius-parasitized and non-parasitized goldfish. The F. columnare load in gill, kidney, spleen and liver were compared. The expression of immune-related genes (IL-1β2, TNF-α1, TGF-β, iNOS-a, C3 and Lyz) in gill and kidney of D. intermedius-only infected and uninfected control fish were evaluated. D. intermedius-parasitized goldfish exhibited higher mortality and significantly higher loads (3051 to 537,379 genome equivalents [GEs] mg(-1)) of F. columnare, which were 1.13 to 50.82-fold higher than non-parasitized fish (389 to 17,829 GEs mg(-1)). Furthermore, the immune genes IL-1β2, TNF-α1, iNOS-a and Lyz were up-regulated while the TGF-β and C3 were down-regulated in the gill and kidney of parasite-infected fish compared to the non-parasitized controls. The down-regulation TGF-β and C3 was especially noteworthy, as this might indicate the suppression of the host immune functions due to the parasitism by D. intermedius. Taken together, these data demonstrate that parasite infection can enhance bacterial invasion and presents a hypothesis, based on gene expression data, that modulation of host immune response could play a role.

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.

Expression analysis of the Atlantic bluefin tuna (Thunnus thynnus) pro-inflammatory cytokines, IL-1β, TNFα1 and TNFα2 in response to parasites Pseudocycnus appendiculatus (Copepoda) and Didymosulcus katsuwonicola (Digenea)

Pro-inflammatory cytokines play an important role in teleost defence against numerous types of pathogens, therefore are often used as biomarkers during various infections. In order to evaluate Atlantic bluefin tuna IL-1β, TNFα1 and TNFα2 induction by PAMPs, we quantified their expression during in vitro stimulation of peripheral blood leukocytes by LPS and Poly I:C. Furthermore, their role in acute and chronic parasitic infection was examined during natural infection of Pseudocycnus appendiculatus (Copepoda) and Didymosulcus katsuwonicola (Digenea), as well as during leukocyte exposure to total protein extracts isolated from two parasite species. Induction of ABT IL-1β and TNFα2 by PAMPs and protein extracts from D. katsuwonicola and P. appendiculatus, as well as during natural infection with two parasites, suggests these cytokines play an important role in inflammation, being engaged in controlling parasite infections, in contrast to ABT TNFα1. Cellular innate response to the digenean D. katsuwonicola showed rather chronic character, resulting with parasite encapsulation in connective tissue. Mast cells, eosinophils, goblet cells, and occasional rodlet cells found at the site of infection, along with the induction of TNFα2, suggest the presence of a moderate inflammatory reaction that fails to seriously endanger digenean existence. In contrast, copepod P. appendiculatus, attached to the gill epithelium by clamping, caused direct tissue disruption with undergoing necrotic or apoptotic processes, and extensive proliferation of rodlet and goblet cells. Differential expression patterns of target cytokines in tissue surrounding two parasites and in vitro PBL model suggest that quality and quantity of tuna immune response is conditioned by parasite adaptive mechanisms and pathogenicity.

Effect of dietary glutamine on growth performance, non-specific immunity, expression of cytokine genes, phosphorylation of target of rapamycin (TOR), and anti-oxidative system in spleen and head kidney of Jian carp (Cyprinus carpio var. Jian)

This study was designed to investigate the effects of dietary glutamine on the growth performance, cytokines, target of rapamycin (TOR), and antioxidant-related parameters in the spleen and head kidney of juvenile Jian carp (Cyprinus carpio var. Jian). Fish were fed the basal (control) and glutamine-supplemented (12.0 g glutamine kg(-1) diet) diets for 6 weeks. Results indicated that the dietary glutamine supplementation improved the growth performance, spleen protein content, serum complement 3 content, and lysozyme activity in fish. In the spleen, glutamine down-regulated the expression of the interleukin 1 and interleukin 10 genes, and increased the level of phosphorylation of TOR protein. In the head kidney, glutamine down-regulated the tumor necrosis factor α and interleukin 10 gene expressions, phosphorylated and total TOR protein levels, while up-regulated the transforming growth factor β2 gene expression. Furthermore, the protein carbonyl content was decreased in the spleen of fish fed glutamine-supplemented diet; conversely, the anti-hydroxyl radical capacity and glutathione content in the spleen were increased by glutamine. However, diet supplemented with glutamine did not affect the lipid peroxidation, anti-superoxide anion capacity, and antioxidant enzyme activities in the spleen. Moreover, all of these antioxidant parameters in the head kidney were not affected by glutamine. Results from the present experiment showed the importance of dietary supplementation of glutamine in benefaction of the growth performance and several components of the innate immune system, and the deferential role in cytokine gene expression, TOR kinase activity, and antioxidant status between the spleen and head kidney of juvenile Jian carp.

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.

Host specificity, pathogenicity, and mixed infections of trypanoplasms from freshwater fishes

This work summarizes the results of the 8-year study focused on Trypanoplasma sp. parasitizing freshwater fishes in the vicinity of Kyiv, Ukraine. Out of 570 fish specimens of 2 different species analyzed, 440 individuals were found to be infected. The prevalence of infection ranged from 24 % in Abramis brama Linnaeus (freshwater bream) to 100 % in Cobitis taenia Linnaeus (spined loach). The level of parasitemia also varied between moderate in freshwater bream and very high in spined loach. Interestingly, no clinical manifestations of trypanoplasmosis were observed even in extremely heavily infected C. taenia. We hypothesize that different species may differ in evolutionary timing allowing for reciprocal adaptation of the members of the "host-parasite" system. Molecular analysis of the 18S rRNA sequences revealed that several specimens were simultaneously infected with at least two different trypanoplasm species. To the best of our knowledge, this is the first report of the mixed infection with fish trypanoplasms.

Pro- and anti-inflammatory cytokine expression in immune organs of the common carp exposed to atrazine and chlorpyrifos

Atrazine (ATR) and chlorpyrifos (CPF) are toxic and subject to long-term in vivo accumulation in different aquatic species throughout the world. The purpose of the present study was to examine the effect of ATR, CPF and combined ATR/CPF exposure on cytokines in the head kidney and spleen of common carp (Cyprinus carpio L.). The carp were sampled after a 40-d exposure to CPF and ATR, individually or in combination, followed by a 40-d recovery to measure the mRNA expression of IL-6fam (IL-6), IL-8, TNF-α, IL-10 and TGF-β1 (TGF-β) in the head kidney and spleen tissues. These results showed that the expression of cytokines IL-6, IL-8 and TNF-α in the head kidney and spleen was upregulated following ATR, CPF and mixed ATR/CPF exposure compared with the control group. The expression of IL-10 and TGF-β mRNA was significantly inhibited in both head kidney and spleen of carp exposed to ATR, CPF and the ATR/CPF mixture. The results suggested that long-term exposure of ATR, CPF and the ATR/CPF mixture in aquatic environments can induce the dysregulation of pro-/anti-inflammatory cytokine expression. The information regarding the effects of ATR and CPF on cytokine mRNA expression generated in this study will be important information for pesticides toxicology evaluation.

Effects of dietary β-1,3/1,6-glucan on the antioxidant and digestive enzyme activities of Pacific red snapper (Lutjanus peru) after exposure to lipopolysaccharides

The effect of β-1,3/1,6-glucan, derived from yeast, on growth, antioxidant, and digestive enzyme performance of Pacific red snapper Lutjanus peru before and after exposure to lipopolysaccharides (LPS) was investigated. The β-1,3/1,6-glucan was added to the basal diet at two concentrations (0.1 and 0.2 %). The treatment lasted 6 weeks, with sampling at regular intervals (0, 2, 4, and 6 weeks). At the end of this period, the remaining fish from either control or β-glucan-fed fish were injected intraperitoneally with LPS (3 mg kg(-1)) or with sterile physiological saline solution (SS) and then sampled at 0, 24, and 72 h. The results showed a significant increase (P < 0.05) in growth performance after 6 weeks of feeding with β-glucan. Superoxide dismutase (SOD) activity in liver was significantly higher in diets containing 0.1 % β-glucan in weeks 4 and 6, compared to the control group. β-Glucan supplementation at 0.1 and 0.2 % significantly increased aminopeptidase, trypsin, and chymotrypsin activity. At 72 h after injection of LPS, we observed a significant increase in catalase activity in liver from fish fed diets supplemented with 0.1 and 0.2 % β-glucan; SOD activity increased in fish fed with 0.1 % β-glucan in relation to those injected with SS. Feed supplemented with β-1,3/1,6-glucan increased growth, antioxidant activity, and digestive enzyme activity in Pacific red snapper.

Immunity against selected piscine flagellates

This discussion is on immune response to Amyloodinium ocellatum, Cryptobia salmositica, Trypanoplasma borreli and Trypanosoma carassii. Piscidin and histone-like proteins enhance innate resistance to Amyloodinium. Fish that are naturally resistant to Cryptobia and Trypanoplasma can be bred. Cryptobia resistance in charr is controlled by a dominant Mendelian locus and protection is via the Alternative Pathway of Complement Activation. Studies on Cryptobia-tolerant charr may lead to production of transgenic Cryptobia-tolerant salmon. Innate response to T. borreli is associated with NO in macrophages. Transferrin regulates resistance and carp have been bred for transferrin genotypes. Recovered fish are protected from homologous challenge, and complement fixing antibodies are crucial in protection. Studies on antigens in T. carassii may lead to a vaccine. There are two vaccines against cryptobiosis; a single dose of the attenuated vaccine protects salmonids. On challenge fish inoculated with the metalloprotease-DNA vaccine do not have the disease and they recover faster.

A short history of research on immunity to infectious diseases in fish

This review describes the history of research on immunity to infectious diseases of fish in the period between 1965 and today. Special attention is paid to those studies, which are dealing with the interaction between immune system and invading pathogens in bony fish. Moreover, additional biographic information will be provided of people involved. In the 1960s and 1970s the focus of most studies was on humoral (Ig, B-cell) responses. Thorough studies on specific cellular (T-cell) responses and innate immunity (lectins, lysozyme, interferon, phagocytic cells) became available later. In the period between 1980 and today an overwhelming amount of data on regulation (e.g. cell cooperation, cytokines) and cell surface receptors (e.g. T-cell receptor; MHC) was published. It became also clear, that innate responses were often interacting with the acquired immune responses. Fish turned out to be vertebrates like all others with a sophisticated immune system showing specificity and memory. These basic data on the immune system could be applied in vaccination or in selection of disease resistant fish. Successful vaccines against bacterial diseases became available in the 1970s and 1980s. Effective anti-viral vaccines appeared from the 1980s onwards. There is no doubt, that Fish Immunology has become a flourishing science by the end of the 20th century and has contributed to our understanding of fish diseases as well as the success of aquaculture.

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.

The cytokine networks of adaptive immunity in fish

Cytokines, produced at the site of entry of a pathogen, drive inflammatory signals that regulate the capacity of resident and newly arrived phagocytes to destroy the invading pathogen. They also regulate antigen presenting cells (APCs), and their migration to lymph nodes to initiate the adaptive immune response. When naive CD4+ T cells recognize a foreign antigen-derived peptide presented in the context of major histocompatibility complex class II on APCs, they undergo massive proliferation and differentiation into at least four different T-helper (Th) cell subsets (Th1, Th2, Th17, and induced T-regulatory (iTreg) cells in mammals. Each cell subset expresses a unique set of signature cytokines. The profile and magnitude of cytokines produced in response to invasion of a foreign organism or to other danger signals by activated CD4+ T cells themselves, and/or other cell types during the course of differentiation, define to a large extent whether subsequent immune responses will have beneficial or detrimental effects to the host. The major players of the cytokine network of adaptive immunity in fish are described in this review with a focus on the salmonid cytokine network. We highlight the molecular, and increasing cellular, evidence for the existence of T-helper cells in fish. Whether these cells will match exactly to the mammalian paradigm remains to be seen, but the early evidence suggests that there will be many similarities to known subsets. Alternative or additional Th populations may also exist in fish, perhaps influenced by the types of pathogen encountered by a particular species and/or fish group. These Th cells are crucial for eliciting disease resistance post-vaccination, and hopefully will help resolve some of the difficulties in producing efficacious vaccines to certain fish diseases.

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.

Fish cell cultures as in vitro models of inflammatory responses elicited by immunostimulants. Expression of regulatory genes of the innate immune response

We report the differential expression of various genes related to the regulation of the innate immune responses, including pro-inflammatory (IL-1β1, IL-8, TNF-α1, TNF-α2) and immune-suppressing (IL-10) cytokines, interferon-induced Mx-1 protein, enzymes regulating nitric oxide (inducible nitric oxide synthase, arginase-2) and eicosanoid (COX-2) production, and Toll-like pathogen pattern-recognition receptors TLR-3, TLR-5 and TLR-9, in two lympho-haematopoietic stromal cell lines derived from the spleen (trout splenic stroma, TSS) and the pronephros (trout pronephric stroma-2, TPS-2) of rainbow trout (Oncorhynchus mykiss), as well as in primary cultures of rainbow trout head kidney macrophages, after their exposure to the well-known immunostimulants LPS, levamisole and poly I:C. Although there were differences in the responses between the two stromal cell lines, using reverse transcription followed by real time polymerase chain reaction (RT-qPCR) we demonstrated that exposure to the immunostimulants, particularly poly I:C and LPS, resulted in significant changes in the expression of the immunoregulatory genes in the two stromal cell lines in many cases their responses resembling in fold change magnitudes and in response profiles to those observed in the primary macrophage cultures. Exposure to poly I:C and, with lower fold change values, to LPS produced upregulation of the pro- (IL-1β, IL-8, TNF-α) and anti-inflammatory (IL-10) cytokine genes, as well as of the Mx-1 gene. Furthermore, the immunostimulation elicited the upregulation of COX-2, iNOS and arginase-2 genes in the cell lines. Likewise, the TSS and TPS-2 cell lines significantly upregulated the expression of TLR-3, TLR-5 and TLR-9 genes after exposure to the immunostimulants, thus explaining the ability of the stromal cells to recognise and respond to the immunostimulants. Such results give support to an important role of lympho-haematopoietic stromal cells in the development and control of pro-inflammatory responses in fish. The upregulation of genes of pro-inflammatory cytokines and of mediators of the innate immune responses correlates well with the previously demonstrated functional capacities, including phagocytosis, microbicidal activity and NO production, exhibited by the TSS and TPS-2 stromal cell lines when exposed to the same immunostimulants. On the other hand, the expression of immunosuppressing genes (IL-10, COX-2 and arginase-2) demonstrate that the lympho-haematopoietic stromal cells are also able to contribute to the control of inflammatory responses. This study reinforce the possibility of using histotypic cell cultures, as those formed by the TSS and TPS-2 cell lines, formed by heterogeneous cell populations that partially replicates the cell-cell and cell-extracellular matrix interactions, to develop cost-effective and repetitive in vitro systems for the screening of immunostimulant candidates for aquaculture, as they are able to replicate in vitro immune regulatory networks occurring in vivo.

Oxidative burst and nitric oxide responses in carp macrophages induced by zymosan, MacroGard(®) and selective dectin-1 agonists suggest recognition by multiple pattern recognition receptors

β-Glucans are glucose polymers that are found in the cell walls of plants, bacteria, certain fungi, mushrooms and the cell wall of baker's yeast. In mammals, myeloid cells express several receptors capable of recognizing β-glucans, with the C-type lectin receptor dectin-1 in conjunction with Toll-like receptor 2 (TLR2), considered key receptors for recognition of β-glucan. In our studies to determine the possible involvement of these receptors on carp macrophages a range of sources of β-glucans were utilized including particulate β-glucan preparations of baker's yeast such as zymosan, which is composed of insoluble β-glucan and mannan, and MacroGard(®), a β-glucan-based feed ingredient for farmed animals including several fish species. Both preparations were confirmed TLR2 ligands by measuring activation of HEK293 cells transfected with human TLR2 and CD14, co-transfected with a secreted embryonic alkaline phosphatase (SEAP) reporter gene. In addition, dectin-1-specific ligands in mammals i.e. zymosan treated to deplete the TLR-stimulating properties and curdlan, were monitored for their effects on carp macrophages by measuring reactive oxygen and nitrogen radicals production, as well as cytokine gene expression by real-time PCR. Results clearly show the ability of carp macrophages to strongly react to particulate β-glucans with an increase in the production of reactive oxygen and nitrogen radicals and an increase in cytokine gene expression, in particular il-1β, il-6 and il-11. We identified carp il-6, that was previously unknown. In addition, carp macrophages are less, but not unresponsive to selective dectin-1 agonists, suggesting recognition of β-glucans by multiple pattern recognition receptors that could include TLR but also non-TLR receptors. Candidate receptors for recognition of β-glucans are discussed.

First evidence of the possible implication of the 11-deoxycorticosterone (DOC) in immune activity of Eurasian perch (Perca fluviatilis, L.): comparison with cortisol

Cortisol, the main corticosteroid in fish, is frequently described as a modulator of fish immune system. Moreover, 11-deoxycorticosterone (DOC) was shown to bind and transcriptionally activate the mineralocorticoid receptor and may act as a mineralocorticoid in fish. Immune modulations induced by intraperitoneal injections of these two corticosteroids were assessed in Eurasian perch juveniles. Cortisol and DOC were injected at 0.8 mg kg(-1) and 0.08 mg kg(-1) body weight respectively. Cortisol increased plasma lysozyme activity 72 h post-injection, C-type lysozyme expression in spleen from 1 to 72 h post-injection, and favoured blood neutrophils at the expense of a mixture of lymphocytes and thrombocytes. Moreover, 6 h after injection, cortisol reduced expression levels of the pro-inflammatory cytokine TNF-α in spleen. DOC had no effects on the immune variables measured in plasma, but increased expression levels of C-type lysozyme and apolipoprotein A1 mRNA in both gills and spleen. Meanwhile, DOC stimulated its putative signalling pathway by increasing expression of mineralocorticoid receptor and 11β-hydroxysteroid dehydrogenase-2 in spleen. These results confirmed the role of cortisol as an innate, short term immune stimulator. For the first time, DOC is described as a possible immune stimulator in fish.

Expression of immune-related genes in goldfish gills induced by Dactylogyrus intermedius infections

Dactylogyrus intermedius, an oviparous monogenean parasite, is regarded as a devastating pathogen in freshwater aquaculture and ornamental fish trade, and accounts for significant economic losses worldwide. The study was undertaken to determine the differential expression of immune-related genes TNFα1, TNFα2, IL-1β2, TGFβ, iNOSa and iNOSb in goldfish gills during D. intermedius infection by real-time quantitative PCR. The results show that the expression of the pro-inflammatory cytokines (IL-1β2, TNFα1 and TNFα2) and the anti-inflammatory cytokine (TGFβ) were up-regulated at day 7 p.i. (post infection). The mRNA levels of these cytokines returned to normal levels or were down-regulated at day 21 p.i. In the cases of iNOSa and iNOSb, a significant up-regulation in iNOSa transcription levels were seen at day 14 p.i. while the expression of iNOSb gene showed a distinct up-regulation at day 7 p.i. Additionally, this study was conducted to investigate the expression of immune-related genes in different degrees of goldfish experimentally infected with the monogenean D. intermedius. The results indicated that D. intermedius infection might regulate the fish immunity by showing differential expression levels of immune-related gene. The study confirms goldfish gill acts as an important source of inflammatory molecules, as well as an active modulator of local inflammation after initially infected with D. intermedius. Moreover, the results obtained in this study could be useful towards understanding the susceptibility of goldfish to D. intermedius and mechanisms involved in protection of goldfish to ectoparasitic infections.

Advances in research of fish immune-relevant genes: a comparative overview of innate and adaptive immunity in teleosts

Fish is considered to be an important model in comparative immunology studies because it is a representative population of lower vertebrates serving as an essential link to early vertebrate evolution. Fish immune-relevant genes have received considerable attention due to its role in improving understanding of both fish immunology and the evolution of immune systems. In this review, we discuss the current understanding of teleost immune-relevant genes for both innate and adaptive immunity, including pattern recognition receptors, antimicrobial peptides, complement molecules, lectins, interferons and signaling factors, inflammatory cytokines, chemokines, adaptive immunity relevant cytokines and negative regulators, major histocompatibility complexes, immunoglobulins, and costimulatory molecules. The implications of these factors on the evolutionary history of immune systems were discussed and a perspective outline of innate and adaptive immunity of teleost fish was described. This review may provide clues on the evolution of the essential defense system in vertebrates.

The innate immune-related genes in catfish

Catfish is one of the most important aquaculture species in America (as well as in Asia and Africa). In recent years, the production of catfish has suffered massive financial losses due to pathogen spread and breakouts. Innate immunity plays a crucial role in increasing resistance to pathogenic organisms and has generated increasing interest in the past few years. This review summarizes the current understanding of innate immune-related genes in catfish, including pattern recognition receptors, antimicrobial peptides, complements, lectins, cytokines, transferrin and gene expression profiling using microarrays and next generation sequencing technologies. This review will benefit the understanding of innate immune system in catfish and further efforts in studying the innate immune-related genes in fish.

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

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

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 role of neuromedin U during inflammatory response in the common carp

In the current study, we cloned and characterized the neuromedin U (NMU) gene from the common carp Cyprinus carpio L., and identified its participation in immune responses in the teleost. Five isoforms of the preproNMU genes were generated by alternative splicing and isolated from carp. The longest form of the carp preproNMU1 (isoform 1) cDNA was composed of 803 bp, and contained an 18 bp 5'-UTR, a 212 bp 3'-UTR and a 573 bp open reading frame, which translates into a peptide comprising 190 amino acid (aa) residues. The remaining carp preproNMU isoforms were composed of 175 (preproNMU2), 158 (preproNMU3), 150 (preproNMU4) and 133 (preproNMU5) aa residues. Isoforms 1-3 contained four processing signals (KR or RR), while isoforms 4 and 5 contained only two processing signals. High homology was demonstrated among fish and other vertebral NMU at the biologically active C-terminal region (aa position 175-182). Carp preproNMU transcript variants were identified in various tissues, and the expression pattern has been shown to change depending on feeding status. Moreover, it was shown that the expression of preproNMU3 and preproNMU5 was increased following treatment with bacterial or viral mimics. Finally, we investigated the functional aspect of carp NMU using a synthetic NMU peptide. The peptide was found to increase the expression of inflammation-related cytokine genes in intestinal cells within 1 h of treatment. In addition, the activation of phagocytic cells was also stimulated by the NMU peptide. The discovery of NMU in carp allows for a further understanding of immune regulation by biologically active substances.

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.

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.

Immunotoxic effects of environmental toxicants in fish - how to assess them?

Numerous environmental chemicals, both long-known toxicants such as persistent organic pollutants as well as emerging contaminants such as pharmaceuticals, are known to modulate immune parameters of wildlife species, what can have adverse consequences for the fitness of individuals including their capability to resist pathogen infections. Despite frequent field observations of impaired immunocompetence and increased disease incidence in contaminant-exposed wildlife populations, the potential relevance of immunotoxic effects for the ecological impact of chemicals is rarely considered in ecotoxicological risk assessment. A limiting factor in the assessment of immunotoxic effects might be the complexity of the immune system what makes it difficult (1) to select appropriate exposure and effect parameters out of the many immune parameters which could be measured, and (2) to evaluate the significance of the selected parameters for the overall fitness and immunocompetence of the organism. Here, we present - on the example of teleost fishes - a brief discussion of how to assess chemical impact on the immune system using parameters at different levels of complexity and integration: immune mediators, humoral immune effectors, cellular immune defenses, macroscopical and microscopical responses of lymphoid tissues and organs, and host resistance to pathogens. Importantly, adverse effects of chemicals on immunocompetence may be detectable only after immune system activation, e.g., after pathogen challenge, but not in the resting immune system of non-infected fish. Current limitations to further development and implementation of immunotoxicity assays and parameters in ecotoxicological risk assessment are not primarily due to technological constraints, but are related from insufficient knowledge of (1) possible modes of action in the immune system, (2) the importance of intra- and inter-species immune system variability for the response against chemical stressors, and (3) deficits in conceptual and mechanistic assessment of combination effects of chemicals and pathogens.

Neuroendocrine-immune interaction in fish: differential regulation of phagocyte activity by neuroendocrine factors

Coping with physical, chemical and biological disturbances depends on an extensive repertoire of physiological, endocrinological and immunological responses. Fish provide intriguing models to study bi-directional interaction between the neuroendocrine and the immune systems. Macrophages and granulocytes are the main actors in the first and rapid innate immune response. They are resident in different organs and are moreover rapidly recruited and activated upon infection. They act in response to recognition of pathogen-associated molecular patterns (PAMPs) via a repertoire of surface and intracellular receptors by inducing a plethora of defense reactions aiming to eradicate the pathogen. Subsequent production of inflammatory mediators stimulates other leukocytes required to develop an adaptive and specific antibody response. The type of phagocyte reaction will therefore depend on their differentiation state, specific receptor repertoire and their specific location. Apart from these pathogen induced responses, immune reactivity may be modulated by neuroendocrine factors. Over the last years we extensively studied changes in carp stress axis activity and the effect of its end-products on the immune system in an acute stress paradigm. We focus on specific neuroendocrine receptors on leukocytes and their effect on crucial phagocyte activities. We performed identification and functional analyses of different glucocorticoid, opioid and adrenergic receptors on carp phagocytes. Results show that their ligands of neuroendocrine origin may have substantial impact on specific phagocyte functions in a differential way. Inflammatory and microbicidal responses fight pathogens but may be detrimental to the host tissue. Neuroendocrine modulation may regulate inflammation to reach an optimum defense while preventing excessive host cell damage.

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

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