Mx expression in Atlantic salmon (Salmo salar L.) parr in response to Listonella anguillarum bacterin, lipopolysaccharide and chromosomal DNA

Insights into Early Ontogenesis of Salmo salar: RNA Extraction, Housekeeping Gene Validation and Transcriptional Expression of Important Primordial Germ Cell and Sex-Determination Genes

The challenge in extracting high-quality RNA impedes the investigation of the transcriptome of developing salmonid embryos. Furthermore, the mRNA expression pattern of important PGC and SD genes during the initial embryonic development of Salmo salar is yet to be studied. So, in the present study, we aimed to isolate high-quality RNA from eggs and developing embryos to check vasa, dnd1, nanos3a, sdf1, gsdf, amh, cyp19a, dmrt1 and foxl2 expression by qPCR. Additionally, four HKGs (GAPDH, UB2L3, eEf1a and β-actin) were validated to select the best internal control for qPCR. High-quality RNA was extracted, which was confirmed by spectrophotometer, agarose gel electrophoresis and Agilent TapeStation analysis. UB2L3 was chosen as a reference gene because it exhibited lower intra- and inter-sample variation. vasa transcripts were expressed in all the developmental stages, while dnd1 was expressed only up to 40 d°C. Nanos3a was expressed in later stages and remained at its peak for a shorter period, while sdf1 showed an irregular pattern of mRNA expression. The mRNA expression levels of SD genes were observed to be upregulated during the later stages of development, prior to hatching. This study presents a straightforward methodology for isolating high-quality RNA from salmon eggs, and the resulting transcript profiles of significant PGC and SD genes in S. salar could aid in improving our comprehension of reproductive development in this commercially important species.

A myxovirus resistance like protein involved in CgIFNLP mediated immune response of oyster Crassostrea gigas

The myxovirus resistance (Mx) proteins belong to interferon (IFN)-induced dynamin GTPase and play a pivotal role in the inhibition of replication of numerous viruses. In the present study, an Mx homologue (designated as CgMx1) was identified from oyster Crassostrea gigas. The open reading frame (ORF) of CgMx1 cDNA was of 1689 bp encoding a peptide of 562 amino acid residues. There was an N-terminal dynamin GTPase domain in the predicted peptide, which consisted of a tripartite GTP-binding motif (GDXXSGKS, DLPG and T/NKXD). The deduced amino acid sequence of CgMx1 shared 30-39% similarity with other Mx family members. And CgMx1 was clustered with Mx from H. discus, and then assigned into the invertebrate branch of the phylogenetic tree. The mRNA transcripts of CgMx1 were constitutively distributed in all the tested tissues, with the highest level in haemocytes (1342.45-fold of labial palps, p < 0.05). The mRNA expression of CgMx1 in haemocytes was significantly up-regulated to the highest level at 6 h (13.14-fold, p < 0.001) after poly (I:C) treatment and at 24 h (66.28-fold, p < 0.001) after recombinant IFN-like protein (rCgIFNLP) stimulation, respectively. CgMx1 protein was found to distribute in both the cytoplasm and nucleus of haemocytes. In the oysters with CgIFNLP and signal transducer and activator of transcription (CgSTAT) silenced by RNAi, the mRNA expression of CgMx1 decreased significantly in the haemocytes at 12 h after poly (I:C) stimulation, which was 0.02-fold and 0.04-fold of that in EGFP-RNAi oysters (p < 0.001), respectively. Meanwhile, EMSA assay revealed that CgSTAT was able to transactivate CgMx1 promoter through directly binding to its interferon-stimulated response element (ISRE) and gamma interferon activation site (GAS). The above results indicated that CgMx1 participated in the immune response of C. gigas through the signal pathway mediated by CgIFNLP and CgSTAT.

Screening of New Potential Probiotics Strains against Photobacterium damselae Subsp. piscicida for Marine Aquaculture

On intensive fish farms, 10% of the population dies exclusively from pathogens, and Photobacterium damselae subsp. Piscicida (Ph. damselae subsp. Piscicida), the bacteria causing pasteurellosis in marine aquaculture, is one of the major pathogens involved. The objective of this study was to obtain new probiotic strains against pasteurellosis in order to limit the use of chemotherapy, avoiding the environmental repercussions generated by the abusive use of these products. In this study, 122 strains were isolated from the gills and intestines of different marine fish species and were later evaluated in vitro to demonstrate the production of antagonistic effects, the production of antibacterial substances, adhesion and growth to mucus, resistance to bile and resistance to pH gradients, as well as its harmlessness and the dynamic of expression of immune-related genes by real-time PCR after administration of the potential probiotic in the fish diet. Only 1/122 strains showed excellent results to be considered as a potential probiotic strain and continue its characterization against Ph. damselae subsp. piscicida to determine its protective effect and elucidating in future studies its use as a possible probiotic strain for marine aquaculture.

Labeo rohita Mx1 exhibits the critical structural motifs of the family of large GTPases of mammals and is activated by rhabdovirus vaccination and bacterial RNA stimulations

Myxovirus resistance (Mx) proteins belonging to the dynamin superfamily of high molecular weight GTPases exist in various isoforms and play crucial role in innate immunity. In addition to the isoforms, Mx1 also plays important role in exerting its anti-viral actions against a broad range of animal RNA viruses. In rohu (Labeo rohita), mx1 full-length cDNA sequence consists of 2440 nucleotides (nt) encoding 628 amino acids (aa) polypeptide of 71.289 kDa. Structurally, it belongs to the family of large GTPases with one DYNc domain (13-257aa) comprising of dynamin family motifs (LPRGSGIVTR) and the tripartite GTP-binding motifs (GDQSSGKS, DLPG and TKPD) at the N-terminal and one GED domain (537-628aa) at C-terminus. Rohu Mx1 is closely related to zebrafish Mx1 and is widely expressed in gill, liver, kidney, spleen and blood. In response to rhabdovirus vaccinations, poly I:C stimulation and bacterial infections, mx1 gene expression in rohu was significantly (p < 0.05) induced in majority of the tested organs/tissues. Stimulation of rohu gill cell line with bacterial RNA also induced mx1 gene expression. Together these data suggest the important role of Mx1 in innate immunity in rohu against wide spectrum of fish pathogens.

Myxovirus resistance (Mx) gene and its differential expression regulated by three type I and two type II IFNs in mandarin fish, Siniperca chuatsi

Interferons (IFNs) can induce the expression of IFN-stimulated genes (ISGs), such as myxovirus resistance (Mx) protein, to inhibit virus replication. In this study, the expression of Mx gene in mandarin fish, and the IFN-sensitive response elements (ISREs) and gamma-interferon activated sites (GASs) in the promoter of Mx gene were analyzed in relation to the stimulation of three distinct type I IFNs, IFNc, IFNd and IFNh, and two type II IFNs, IFN-γ and IFN-γ related molecule (IFN-γrel). A single Mx gene was found in mandarin fish, and its expression was highly and constitutively observed in all organs/tissues examined. The Mx gene was significantly induced in vivo for 120 h following infectious spleen and kidney necrosis virus (ISKNV) infection. Furthermore, the overexpression and recombinant of IFNh, IFNc, as well as IFN-γ can significantly induce Mx expression in MFF-1 cells at transcript and protein levels, although all the three type I IFNs and the two type II IFNs can activate the Mx promoter. In addition, ISRE1 which is the proximal one among the three predicted ISREs seems to be the important ISRE for the higher and efficient activation of the Mx promoter. However, the possible interaction between the GASs and type II IFN signalling molecules require further study.

Protective immunity against rock bream iridovirus (RBIV) infection and TLR3-mediated type I interferon signaling pathway in rock bream (Oplegnathus fasciatus) following poly (I:C) administration

In this study, we evaluated the potential of poly (I:C) to induce antiviral status for protecting rock bream from RBIV infection. Rock bream injected with poly (I:C) at 2 days before infection (1.1 × 10⁴) at 20 °C had significantly higher protection with RPS 13.4% and 33.4% at 100 and 200 μg/fish, respectively, through 100 days post infection (dpi). The addition of boost immunization with poly (I:C) at before/post infection at 20 °C clearly enhanced the level of protection showing 33.4% and 60.0% at 100 and 200 μg/fish, respectively. To investigate the development of a protective immune response, rock bream were re-infected with RBIV (1.1 × 10⁷) at 200 dpi. While 100% of the previously unexposed fish died, 100% of the previously infected fish survived. Poly (I:C) induced TLR3 and Mx responses were observed at several sampling time points in the spleen, kidney and blood. Moreover, significantly high expression levels of IRF3 (2.9- and 3.1-fold at 1 d and 2 days post administration (dpa), respectively), ISG15 and PKR expression (5.4- and 10.2-fold at 2 dpa, respectively) were observed in the blood, but the expression levels were low in the spleen and kidney after poly (I:C) administration. Our results showed the induction of antiviral immune responses and indicate the possibility of developing long term preventive measures against RBIV using poly (I:C).

Autochthonous Bacterial Isolates Successfully Stimulate In vitro Peripheral Blood Leukocytes of the European Sea Bass (Dicentrarchus labrax)

Commercially available probiotics are routinely administered as feed supplements in aquaculture important species. Among them, the European sea bass (Dicentrarchus labrax) is the most widely reared fish in the Mediterranean, whose rearing systems are highly variable between countries, affecting at some level the sustainability of production. After random isolation of autochthonous gut bacteria of the sea bass, their identification and pathogenicity testing, we have selected three potentially probiotic isolates; Pseudoalteromonas sp., Alteromonas sp., and Enterovibrio coralii. Selected isolates were tested and their immunostimulative efficiency was compared with a commercially available Lactobacillus casei isolate, inferring inflammatory, apoptotic and anti-pathogen response of sea bass’ peripheral blood leukocytes. Phagocytic activity, respiratory burst, and expression of lysozyme, Mx protein, caspase 3, TNF-α, IL-10 genes was measured 1, 3, 5, and 12 h post-stimulation by four bacterial isolates to evaluate early kinetics of the responses. Best immunostimulative properties were observed in Pseudoalteromonas-stimulated leukocytes, followed by Alteromonas sp. and L. casei, while Enterovibrio coralii failed to induce significant stimulation. Based on such in vitro assay intestinal autochthonous bacterial isolates showed to have better immunostimulative effect in sea bass compared to aquaculture-widely used L. casei, and further steps need to engage tank and field feeding trials to evaluate long-term prophylactic suitability of the chosen isolates. A panel of biomarkers that represent pro-/anti-inflammatory, pro-/anti-apoptotic, and anti-bacteria/viral responses of the fish should be taken into consideration when evaluating the usefulness of the potential probiotic in aquaculture.

Differential innate immune response of European seabass (Dicentrarchus labrax) against Streptococcus iniae

Streptococcus iniae is a Gram-positive bacteria that causes invasive infections with severe septicemia and meningitis, producing high economic losses in marine and continental aquaculture. Head kidney leukocytes of European sea bass (Dicentrarchus labrax) were used to measure the differential innate immune response upon infection with S. iniae. The complete inhibition in the production of intracellular superoxide radicals and total peroxidase content was observed in infected cells. This study also elucidates changes in the relative expression of some immune-related genes. Interleukin 1β, tumor necrosis factor-α and interleukin-6 reached a peak of expression at 4-8 h post-infection, subsequently decreasing significantly up to 48 h post-infection. However, interleukin-10 and Mx protein increased over time, reaching the pick of expression at 48 h post-infection, whereas caspase-3 showed down regulation until 48 h post-infection. The in vivo study of immune related genes show the same kinetics of mRNAs expression as in vitro experience. The proinflammatory cytokines mRNA transcription levels peaked at an earlier time in vivo than in vitro system. Our findings indicate that there is a direct relationship between the dissemination of bacteria and the resulting infection-associated inhibition of respiratory burst, apoptosis, and the pro- and anti-inflammatory gene expression profiles.

Immunization of sea bream (Sparus aurata) juveniles against Photobacterium damselae subsp. piscicida by short bath: Effect on some pro-inflammatory molecules and the Mx gene expression

Cytokines are a family of proteins derived from macrophages, lymphocytes, granulocytes, mast cells and epithelial cells and can be divided into interferons (IFNs), Interleukins (ILs) and Tumor Necrosis factors (TNFs) among others. The presence of cytokines in a wide number of fish species has been proved and several molecules types have been already cloned and sequenced. In this work some proinflamatory molecules and Mx gene were detected in the liver of vaccinated sea bream juveniles with an average body weight of 5 g. The method of immunization was by short bath and three different bacterins against the marine pathogen Photobacterium damselae subsp. piscicida were designed and used to immunize fish. Five genes encoding for five different molecules were analyzed by real time PCR: IL-1β, IL Ir-2, Cox-2, Mx and TNFα. Gene expression was quantified along four days after fish immunization and results were compared among groups. Results show that the heat-inactivated vaccine stimulates the up-regulation of IL-1β, IL Ir-2, Cox-2 and TNFα genes whereas the UV-light inactivated vaccine was the unique vaccine which stimulates the expression of Mx gene. The present is a novel study that shows by the first time the effect of the inactivation process of vaccines on the expression levels of genes involved in the defense against Photobacterium damselae subsp piscicida.

Disease resistance and immune-relevant gene expression in golden mandarin fish, Siniperca scherzeri Steindachner, infected with infectious spleen and kidney necrosis virus-like agent

Infectious spleen and kidney necrosis virus (ISKNV), family Iridoviridae, genus Megalocytivirus, may cause high mortality rates such as those seen in mandarin fish, Siniperca chuatsi. ISKNV has attracted much attention due to the possible environmental threat and economic losses it poses on both cultured and wild populations. We have investigated the pathogenicity of ISKNV-like agent Megalocytivirus, isolated from infected pearl gourami, in golden mandarin fish, Siniperca scherzeri - a member of the Percichthyidae family - and in another Percichthyidae species, S. chuatsi. Fish were challenged with four different doses of ISKNV-like agent Megalocytivirus (1, 10, 100 or 1000 μg per fish) over a 30-day period, and cumulative fish mortalities were calculated for each group. No significant mortality was observed for fish challenged with the lowest dose (1 μg per fish) relative to a control group. However, all other challenged groups showed 100% mortality over a 30-day period in proportion to the challenge dose. Quantitative real-time PCR was performed to measure mRNA expression levels for six immune-related genes in golden mandarin fish following ISKNV-like agent challenge. mRNA expression levels for IRF1, Mx, viperin and interleukin 8 significantly increased, while mRNA levels for IRF2 and IRF7 remained constant or declined during the challenge period.

Vibrio anguillarum bacterin uptake via the gills of Japanese flounder and subsequent immune responses

The mucosal surfaces of fish allow for the introduction of foreign substances, including antigens, from the surrounding environment. In this study, uptake of Vibrio anguillarum J-O-3 serotype bacterin by Japanese flounder, and the subsequent immune responses were investigated. Immunohistochemistry revealed that the bacterin was taken up through the epithelial cells of gills. The transcription levels of inflammatory cytokines such as interleukin (IL)-1β, IL-6 and tumor necrosis factor α were significantly up-regulated in the gills at 3 days following exposure to the bacterin. There was also a corresponding increase in IL-8 receptor, CD4-1, CD4-2 and CD8α transcript levels in the gills. Our findings suggest that the gills play a major role in the uptake of V. anguillarum bacterin and induction of inflammation, which results in an activation of the adaptive immune response in teleost fish.

Cytokine expression in head-kidney leucocytes of European sea bass (Dicentrarchus labrax L.) after incubation with the probiotic Vagococcus fluvialis L-21

The European sea bass (Dicentrarchus labrax L.) is one of the most extensively farmed marine fish in the Mediterranean sea. Under the high-density condition, common in aquaculture, the infectious diseases can cause significant economic losses. Probiotics are presented as an alternative to antibiotics for the control of aquaculture diseases. This study used real-time PCR to investigate in vitro the dynamic of expression of immune-related genes in sea bass after incubation with live and inactivated (heat and Uv-light) probiotic Vagoccus fluvialis L-21 at different times (T1, T12, T24, T48). The immune associated genes, interleukin-1 (IL-1), interleukin-6 (IL-6), interleukin 10 (IL-10), TumourTumour necrosis factor- (TNF-), ciclo-oxigenase-2 (COX-2), caspase-3 (Casp-3) and Mx were studied in head-kidney (HK) leucocytes of sea bass after incubation with the probiotic strain. Transcript of proinflammatory cytokines (IL-1, TNF-, COX-2) was highly up-regulated after 1 h of incubation with the probiotic strain V. fluvialis L-21. We found statistically significant difference in pick of expression of TNF-, after 1 h of incubation with Uv-light inactivated probiotic strain. The COX-2 expression was highly up-regulated at all times studied, with the exception of 12 and 24 h post incubation for the Uv-light inactivated bacteria. Transcript of IL-10 and Casp-3 showed the higher statistically significant differences of expression after 48 h post incubation with live bacteria. In the contrast, sea bass HK leucocytes expressed Mx at 12 and 48 h without statistically differences among treatments. Our results suggest that V. fluvialis L-21 is able to stimulate in vitro some immune-related genes associated with the early inflammatory response. Future studies in vivo are necessary to clarify this process in sea bass.

Molecular cloning, subcelluar location and expression profile of signal transducer and activator of transcription 2 (STAT2) from turbot, Scophthalmus maximus

Signal transducer and activator of transcription 2 (STAT2) is an important molecule involved in the type I interferon signalling pathway. To date, little STAT2 homologue is available in fish except Atlantic salmon and goldfish. In this paper, STAT2 was firstly cloned and characterized from turbot, a marine flatfish with high economic value. Briefly, turbot STAT2 cDNA is 3206 bp in length encoding a predicted protein of 793 amino acids. The phylogenetic tree shows that turbot STAT2 protein shared the closest relationship with Atlantic salmon. Analysis of subcellular distribution indicates that STAT2 is mainly present in the cytoplasm of TK cells. Stat2 mRNA is constitutively expressed in widespread tissues and induced by several folds in turbot tissues and TK cells after stimulation with Vibrio anguillarum and lymphocystis disease virus (LCDV). Unlike the higher vertebrate STAT2, turbot STAT2 nuclear export signal (NES) exists not in the C-terminal 79 amino acids but in N-terminal 137-312 amino acids (STAT_alpha domain). The nuclear translocation of turbot STAT2 after Poly(I:C) treatment proved its transcription activity in TK cells. All these results suggested that STAT2 may be involved in the immune response in turbot as a transcription factor.

Proteomic characterization of the acute-phase response of yellow stingrays Urobatis jamaicensis after injection with a Vibrio anguillarum-ordalii bacterin

Systemic inflammatory responses of mammals and bony fish are primarily driven by coordinated up-regulation and down-regulation of plasma acute-phase proteins. Although this general principle is believed to be universal among vertebrates, it remains relatively unexplored in elasmobranchs. The objective of this study was to characterize acute changes in the plasma proteome of three yellow stingrays Urobatis jamaicensis following intraperitoneal injection with a commercial Vibrio bacterin. Changes in plasma protein levels were analyzed immediately prior to vaccination (time 0) and at 24 and 72 h post-injection by isobaric tags for relative and absolute quantitation (iTRAQ 4-plex) using shotgun-based nano liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis and de novo peptide sequencing. Pooled 2D-LC-MS/MS and de novo sequencing data revealed differential expression of 156 distinct plasma proteins between time 0 and at least one post-vaccination time point. Using 1.5-fold change in expression as physiologically significant, 14/156 (9.0%) proteins were upregulated in at least one stingray through at least one experimental timepoint. Upregulated proteins included complement factors, Mx-protein, hemopexin, factor X and prothrombin. Seventy-six of 156 (48.7%) proteins were downregulated in the acute-phase response, including transferrin, apolipoprotein B, heparin cofactor 2, alpha2-macroglobulin, and various growth factors. Other differentially upregulated or downregulated proteins included intracellular, cell binding and structural proteins, proteins involved in physiologic processes, and unknown/hypothetical proteins. Selected bioactive factors are discussed for their putative roles in the elasmobranchs acute-phase response. These findings contribute to our understanding of disease processes in elasmobranchs, immunologic phylogeny in vertebrates, and begin the search for potential biomarkers of disease in these ecologically important fish.

Concurrent injection of a rhabdovirus-specific DNA vaccine with a polyvalent, oil-adjuvanted vaccine delays the specific anti-viral immune response in Atlantic salmon, Salmo salar L

Vaccines are commonly used in salmonid aquaculture as a method of disease prevention. Although there is a substantial amount of published research regarding the immunological and physiological effects following the injection of different polyvalent vaccines and DNA vaccines, there are no published reports examining the physiological and immunological effects of concurrent vaccine injection, which is the situation encountered in aquaculture. Using key immunological parameters such as lysozyme activity and specific antibody titres we examined the short-term activation of the immune response of cultured Atlantic salmon (Salmo salar L.) following concurrent injection with a traditional, polyvalent, oil-adjuvanted vaccine (AV) and an IHNV-specific DNA vaccine (DV). Our results indicate that different aspects of the innate and adaptive immune responses are influenced in either a positive or negative manner. While concurrent vaccine injection elicited an increase in lysozyme activity, changes in antibody titre (Ab) were antigen specific. The production of anti-Aeromonas salmonicida Abs was significantly greater in the combined vaccine group at 296 degree days post-vaccine injection (dd pvi), while the production of anti-Listonella anguillarum Abs was significantly greater at 106 dd pvi in the combined vaccine group. Of even greater interest was the apparent delay in production of IHNV-specific neutralizing antibodies (NAb) when the DV was injected concurrently with the polyvalent AV. The results indicated that concurrent injection of a polyvalent oil-AV and a DV can be beneficial to the production of antibodies; however, the specific anti-viral response may be delayed.

The association between metabolic rate, immune parameters, and growth performance of rainbow trout, Oncorhynchus mykiss (Walbaum), following the injection of a DNA vaccine alone and concurrently with a polyvalent, oil-adjuvanted vaccine

This research demonstrates a significant increase in routine metabolic rate (RMR) following injection of a DNA vaccine concurrently with a polyvalent, oil-adjuvanted vaccine. The increase in RMR was transient and associated with increased activity of both the non-specific and specific immune responses. Rainbow trout (Oncorhynchus mykiss) were injected with a DNA vaccine (DV), a commercially available polyvalent, oil-adjuvanted vaccine (AV), or the two vaccines in combination and sampled at 203, 305, and 406 days (dd) post-vaccine injection (pvi) for RMR and key immune parameters (serum lysozyme activity, serum neutralization antibody titres). The RMR of fish that received both the DV and the AV was significantly higher at 203 dd pvi, compared to fish from all other treatment groups which included the control, the AV, and the DV groups. The increased RMR corresponded to elevated levels of serum lysozyme activity and an earlier seroconversion of virus-specific neutralizing antibodies. To determine if growth performance was affected by the transient increase in RMR, specific growth rate (SGR), percent daily weight gain (WG), and feed conversion ratio (FCR) were determined at 798, 1204, and 1610 dd pvi. Although fish in all three vaccine groups showed significant increases in SGR and WG at 798 and 1610 dd pvi compared to the control group, the overall weight of the fish was not different at the end of the experiment. In summary, this study shows that concurrent injection of a DV and an AV transiently increases the RMR of rainbow trout and changes the manner in which the immune response occurs, but does not affect the overall growth performance of the fish.

Expression of interferon and interferon-induced genes in salmonids in response to virus infection, interferon-inducing compounds and vaccination

Interferons (IFNs) involved in innate immunity against viruses have recently been cloned from Atlantic salmon and rainbow trout. Moreover, several IFN-stimulated genes (ISGs) have been cloned from salmonids although only Mx has been shown to possess antiviral properties. Much less in known about how viruses induce IFNs in salmonids, but synthetic ligands for some of the main mammalian viral sensors also induce IFNs and ISGs in salmonids. Analysis of the promoters of the salmon IFN-alpha1 and IFN-alpha2 genes shows that activation is dependent on both NFkappaB and IRFs similar to human IFN-beta. Furthermore, several IFN-stimulated genes (ISGs) have been cloned from salmonids although only Mx has been shown to possess antiviral properties. The synthetic compounds poly I:C, imidazoquinolines and CpG oligonucleotides induce IFNs and ISGs in salmonids, probably through the same pathways as in mammals. Salmonid viruses show potent ability to stimulate expression of IFN and ISGs in vivo. Differences between viruses in the ability to stimulate host gene expression are often more evident in cell culture, but more work is needed to pinpoint how salmonid viruses antagonize the IFN system of their host. Finally, existing data suggest that IFNs play a role in the early non-specific protection observed after vaccination of salmonids with rhabdoviral DNA vaccines and conventional polyvalent vaccines.

Serum CRP-like protein profile in common carp Cyprinus carpio challenged with Aeromonas hydrophila and Escherichia coli lipopolysaccharide

The potential of C-reactive protein (CRP)-like proteins to be used as a biomarker of health status in cultured carp obtained from various European fish lines has been assessed. Varying CRP-like protein levels in the serum of carp were monitored using an indirect competitive enzyme-linked immunosorbent assay. CRP-like protein basal levels in normal fish varied between carp lines, ranging on average from 2.9+/-0.15 to 12.57+/-1.19 microg ml(-1). Serum levels of CRP-like protein in carp were observed to increase several fold in fish infected with the pathogen Aeromonas hydrophila. However, carp injected with Escherichia coli lipopolysaccharide (LPS) serotype 0111:B4 did not exhibit an increase in CRP-like proteins levels.

Functional genomic analysis of the response of Atlantic cod (Gadus morhua) spleen to the viral mimic polyriboinosinic polyribocytidylic acid (pIC)

In order to improve our understanding of how Atlantic cod (Gadus morhua) respond to viruses, we characterized immune-related gene expression in spleen tissues following stimulation with a synthetic double-stranded RNA polyriboinosinic polyribocytidylic acid (pIC). We used reciprocal suppression subtractive hybridization (SSH) cDNA libraries and quantitative RTPCR (QPCR) to identify and quantify pIC-responsive transcripts. A total of 3874 expressed sequence tags (ESTs) were generated from SSH libraries enriched for genes responsive to pIC. Thirteen immune-relevant genes from the libraries were subjected to QPCR. Genes confirmed as up-regulated by pIC included interferon stimulated gene 15, a small inducible cytokine, interferon regulatory factors (1, 7, and 10), MHC class I, viperin, and ATP-dependent helicase LGP2. Alpha-1-microglobulin (bikunin) was down-regulated, suggesting that pIC may suppress the acute phase response. Since the SSH libraries built for this study identified genes involved in the antiviral response, they are important resources for studying the responses of Atlantic cod to viruses. Evidence is provided for the existence of a RIG-I-like RNA helicase viral recognition pathway in Atlantic cod. Taken together, our data show that Atlantic cod can recognize double-stranded RNA and mount a rapid and potent interferon pathway response that is similar to that observed in other fish species and higher vertebrates.

Total substitution of fish oil by vegetable oils in gilthead sea bream (Sparus aurata) diets: effects on hepatic Mx expression and some immune parameters

The use of vegetable oils in fish nutrition has been extensively studied; and recent work has focused attention on replacing fish oil with alternative fatty acid sources and their effect on the immune system. However, little is known about the effect of these oils on immune parameters such as the fish interferon system. In this study we evaluate the effect of two vegetable oils (linseed and soybean) on gilthead sea bream Mx expression and other innate immune parameters. Experimental diets were formulated where fish oil was totally replaced by vegetable oils or for a mixture of them (50% linseed and 50% soybean). Another diet prepared with pure fish oil was used as a control. Two experiments were carried out in order to evaluate growth, feed utilization, serum alternative complement pathway activity, serum lysozyme and phagocytic activity of head kidney leucocytes as well as Mx expression in the liver. In the first experiment fish were fed with experimental diets for 6 months and then, growth and feed utilization as well as immune parameters were analyzed. In the second experiment, fish from the previous feeding trial were injected with either a sub-lethal dose of Photobacterium damselae subsp. piscicida (94/99) or a synthetic dsRNA (Poly I:C) in order to stimulate an Mx response. The results show that total substitution of fish oil by vegetable oils decreased the growth of gilthead sea bream juveniles. Furthermore, both phagocytic activity and serum alternative complement pathway activity were significantly reduced by the inclusion of either vegetable oil individually in the sea bream diets, but the diet with mixed vegetable oils had no significant effect. There was no effect on serum lysozyme levels but the basal constitutive levels of Mx transcript expression in the liver were elevated in the fish fed the vegetable oil diets. The time-course of the Mx response to injection of Poly I:C was shorter in the fish fed the fish oil diet and the fish fed the diet based on a mixture of both vegetable oils showed a faster Mx response to bacterial injection. Following stimulation with Poly I:C or PDP the fish fed the vegetable oil based diets still maintained higher basal levels of hepatic Mx expression than the fish fed the fish oil diet which returned to undetectable levels.

Isolation of a novel fish thymidylate kinase gene, upregulated in Atlantic salmon (Salmo salar L.) following infection with the monogenean parasite Gyrodactylus salaris

Analysis of differential gene expression in salmon (Salmo salar) blood following infection with the monogenean parasite Gyrodactylus salaris, resulted in the isolation of a thymidylate kinase gene not previously described from fish and which showed similarity to an LPS-inducible thymidylate kinase gene isolated from mouse macrophages. This salmon TYKi-like gene may play a role in an innate generalised response to pathogen infection as it was upregulated in salmon following infection with the parasite, and also in response to injection with the immunostimulants LPS and Poly I:C, used to emulate bacterial and viral infections, respectively. The possible role of this gene in the biosynthesis of mitochondrial DNA in activated macrophages, in response to G. salaris infection is discussed.

Cloning of the glucocorticoid receptor (GR) in gilthead seabream (Sparus aurata). Differential expression of GR and immune genes in gilthead seabream after an immune challenge

In order to determine the cortisol response after an immune challenge in the gilthead seabream (Sparus aurata), a cortisol receptor (GR) was cloned, sequenced and its expression determined after lipopolysaccharide (LPS) treatment. To clone the gilthead seabream GR (sbGR), consecutive PCR amplifications and screening of a pituitary cDNA library were performed. We obtained a clone of 4586 bp encoding a 784aa protein. Northern blot analysis from head kidney, heart and intestine revealed that the full length sbGR mRNA was approximately 6.5 Kb. A LPS treatment, used as an acute stress model, was employed to characterise the expression of sbGR and some selected genes involved in the immune response (IL-1beta, TNF-alpha, Mx protein, cathepsin D and PPAR-gamma). All genes were expressed in all tissues examined and responses were tissue and time dependent revealing differential gene expression profiles after LPS administration. Furthermore, analysis of plasma cortisol levels after LPS injection, showed an acute response to inflammatory stress with a significant increase two and six h after injection, recovering to basal levels 12 h post-stress in all LPS concentrations tested.

Quantitative expression (Walbaum) of immunological factors in rainbow trout, Oncorhynchus mykiss (Walbaum), after infection with either Flavobacterium psychrophilum, Aeromonas salmonicida, or infectious haematopoietic necrosis virus

To further enhance our understanding of immunological gene expression in rainbow trout, Oncorhynchus mykiss, after infection with naturally occurring pathogens, a series of probes and primers were developed for the quantification of immune factors. Separate groups of specific-pathogen-free rainbow trout were infected with either Flavobacterium psychrophilum, Aeromonas salmonicida or infectious haematopoietic necrosis virus (IHNV). Three different concentrations of each pathogen were used and samples from infected and mock-infected fish were taken at either 1 or 5 days after infection. Ten fish were sampled at each time point for individual sections of liver, spleen and head kidney. Organ specimens from five of the fish were used to re-isolate and quantify the pathogen at the time the samples were taken. Total RNA was extracted from the organs of the remaining five animals. Using real-time polymerase chain reaction with fluorescent-labelled probes, the RNA from these organs was examined for the level of expression of the following immunological factors; an interferon related protein (MX-1), interleukin-8 (IL-8), the cytotoxic T-cell marker CD-8 and complement factor C3 (C3). They were also measured for the level of beta-actin, which was used as a standardization control for cellular RNA expression. Infection with IHNV produced the greatest change in expression level for all the immunological related factors examined in this study. IHNV elicited the best dose response profile, which was typically seen at 5-days post-infection for MX-1, C3, IL-8 and CD-8. Infection with A. salmonicida and F. psychrophilum showed elevated, but variable expression levels for several of the genes tested.

Expression profiling and validation of reference gene candidates in immune relevant tissues and cells from Atlantic salmon (Salmo salar L.)

The expression levels of three commonly used housekeeping genes, EF1-alpha, RPS20 and Beta-Actin, were examined in seven different tissues and leucocytes from non-stimulated Atlantic salmon (Salmo salar L.). The tissues analysed by quantitative real-time PCR were gill, liver, intestine, muscle, spleen, head kidney leucocytes (HKL) and peripheral blood leucocytes (PBL). The experiments were performed to investigate the transcriptional stability within and between tissues and leucocytes and between individuals. For all tissues and leucocytes, an appropriate reference gene was identified except for muscle tissue. HKL were used as a calibrator and the expression of EF1-alpha varied maximally 2.5-fold in five out of the six tissues and leucocytes investigated relative to the expression of 18S rRNA. The RPS20 gene was more intermediate and varied at least by a factor of two and maximally by a 20-fold factor. Beta-Actin was generally the most regulated gene showing high variations for gill (5.8x) and spleen tissue (10.3x) relative to the calibrator. A suitable reference gene for muscle tissue was not found since the expression varied between 8.3- and 25-fold for the three genes compared to the calibrator. By comparing the expression results of the non-stimulated tissues and leucocytes using the Normfinder programme, it was further shown that EF1-alpha was the most stably expressed gene both between individuals and the different tissues/leucocytes. Stimulation with lipopolysaccharide (LPS) of TO cells and HKL from Atlantic salmon was additionally performed to reveal whether an immune stimulating agent would change the expression level of EF1-alpha, RPS20 and Beta-Actin. LPS stimulation of cells revealed that RPS20 and EF1-alpha were least regulated by the LPS treatment in the TO cells relative to 18S rRNA, but in HKL, Beta-Actin was the most appropriate gene. However, the variations were overall maximally two-fold in LPS-stimulated TO cells and HKL, which make all three genes suitable as reference genes in this case. A further experiment showed that no RT- and/or PCR inhibitors were present in the non-stimulated tissues and cells, indicating true transcriptional differences.

Cloning of an orange-spotted grouper (Epinephelus coioides) Mx cDNA and characterisation of its expression in response to nodavirus

Molecular cloning and nucleotide sequencing of cDNA encoding an orange-spotted grouper (Epinephelus coioides) homolog of Mx ("OsgMx") was conducted and its possible role in fish immunity was analysed. Similar to mammalian Mx, the OsgMx are members of a family of interferon-inducible genes that are expressed by cells in response to nodavirus and iridovirus naturally-infected. Expression of OsgMx mRNA was noticeably upregulated in all tissues by nodavirus naturally-infected grouper. The transcription of OsgMx gene increased 6 h after intramuscular injection of nodavirus experimentally-infected fish and peaked at 72 h in their brains. Analysis of the 5'-flanking sequence of the gene shows that as in pufferfish and zebrafish, the OsgMx promoter contains two potential interferon-stimulated response element (ISRE) responsible for the induction of interferon-inducer polyinosinic-polycytidylic acid (Poly[I:C]). Transient transfection of grouper cells in gfp-reporter gene assays shows that the activation of the grouper Mx promoter fragment by Poly[I:C] is sufficient to allow the expression of green fluorescent protein (GFP). These results may provide a possible regulated pathway against nodavirus.

Expression profiles of inflammatory and immune-related genes in Atlantic salmon (Salmo salar L.) at early time post vaccination

Vaccination of Atlantic salmon parr with oil-based vaccines will inevitably cause inflammation at the site of injection, albeit the underlying mechanisms are not very well understood or studied in any detail. Here, we report time-course changes in expression levels, assessed by real-time RT-PCR of IL-1 beta, Mx, two beta-2-microglobulin variants and MHC class II beta, from 2 to 19 days post vaccination with a multi-component oil-adjuvanted vaccine. Highly variable individual responses to vaccination make selection of high responders essential prior to subtractive analysis. Based on the above mentioned expression profiles, high-responding individuals at 2, 8 and 19 days post vaccination, were selected for subtractive analysis. Clustering of clones according to putative function, suggest an initial up-regulation of genes involved in metabolism and cell signalling, before onset of genes involved in inflammation. The lag-time for genes considered as inflammatory markers was more than 48 h, while they were found to constitute the major part of up-regulated transcripts by 8 days post vaccination. By day 19, immune-related genes like immunoglobulin and T cell-receptor genes, comprised a higher proportion of the up-regulated genes than at earlier time points.