Co-injection of interleukin 8 with the glycoprotein gene from viral haemorrhagic septicemia virus (VHSV) modulates the cytokine response in rainbow trout (Oncorhynchus mykiss)

Inflammatory response of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) larvae against Ichthyophthirius multifiliis

At hatching, the immune system of the rainbow trout larva is not fully developed. The larva emerges from the egg and is exposed to the aquatic freshwater environment containing pathogenic organisms. At this early stage, protection from disease causing organisms is thought to depend on innate immune mechanisms. Here, we studied the ability of young post-hatch rainbow trout larvae to respond immunologically to an infection with Ichthyophthirius multifiliis and also report on the localization of 5 different immune relevant molecules in the tissue of infected and uninfected larvae. Quantitative RT-PCR (qPCR) was used to analyze the genetic regulation of IL-1β, IL-8, IL-6, TNF-α, iNOS, SAA, cathelicidin-2, hepcidin, IL-10, IL-22, IgM and IgT. Also, a panel of 5 monoclonal antibodies was used to investigate the presence and localization of the proteins CD8, SAA, MHCII, IgM and IgT. At 10 days (84 degree days) post-hatching, larvae were infected with I. multifiliis and sampled for qPCR at 3, 6, 12, 24, 48 and 72 h post-infection (p.i.). At 72 h p.i. samples were taken for antibody staining. The first of the examined genes to be up-regulated was IL-1β. Subsequently, IL-8 and cathelicidin-2 were up-regulated and later TNF-α, hepcidin, IL-6, iNOS and SAA. Immunohistochemical staining showed presence of CD8 and MHCII in the thymus of both infected and non-infected larvae. Staining of MHCII and SAA was seen at sites of parasite localization and weak staining of SAA was seen in the liver of infected larvae. Staining of IgT was seen at site of infection in the gills which may be one of the earliest adaptive factors seen. No positive staining was seen for IgM. The study illustrates that rainbow trout larvae as young as 10 days (84 degree days) post-hatch are able to regulate important immune relevant cytokines, chemokines and acute phase proteins in response to infection with a skin parasitizing protozoan parasite.

Transcriptomic and physiological responses to fishmeal substitution with plant proteins in formulated feed in farmed Atlantic salmon (Salmo salar)

BACKGROUND

Aquaculture of piscivorous fish is in continual expansion resulting in a global requirement to reduce the dependence on wild caught fish for generation of fishmeal and fish oil. Plant proteins represent a suitable protein alternative to fish meal and are increasingly being used in fish feed. In this study, we examined the transcriptional response of Atlantic salmon (Salmo salar) to a high marine protein (MP) or low fishmeal, higher plant protein replacement diet (PP), formulated to the same nutritional specification within previously determined acceptable maximum levels of individual plant feed materials.

RESULTS

After 77 days of feeding the fish in both groups doubled in weight, however neither growth performance, feed efficiency, condition factor nor organ indices were significantly different. Assessment of histopathological changes in the heart, intestine or liver did not reveal any negative effects of the PP diet. Transcriptomic analysis was performed in mid intestine, liver and skeletal muscle, using an Atlantic salmon oligonucleotide microarray (Salar_2, Agilent 4x44K). The dietary comparison revealed large alteration in gene expression in all the tissues studied between fish on the two diets. Gene ontology analysis showed, in the mid intestine of fish fed PP, higher expression of genes involved in enteritis, protein and energy metabolism, mitochondrial activity/kinases and transport, and a lower expression of genes involved in cell proliferation and apoptosis compared to fish fed MP. The liver of fish fed PP showed a lower expression of immune response genes but a higher expression of cell proliferation and apoptosis processes that may lead to cell reorganization in this tissue. The skeletal muscle of fish fed PP vs MP was characterized by a suppression of processes including immune response, energy and protein metabolism, cell proliferation and apoptosis which may reflect a more energy efficient tissue.

CONCLUSIONS

The PP diet resulted in significant effects on transcription in all the 3 tissues studied. Despite of these alterations, we demonstrated that high level of plant derived proteins in a salmon diet allowed fish to grow with equal efficiency as those on a high marine protein diet, and with no difference in biometric quality parameters.

Immune responses of zebrafish (Danio rerio) induced by bath-vaccination with a live attenuated Vibrio anguillarum vaccine candidate

A fish vaccine candidate, live attenuated Vibrio anguillarum, which can protect fish from vibriosis, was established in our laboratory. In this study, the protective immunological mechanism of live attenuated V. anguillarum was investigated in zebrafish as a model animal. After bath-vaccinated with the live attenuated strain, zebrafish were challenged with wild pathogenic strain to test the immunoprotection of the live attenuated strain. As the results, specific antibody response of fish against V. anguillarum was found to gradually increase during 28 days post-vaccination, and remarkable protection was showed with a high relative protection survival (RPS) of about 90%. Moreover, the vaccination changed the expressions of several immune-related genes in the spleens and livers of zebrafish. Among them, the expressions of pro-inflammatory factors such as IL-1 and IL-8 were tenderly up-regulated with about 3-4 fold in 1-7 days post-vaccination, while MHC II rose to a peak level of 4-fold in 7th day post-vaccination. These results gave some important messages about the mechanism of specific protection induced by live attenuated V. anguillarum and showed the availability of zebrafish model in the evaluation of the vaccine candidate.

Pro-inflammatory functions of carp CXCL8-like and CXCb chemokines

Numerous CXC chemokines have been identified in fish, however, their role in inflammation is not well established. Here, CXC chemokines of the CXCL8-like (CXCa_L1 and CXCL8_L2) and CXCL9/10/11-like (CXCb) subset were investigated in carp. Recombinant CXCa_L1, CXCL8_L2 and CXCb all stimulated chemotaxis of macrophages and granulocytes in vitro. CXCb also attracted lymphocytes. Distinct effects on phagocyte activation were observed: the CXCL8-like chemokines increase respiratory burst activity, but not nitrite production. The three chemokines differentially induced a moderate increase in IL-1β, CXCa_L1 and CXCL8_L2 gene expression. Intracellular calcium mobilization in granulocytes upon CXCa_L1 stimulation implies signal transduction through G-protein coupled CXC receptors. Notably, upon intraperitoneal administration, carp CXCL8-like chemokines strongly induced in vivo leukocyte recruitment, including neutrophils and monocytes/macrophages, in contrast to CXCb, for which the number of recruited leukocytes was low. The results indicate functional homology for carp CXCL8-like and CXCb chemokines with mammalian CXCL8 and CXCL9-11, respectively.

Chemokines in teleost fish species

Chemokines are chemoattractant cytokines defined by the presence of four conserved cysteine residues which in mammals can be divided into four subfamilies depending on the arrangement of the first two conserved cysteines in their sequence: CXC (α), CC (β), C and CX(3)C classes. Evolutionarily, fish can be considered as an intermediate step between species which possess only innate immunity (invertebrates) and species with a fully developed acquired immune network such as mammals. Therefore, the functionality of their different immune cell types and molecules is sometimes also intermediate between innate and acquired responses. The first chemokine gene identified in a teleost was a rainbow trout (Oncorhynchus mykiss) chemokine designated as CK1 in 1998. Since then, many different chemokine genes have been identified in several fish species, but their role in homeostasis and immune response remains largely unknown. Extensive genomic duplication events and the fact that chemokines evolve more quickly than other immune genes, make it very difficult to establish true orthologues between fish and mammalian chemokines that would help us with the ascription of immune roles. In this review, we describe the current state of knowledge of chemokine biology in teleost fish, focusing mainly on which genes have been identified so far and highlighting the most important aspects of their expression regulation, due to the great lack of functional information available for them. As the number of chemokine genes begins to close down for some teleost species, there is an important need for functional assays that may elucidate the role of each of these molecules within the fish immune response.

Toll-like receptors and interferon associated immune factors in viral haemorrhagic septicaemia virus-infected olive flounder (Paralichthys olivaceus)

Pattern recognition receptor (PRR) toll-like receptors (TLRs), antiviral agent interferon (IFN) and the effector IFN stimulated genes (ISGs) play pivotal role in antiviral innate immunity of a host. The present in-vivo experiment was conducted to investigate the role of these innate immune factors in early phase as well as during recovery of viral haemorrhagic septicaemia virus (VHSV) infection by quantitative real-time reverse transcriptase polymerase chain reaction. A less lethal VHSV infection was generated in olive flounder (Paralichthys olivaceus) and was sampled at 3, 6, and 12h post infection (hpi), and 1, 2, 4, and 7 days post infection (dpi). At 3 hpi, the VHSV N gene was detected in three out of five fish and all five fish showed a relative fold increase of TLR 2, TLR 7, interleukin 8 (IL 8), IFN regulatory factor 3 (IRF 3), IRF 7, and ISG 15. Viral copies rapidly increased at 12 hpi then remained high until 2 dpi. When viral copy numbers were high, a higher expression of immune genes IL 1β, IRF 3, IRF 7, Type I IFN, ISG 15 and Mx was observed. Viral copies were drastically reduced in 4 and 7 dpi fish, and also the immune response was considerably reduced but remained elevated, except for ISG 15 which found equal to control in 7 dpi fish. A high degree of correlation was observed between immune genes and viral copy number in each of the sampled fish at 12 hpi. A fish with ascites sampled at 7 dpi displayed high viral copy but under-expressed immune genes except for Mx. When viral copies were high at 1 and 2 dpi, both TLR 2 and TLR 7 were down-regulated, perhaps indicating immune suppression by the virus. The quick and prolonged elevated expression of the immune genes indicates their crucial role in survival of host against VHSV.

Association between Yersinia ruckeri infection, cytokine expression and survival in rainbow trout (Oncorhynchus mykiss)

The immune response against bacterial pathogens has been widely studied in teleosts and it is evident that survival chances differ significantly within a host population. Identification of indicators for susceptibility and responsiveness will improve our understanding of this host-pathogen interaction. The present work shows that the transcripts of cytokine genes in blood cells sampled three days post-infection was significantly higher in fish which obtained a high bacteriemia and died at later time points when compared to both non-infected control fish and infected fish that survived the infection. Rainbow trout were infected by bath challenge in a bacterial suspension (LD(60) dose, 1.8 × 10(9) CFU/ml Yersiniaruckeri for 1 h) and subsequently transferred to individual aquaria for 30 days of observation. Blood samples were analyzed for presence of Y. ruckeri both by culture and quantitative RT real-time PCR (qRT-PCR) and transcript levels of 28 genes encoding molecules which are important in the immune response. The transcript levels of a number of central cytokines, chemokines and cytokine receptors (IL-1β, IL-6, IL-8, IL-10, TNF-α, IL-receptor II) were significantly increased in infected fish that died later. In addition, a significantly higher amount of Y. ruckeri was found in the blood of the fish that died when compared to survivors. The study indicates that highly susceptible trout obtain an early heavy septicemia infection, which elicits a high up-regulation of the transcript of pro-inflammatory cytokines. Thus, less susceptible fish are protected by other factors and contract merely a weak non-lethal infection eliciting no or a weak cytokine response.

Cellular and molecular immune responses of the sea bass (Dicentrarchus labrax) experimentally infected with betanodavirus

Naïve sea bass juveniles (38.4 + or - 4.5 g) were intramuscularly infected with a sublethal dose of betanodavirus isolate 378/I03, followed after 43 days by a similar boosting. This infection resulted in an overall mortality of 7.6%. At various intervals, sampling of fish tissues was performed to investigate: i) B and T lymphocyte content in organs and tissues; ii), proliferation of leucocytes re-stimulated in vitro with inactivated virus; iii) presence of serum antibody specific for betanodavirus; iv) expression of genes coding for the following immunoregulatory molecules involved in innate and acquired responses: type I IFN, Mx, IL-1, Cox-2; IL-10, TGF-beta, TCRbeta, CD4, CD8alpha, IgM, by using a quantitative PCR array system developed for sea bass. The obtained results showed a detectable increase of T cells and B cells in PBL during betanodavirus infection. Furthermore, leucocytes obtained from blood, head kidney, and gills showed a detectable "in vitro" increase in viability upon addition of inactivated viral particles, as determined by measuring intracellular ATP concentration. ELISA analysis of sera showed that exposure to nodavirus induced a low, but specific antibody titer measured 43 days after infection, despite the presence of measurable levels of natural antibody. Finally, a strong upregulation of genes coding for type I IFN, Mx, and IgM was identified after both infection and boosting. Interestingly, an upregulation of Cox-2 until boosting, and of TGF-beta and IL-10 after boosting was also observed, while the other tested genes did not show any significant variations with respect to mock-treated fish. Overall, our work represents a first comprehensive analysis of cellular and molecular immune parameters in a fish species exposed to a pathogenic virus.

Chemokine transcription in rainbow trout (Oncorhynchus mykiss) is differently modulated in response to viral hemorrhagic septicaemia virus (VHSV) or infectious pancreatic necrosis virus (IPNV)

Chemokines not only act as chemoattractants for immune cells, but also exert immunomodulatory actions, thus modulating the immune functions of their target cells. In rainbow trout (Oncorhynchus mykiss), twenty-four chemokines have been identified to date. Even though their sequences have been reported, their biological role has been scarcely elucidated and the role that these chemokines have on the antiviral response in fish has been poorly studied. In this sense, in the current work, we have determined the levels of expression of several of these rainbow trout chemokines (CXCd, gammaIP, CK1, CK3, CK5B, CK6, CK7A, CK9 and CK12) in head kidney and spleen during the course of a viral infection using two different viruses, viral hemorrhagic septicaemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV), comparing them to the levels induced by poly I:C. We also determined the effects that the two viruses and poly I:C provoked on the levels of expression of these chemokines in vitro in head kidney leucocytes. Overall, VHSV was capable of modulating gammaIP, CXCd, CK1, CK3, CK5B, CK6 and CK12, while IPNV induced a very different chemokine profile and affected CK1, CK5B, CK6, CK7A, CK9 and CK12. On the other hand, a viral mimic such as poly I:C was capable of up-regulating gammaIP, CXCd, CK1, CK3, CK5B, CK7A and CK12. As more information becomes available concerning the immune role and target cells that these chemokines have on rainbow trout, we would be able to better interpret the importance of these differences in the pathogenicity of these two viruses.

Immune effects observed after the injection of plasmids coding for rainbow trout (Oncorhynchus mykiss) CK5B, CK6 and CK7A chemokines demonstrate their immunomodulatory capacity and reveal CK6 as a major interferon inducer

In the current study, we have determined the immune effects of the intramuscular injection of eukaryotic expression plasmids coding for rainbow trout (Oncorhynchus mykiss) CK5B, CK6 or CK7A CC chemokines (pCK5B, pCK6 and pCK7A) as a first step towards the establishment of their biological role. We have studied the levels of expression of several immune genes in the spleen and head kidney by real-time PCR in comparison to the levels observed in animals injected with the empty plasmid. Concerning the levels of expression of these CC chemokines and the CXC chemokine, interleukin 8 (IL-8), each plasmid induced up-regulation on expression levels of its coded chemokine in the head kidney and spleen, but also affected the expression of other chemokines. Both pCK6 and pCK7A induced the expression of the other two CC chemokines, while pCK5B induced CK7A but not CK6. Both pCK5B and pCK7A induced IL-8 as well. pCK6 was the only plasmid that induced IL-1beta in the head kidney, whereas in the spleen, this occurred only with pCK5B. Different effects on the head kidney and spleen were also visible for tumour necrosis factor alpha (TNF-alpha), since the three plasmids induced this cytokine in the head kidney, but only pCK5B and pCK6 in the spleen. Concerning the effects on type I interferon (IFN), again pCK6 induced the strongest enhancement in the head kidney, while in the spleen it was pCK5B. However, the levels of expression of the Mx gene, know to be induced by type I IFN correlated with the CK6-induced IFN levels in the head kidney, but not with the CK5B-induced IFN in head kidney or spleen, suggesting an inhibition of Mx mRNA levels independent of IFN due to CK5B. The clear effect of pCK6 on the levels of expression of IFN-gamma and its strong effects on type I IFN, in contrast with its recent adscription to the CCL17/22 group linked to Th2 responses, were verified by studying the in vitro effects of recombinant CK6 on head kidney leukocytes. Again in this case, recombinant CK6 strongly induced type I IFN, Mx and IFN-gamma to a lesser extent, revealing CK6 as a potent IFN inducer in contrast to its mammalian homologues. Finally, effects on major histocompatibility complex (MHC)-IIalpha, CD4 and CD8alpha expression demonstrate that the three chemokines are able to mobilize antigen-presenting cells, CD4(+) and CD8(+) lymphocytes.

In vitro and in vivo immune responses induced by a DNA vaccine encoding the VP2 gene of the infectious pancreatic necrosis virus

The work presented here describes the construction of a plasmid encoding the VP2 gene of the infectious pancreatic necrosis virus (IPNV), its expression in BF-2 cells and an evaluation of its activity in brown trout (Salmo trutta L) soon after injection. Preliminary experiments to evaluate the potential of the plasmid to induce neutralizing antibodies were also performed. We established a BF-2 cell line that expresses VP2 constitutively and we examined the infection of these VP2-transfected BF-2 cells with homologous and heterologous viruses. The expression kinetics of IFN, and of the IFN-induced genes Mx and ISG15, was also evaluated in brown trout over a 15 day interval, and quantified by real-time or semi-quantitative PCR. Type I IFN and Mx are markers of the non-specific innate immune response to viruses and they are involved in antiviral defences. Our results demonstrate that expression of the IPNV VP2 protein in BF-2 cells induces an antiviral state against IPNV and against the infectious haematopoietic necrosis virus (IHNV). In BF-2 infected cells, VP2 inhibited both the IPNV and IHNV-induced cytopathic effect to some extent, as well as the virus yield. In vivo, VP2 was expressed in haematopoietic tissues such as the head kidney of 7 month-old trout. In addition, it induced early immune responses and specific immunity 30 days after injection. IFN mRNA expression increased sharply on the 1st and 15th day post-injection and expression of other IFN-induced genes as Mx and ISG15 was also detected soon after vaccination of brown trout. Moreover, specific antibodies were detected 30 days after vaccination. These results suggest that the VP2 gene is a good candidate for the design of IPNV-DNA vaccines and to investigate the use of cytokines as co-stimulatory molecules.

Molecular characterization and expression profiles in response to bacterial infection of Chinese soft-shelled turtle interleukin-8 (IL-8), the first reptilian chemokine gene

In this study, an IL-8 homologue has been cloned and identified from a reptile, Chinese soft-shelled turtle for the first time. The full-length cDNA of turtle IL-8 was 1188bp and contained a 312bp open reading frame (ORF) coding for a protein of 104 amino acids. The chemokine CXC domain, which contained Glu-Leu-Arg (ELR) motif and four cysteine residues, was well conserved in turtle IL-8. The 4924bp genomic DNA of turtle IL-8 contained four exons and three introns. Phylogenetic analysis showed that the amino acid sequence of turtle IL-8 clustered together with birds. RT-PCR analysis showed that turtle IL-8 mRNA was constitutively expressed liver, spleen, kidney, heart, blood and intestine tissues of control turtles. Real-time quantitative PCR analysis further indicated that the turtle IL-8 mRNA expression was apparent in various tissues at 8h and up-regulated significantly during 8h-7d after Aeromonas hydrophila infection. The present studies will help us to understand the evolution of IL-8 molecule and the inflammatory response mechanism in reptiles.

Animal models for target diseases in gene therapy--using DNA and siRNA delivery strategies

Nanoparticles, including lipopolyamines leading to lipoplexes, liposomes, and polyplexes are targeted drug carrier systems in the current search for a successful delivery system for polynucleic acids. This review is focused on the impact of gene and siRNA delivery for studies of efficacy, pharmacodynamics, and pharmacokinetics within the setting of the wide variety of in vivo animal models now used. This critical appraisal of the recent literature sets out the different models that are currently being investigated to bridge from studies in cell lines through towards clinical reality. Whilst many scientists will be familiar with rodent (murine, fecine, cricetine, and musteline) models, few probably think of fish as a clinically relevant animal model, but zebrafish, madake, and rainbow trout are all being used. Larger animal models include rabbit, cat, dog, and cow. Pig is used both for the prevention of foot-and-mouth disease and human diseases, sheep is a model for corneal transplantation, and the horse naturally develops arthritis. Non-human primate models (macaque, common marmoset, owl monkey) are used for preclinical gene vector safety and efficacy trials to bridge the gap prior to clinical studies. We aim for the safe development of clinically effective delivery systems for DNA and RNAi technologies.

Will advances in fish immunology change vaccination strategies?

This review will discuss some of the recent advances in discovering immune genes in fish, in terms of their relevance to vaccine design and development. Particular emphasis will be placed on the many cytokine and costimulatory molecules now known, with examples drawn from the mammalian literature as to their potential value for fish vaccinology. A new area of vaccine research will also be touched upon, where efficacious responses are elicited by inhibiting the natural negative regulators of immune responses, such as Treg cell products and SOCS proteins.

NK-like and oxidative burst activities are the main early cellular innate immune responses activated after virus inoculation in reservoir fish

Viral diseases are a major problem in fish farming and a deeper knowledge of the immunological mechanisms playing a part in the antiviral defence is still important. Moreover, fish farming practices (high densities, new areas of culture and egg/larvae/adult transport) are significantly increasing the spread of viruses and the number of susceptible or reservoir fish species. In this last point, no studies have focused on the immunological mechanisms playing a part in the antiviral responses in reservoir and non-susceptible fish species. Thus, we have evaluated the very early innate immune responses of gilthead seabream (Sparus aurata) to the virus causing viral haemorrhagic septicaemia (VHSV) in salmonids since this virus has been found in seabream and neighbouring farmed marine fish species acting as a viral reservoir. The virus was detected in liver, head-kidney, spleen and peritoneal cavity suggesting that the virus reached these tissues but did not replicate as viral expression was almost absent by 72 h post-inoculation. Interestingly, VHSV provoked an influx of leucocytes to the peritoneal cavity and a redistribution of peritoneal exudate (PELs) and head-kidney (HKLs) leucocytes and their innate immune responses (non-specific cytotoxic (NCC or NK-like) activity, phagocytosis, reactive oxygen intermediate (ROI) production and myeloperoxidase (MPO) activity) were generally increased demonstrating that the immune system is activated and involved in the clearance of the virus. Strikingly, NK-like, ROI and MPO were the most enhanced by the presence of VHSV in both PELs and HKLs suggesting that these early innate immune events are crucial during early viral infection stages in non-susceptible or reservoir species. Differences in the immunological mechanisms between susceptible and reservoir species and with other particulate antigens are discussed.

Teleostean IL11b exhibits complementing function to IL11a and expansive involvement in antibacterial and antiviral responses

Interleukin 11 is a class-1 helical cytokine, having the four-helix bundle structure, possessing pleiotropic characteristics involved in physiological processes including blood production, bone formation and placentation. The interleukin 11 paralogues (IL11a and IL11b) have been identified in fish with only IL11a from carp and trout have been characterized and analyzed for its expression thus far. Here, we cloned and studied the structure and expression of IL11b in Japanese flounder (Paralichthys olivaceus), and compared this with the existing information on fish IL11 paralogues. Japanese flounder IL11b (poIL11b) cDNA is composed of 1536 bp encoding for 201 aa residues with a 23 aa leader peptide, three cysteine residues (C12, C183 and C198) and four potential N-linked glycosylation sites. poIL11b does not show constitutive expression in tissues of adult fish except for the very slight expression in kidney and spleen, and the very high expression in peripheral blood leukocytes (PBLs). poIL11b is transiently up-regulated by bacterial lipopolysaccharide (LPS) and increasingly stimulated by the IFN inducer poly I:C in kidney, spleen and peripheral blood leukocytes of adult fish in vitro. It is likewise slightly stimulated by Edwardsiella tarda infection but is highly expressed after hirame rhabdovirus (HIRRV) infection in kidney of juvenile fish. The stimulation studies suggest that poIL11b, aside from its role in bacterial infection, is well involved in antiviral responses. Moreover, poIL11b structure and expression pattern appears to be slightly distinct and opposite to IL11a, respectively, suggesting a complementation of function of the duplicate fish IL11 genes.

Interleukin 8 and CK-6 chemokines specifically attract rainbow trout (Oncorhynchus mykiss) RTS11 monocyte-macrophage cells and have variable effects on their immune functions

In the current work, we have demonstrated that both rainbow trout (Oncorhynchus mykiss) interleukin 8 (IL-8), a CXC chemokine, and CK-6, a CC chemokine, are able of efficiently attracting RTS11, a rainbow trout established macrophage-monocyte-like cell line. Interestingly, two sub-populations of non-adherent cells are distinguishable by flow cytometry that could be identified as immature monocyte- and mature macrophage-like populations, respectively, and the two chemokines studied exert their effects on different populations. Although IL-8 specifically attracts the monocyte-like sub-population, CK-6 specifically attracts the macrophage-like cell sub-population. We have also determined the effects of both of these chemokines on RTS11 phagocytosis, respiratory burst and the expression of other immune-related genes. We found that IL-8 inhibited the phagocytosis capacity of RTS11 cells belonging to the macrophage-like profile. No effect was observed, however, on the respiratory burst, immune function that has been considerably affected throughout the establishment of the cell culture. Concerning the effect that IL-8 and CK-6 have on the expression of other immune genes, we found that IL-8 significantly induced the levels of expression of CK-6, IL-8, pro-inflammatory cytokines such as IL-1beta and tumour necrosis factor alpha (TNF-alpha) of RTS11 cells. On the other hand, CK-6 induced the levels of expression of IL-8, iNOS and the integrin CD-18, while it had very faint effect on pro-inflammatory cytokines. These results constitute one of the very few studies in which the effect of IL-8, a CXC chemokine, on monocyte-like cells is described. Moreover, it demonstrates that different monocyte-macrophage sub-populations have different reactivity to different chemokines.

Innate immunomodulation with recombinant interferon-alpha enhances resistance of rainbow trout (Oncorhynchus mykiss) to infectious hematopoietic necrosis virus

We examined the in vivo immunostimulatory effects of a recombinant Atlantic salmon (Salmo salar) interferon-alpha2 (rSasaIFN-alpha2). The mature rSasaIFN-alpha2, expressed and purified from Escherichia coli, was administered to rainbow trout (Oncorhynchus mykiss) via the oral, immersion, or intraperitoneal (IP) injection route. Injection of rSasaIFN-alpha2 at 0.1microg/g fish gave significantly greater protection than a phosphate buffered saline (PBS) injection against a lethal challenge of infectious hematopoietic necrosis virus (IHNV), with a relative percent survival of 39%. Relative percent survival (RPS) increased significantly to 92% when the fish were injected with rSasaIFN-alpha2 at 1microg/g fish. Antiviral protection was evident for up to 7 days post-injection of rSasaIFN-alpha2. Administration of rSasaIFN-alpha2 by the oral or immersion route was not protective, and the fish succumbed to virus infection. The level of systemic IFN-induced expression of the Mx1 gene was significantly greater (p<0.01) in the IFN-injected group than in the PBS-injected group, and this was correlated with the fish survival rates in the challenge study. We used relative quantitative real-time polymerase chain reactions to examine the systemic expression of several other IFN-induced genes (including genes for IFN1, IFN regulatory factors 1 and 2, MHC-I, STAT1, vig-1, and GBP) and found that their expression was significantly increased 1-day post-rSasaIFN-alpha2 injection. Expression of the IFN-gamma and interleukin-1beta genes was not significantly increased. Thus, a salmonid rIFN-alpha can modulate the innate immune response of rainbow trout and mediate early antiviral protection against IHNV.

Comparative analysis of the acute response of the trout, O. mykiss, head kidney to in vivo challenge with virulent and attenuated infectious hematopoietic necrosis virus and LPS-induced inflammation

BACKGROUND

The response of the trout, O. mykiss, head kidney to bacterial lipopolysaccharide (LPS) or active and attenuated infectious hematopoietic necrosis virus (IHNV and attINHV respectively) intraperitoneal challenge, 24 and 72 hours post-injection, was investigated using a salmonid-specific cDNA microarray.

RESULTS

The head kidney response to i.p. LPS-induced inflammation in the first instance displays an initial stress reaction involving suppression of major cellular processes, including immune function, followed by a proliferative hematopoietic-type/biogenesis response 3 days after administration. The viral response at the early stage of infection highlights a suppression of hematopoietic and protein biosynthetic function and a stimulation of immune response. In fish infected with IHNV a loss of cellular function including signal transduction, cell cycle and transcriptional activity 72 hours after infection reflects the tissue-specific pathology of IHNV infection. attIHNV treatment on the other hand shows a similar pattern to native IHNV infection at 24 hours however at 72 hours a divergence from the viral response is seen and replace with a recovery response more similar to that observed for LPS is observed.

CONCLUSION

In conclusion we have been able to identify and characterise by transcriptomic analysis two different types of responses to two distinct immune agents, a virus, IHNV and a bacterial cell wall component, LPS and a 'mixed' response to an attenuated IHNV. This type of analysis will lead to a greater understanding of the physiological response and the development of effective immune responses in salmonid fish to different pathogenic and pro-inflammatory agents.

Bath vaccination of rainbow trout (Oncorhynchus mykiss Walbaum) against Yersinia ruckeri: effects of temperature on protection and gene expression

Protection of rainbow trout fry following bath vaccination with a bacterin of Y. ruckeri O1, the bacterial pathogen causing enteric red mouth disease (ERM), was investigated at 5, 15 and 25 degrees C. Rainbow trout fry were acclimatised for 8 weeks at the three temperatures before vaccination. They were subsequently challenged with Y. ruckeri 4 and 8 weeks post-vaccination which demonstrated a significant protection of vaccinated fish kept at 15 degrees C. No protective effect of vaccination in rainbow trout reared at 5 and 25 degrees C could be recorded. Spleen tissue was sampled from vaccinated and control fish at 0, 8, 24 and 72 h post-vaccination in order to analyse gene transcript profiles using quantitative real-time RT-PCR (q-PCR). Gene expression in fish vaccinated at 15 degrees C (the protected fish) was up-regulated with regard to the pro-inflammatory cytokines IFN-gamma, TNF-alpha, IL-6 and the anti-inflammatory cytokines IL-10 and TGF-beta, the cell receptors TcR, CD8alpha, CD4, C5aR and the teleost specific immunoglobulin IgT. Passive immunisation using transfer of plasma from vaccinated fish to naïve fish conferred no protection. This indicates that humoral factors such as Ig and complement are less important in the protection induced by bath vaccination. Expression of cellular factors such as CD8alpha was significantly increased in the protected trout and this suggests that cellular factors including cytotoxic T-cells could play a role in immunity against Y. ruckeri.