Identification of novel rainbow trout (Onchorynchus mykiss) chemokines, CXCd1 and CXCd2: mRNA expression after Yersinia ruckeri vaccination and challenge

Innate and adaptive immune response of Rainbow trout (Oncorhynchus mykiss) naturally infected with Yersinia ruckeri

Rainbow trout is an important fish species for Peruvian artisanal aquaculture, comprising over 60 % of the total aquaculture production. However, their industry has been highly affected by several bacterial agents such as Yersinia ruckeri. This pathogen is the causative agent of Enteric Redmouth Disease, and causes high mortality in fingerlings and chronic infection in adult rainbow trout. To date, the immune response of rainbow trout against Y. ruckeri has been well studied in laboratory-controlled infection studies (i.e. intraperitoneal infection, bath immersion), however, the immune response during natural infection has not been explored. To address this, in this study, 35 clinically healthy O. mykiss without evidence of lesions or changes in behavior and 32 rainbow trout naturally infected by Y. ruckeri, were collected from semi-intensive fish farms located in the Central Highlands of Peru. To evaluate the effect on the immune response, RT-qPCR, western blotting, and ELISA were conducted using head kidney, spleen, and skin tissues to evaluate the relative gene expression and protein levels. Our results show a significant increase in the expression of the pro-inflammatory cytokines il1b, tnfa, and il6, as well as ifng in all three tissues, as well as increases in IL-1β and IFN-γ protein levels. The endogenous pathway of antigen presentation showed to play a key role in defense against Y. ruckeri, due to the upregulation of mhc-I, tapasin, and b2m transcripts, and the significant increase of Tapasin protein levels in infected rainbow trout. None of the genes associated with the exogenous pathway of antigen presentation showed a significant increase in infected fish, suggesting that this pathway is not involved in the response against this intracellular pathogen. Finally, the transcripts of immunoglobulins IgM and IgT did not show a modulation, nor were the protein levels evaluated in this study.

IL8 of Takifugu rubripes is a chemokine that interacts with peripheral blood leukocytes and promotes antibacterial defense

Interleukin 8 (IL8) is a CXC chemokine that plays a crucial role on promoting inflammatory response and immune regulation. In teleost, IL8 can induce the migration and activation of immune cells. However, the biological functions of IL8 are still unknown in Takifugu rubripes. In this study, we examined the biological characteristics of TrIL8 in T. rubripes. TrIL8 is composed of 98 residues and contained a chemokine CXC domain. We found that the TrIL8 expression was detected in diverse organs and significantly increased by Vibrio harveyi or Edwardsiella tarda challenge. The recombinant TrIL8 (rTrIL8) exhibited significantly the binding capacities to 8 tested bacteria. In addition, rTrIL8 could bind to peripheral blood leukocytes (PBL), and increased the expression of immune gene, resistance to bacterial infection, respiratory burst, acid phosphatase activity, chemotactic activity, and phagocytic activity of PBL. In the presence of rTrIL8, T. rubripes was enhanced the resistance to V. harveyi infection. These results indicated that TrIL8 is a chemokine and involved in the activation of immune cells against bacterial infection in teleost.

CC and CXC chemokines in turbot (Scophthalmus maximus L.): Identification, evolutionary analyses, and expression profiling after Aeromonas salmonicida infection

Chemokines are a superfamily of structurally related cytokines, which exert essential roles in guiding cell migration in development, homeostasis, and immunity. CC and CXC chemokines are the two major subfamilies in teleost species. In this study, a total of seventeen CC and CXC chemokines, with inclusion of twelve CC and five CXC chemokines, were systematically identified from the turbot genome, making turbot the teleost harboring the least number of CC and CXC chemokines among all teleost species ever reported. Phylogeny, synteny, and genomic organization analyses were performed to annotate these genes, and multiple chemokine genes were identified in the turbot genome, due to the tandem duplications (CCL19 and CCL20), the whole genome duplications (CCL20, CCL25, and CXCL12), and the teleost-specific members (CCL34-36, CCL44, and CXCL18). In addition, chemokines were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in liver, gill, and spleen. Moreover, most chemokines were significantly differentially expressed in gill and spleen after Aeromonas salmonicida infection, and exhibited tissue-specific and time-dependent manner. Finally, protein-protein interaction network (PPI) analysis indicated that turbot chemokines interacted with a few immune-related genes such as interleukins, cathepsins, stats, and TLRs. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokines in teleost.

Functional and Molecular Immune Response of Rainbow Trout (Oncorhynchus mykiss) Following Challenge with Yersinia ruckeri

Currently, aquaculture production of rainbow trout (Oncorhynchus mykiss) is a multibillion dollar industry; nevertheless, the development of this sector has not been exempt from pitfalls related to the recurrent presence of pathogens of bacterial origin. This is the case of Yersinia ruckeri, the etiologic agent of the infectious pathology known as Enteric Red Mouth Disease (ERM), causing serious economic losses that can be as high as 30–70% of production. Although several studies have been performed regarding pathogen features and virulence factors, more information is needed about the host defense mechanism activation after infection. Given this perspective, this study aimed to evaluate rainbow trout’s short-term innate immune response against infection with Y. ruckeri. A series of factors linked to the innate immune response were evaluated, including determination of hematological parameters, oxidative stress biomarkers, and analysis of the expression of immune-related genes. Results showed a significant decrease in several hematological parameters (white blood cell count, hematocrit, neutrophils, monocytes, lymphocytes, and thrombocytes) and oxidative stress indicators (SOD) between the control and infected groups. In addition, there were significant differences in the level of gene expression between infected individuals and the control group. Most of these genes (il-1β, il-8, il-10, tnf-α1, tnf-α2, socs3, mmp-9, cath, hsp-70, saa, fer, pcb) were upregulated within the first 24 h following infection. Results from this study showed more insights into the short-term immune response of rainbow trout to infection with Y. ruckeri, which may be useful for the establishment of biomarkers that may be used for the early detection of ERM.

CXC chemokines and their receptors in black rockfish (Sebastes schlegelii): Characterization, evolution analyses, and expression pattern after Aeromonas salmonicida infection

Chemokines are crucial regulators of cell mobilization for development, homeostasis, and immunity. Chemokines signal through binding to chemokine receptors, a superfamily of seven-transmembrane domain G-coupled receptors. In the present study, seventeen CXC chemokine ligands (SsCXCLs) and nine CXC chemokine receptors (SsCXCRs) were systematically identified from Sebastes schlegelii genome. Phylogeny, synteny, and evolutionary analyses were performed to annotate these genes, indicating that the tandem duplications (CXCL8, CXCL11, CXCL32, CXCR2, and CXCR3), the whole genome duplications (CXCL8, CXCL12, CXCL18, and CXCR4), and the teleost-specific members (CXCL18, CXCL19, and CXCL32) led to the expansion of SsCXCLs and SsCXCRs. In addition, SsCXCLs and SsCXCRs were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in head kidney, liver, gill and spleen. Moreover, most SsCXCLs and SsCXCRs were significantly differentially expressed in head kidney, liver, and gill after Aeromonas salmonicida infection, and exhibited tissue-specific and time-dependent manner. Finally, protein-protein interaction network (PPI) analysis indicated that SsCXCLs and SsCXCRs interacted with a few immune-related genes such as interleukins, cathepsins, CD genes, and TLRs, etc. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokines and receptors in teleost.

Transcriptome profiling of immune response to Yersinia ruckeri in spleen of rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Yersinia ruckeri is a pathogen that can cause enteric redmouth disease in salmonid species, damaging global production of economically important fish including rainbow trout (Oncorhynchus mykiss). Herein, we conducted the transcriptomic profiling of spleen samples from rainbow trout at 24 h post-Y. ruckeri infection via RNA-seq in an effort to more fully understand their immunological responses.

RESULTS

We identified 2498 differentially expressed genes (DEGs), of which 2083 and 415 were up- and down-regulated, respectively. We then conducted a more in-depth assessment of 78 DEGs associated with the immune system including CCR9, CXCL11, IL-1β, CARD9, IFN, TNF, CASP8, NF-κB, NOD1, TLR8α2, HSP90, and MAPK11, revealing these genes to be associated with 20 different immunological KEGG pathways including the Cytokine-cytokine receptor interaction, Toll-like receptor signaling, RIG-I-like receptor signaling, NOD-like receptor signaling, and MAPK signaling pathways. Additionally, the differential expression of 8 of these DEGs was validated by a qRT-PCR approach and their immunological importance was then discussed.

CONCLUSIONS

Our findings provide preliminary insight on molecular mechanism underlying the immune responses of rainbow trout following Y. ruckeri infection and the base for future studies of host-pathogen interactions in rainbow trout.

Molecular characterization of a new fish specific chemokine CXCL_F6 in large yellow croaker (Larimichthys crocea) and its role in inflammatory response

Chemokines are a superfamily of structurally related chemotactic cytokines exerting significant roles in regulating cell migration and activation. Currently, five subgroups of fish specific CXC chemokines, named CXCL_F1-CXCL_F5, have been identified in teleost fish. However, understanding of the functions of these fish specific CXC chemokines is still limited. Here, a new member of fish specific CXC chemokines, LcCXCL_F6, was cloned from large yellow croaker Larimichthys crocea. Its open reading frame (ORF) is 369 nucleotides long, encoding a peptide of 122 amino acids (aa). The deduced LcCXCL_F6 protein contains a 19-aa signal peptide and a 103-aa mature polypeptide, which has four conserved cysteine residues (C²⁸, C³⁰, C⁵⁶, and C⁷²), as found in other known CXC chemokines. Phylogenetic analysis showed LcCXCL_F6 formed a separate clade with sequences from other fish species, tentatively named CXCL_F6, distinct from the clades formed by fish CXCL_F1-5 and mammalian CXC chemokines. The LcCXCL_F6 transcripts were constitutively expressed in all examined tissues and significantly up-regulated in the spleen and head kidney tissues by poly (I:C) and Vibrio alginolyticus. Its transcripts were also detected in primary head kidney leukocytes (HKLs), peripheral blood leucocytes (PBLs), and large yellow croaker head kidney (LYCK) cell line, and significantly up-regulated by poly(I:C), lipopolysaccharide (LPS), and peptidoglycan (PGN) in HKLs. Recombinant LcCXCL_F6 protein (rLcCXCL_F6) could not only chemotactically attract monocytes/macrophages and lymphocytes from PBLs, but also enhance NO release and expression of proinflammatory cytokines (TNF-α, IL-1β, and CXCL8) in monocytes/macrophages. These results indicate that LcCXCL_F6 plays a role in mediating the inflammatory response.

The CXC chemokines and CXC chemokine receptors in orange-spotted grouper (Epinephelus coioides) and their expression after Singapore grouper iridovirus infection

Chemokines comprise a group of small molecular weight (6-14 kDa) cytokines; chemokine receptors are a superfamily of seven transmembrane domain G-coupled receptors. Both chemokines and their receptors have important roles in immune surveillance, inflammation, and development. Recently, 9 CXC chemokine ligands (CXCLs) and 8 CXC chemokine receptors (CXCRs) were identified and cloned from orange-spotted grouper (Epinephelus coioides) and annotated by phylogenetic and syntenic analyses. We detected mRNA transcripts for CXCLs and CXCRs in healthy tissues of E. coioides. Our data show that CXCL genes are highly expressed in the spleen, kidney and liver and that CXCR genes are ubiquitously expressed, rather than being expressed only in immune organs. Analysis of gene expression after Singapore grouper iridovirus infection indicated that CXCL and CXCR genes are regulated in a gene-specific manner. CXCL8 and CXCL12a were significantly upregulated in the spleen, kidney and liver of resistant fish, indicating potential roles in immunity against the pathogen. Additionally, CXCR4a was upregulated in all three organs in resistant fish, suggesting that CXCL8 or CXCL12a may participate in the immune response via interaction with CXCR4a. In addition, the new orange-spotted grouper receptor CXCR1b was found to be upregulated in the spleen and kidney of resistant fish, indicating that this receptor plays an important role in immune responses to viral infection. These results are valuable for comparative immunological studies and provide insight into the roles of these genes in viral infection.

The chemokinome superfamily: II. The 64 CC chemokines in channel catfish and their involvement in disease and hypoxia responses

Chemokines are a superfamily of structurally related chemotactic cytokines exerting significant roles in regulating cell migration and activation. Based on the arrangement of the first four cysteine residues, they are classified into CC, CXC, C and CX3C subfamilies. In this study, a complete set of 64 CC chemokine ligand (CCL) genes was systematically identified, annotated, and characterized from the channel catfish genome. Extensive phylogenetic and comparative genomic analyses supported their annotations, allowing establishment of their orthologies, revealing fish-specific CC chemokines and the expansion of CC chemokines in the teleost genomes through lineage-specific tandem duplications. With 64 genes, the channel catfish genome harbors the largest numbers of CC chemokines among all the genomes characterized to date, however, they fall into 11 distinct CC chemokine groups. Analysis of gene expression after bacterial infections indicated that the CC chemokines were regulated in a gene-specific and time-dependent manner. While only one member of CCL19 (CCL19a.1) was significantly up-regulated after Edwardsiella ictaluri infection, all CCL19 members (CCL19a.1, CCL19a.2 and CCL19b) were significantly induced after Flavobacterium columnare infection. In addition, CCL19a.1, CCL19a.2 and CCL19b were also drastically up-regulated in ESC-susceptible fish, but not in resistant fish, suggesting potential significant roles of CCL19 in catfish immune responses. High expression levels of certain CC appeared to be correlated with susceptibility to diseases and intolerance to hypoxia.

A CXCL ortholog from Hippocampus abdominalis: Molecular features and functional delineation as a pro-inflammatory chemokine

Chemokines are a family of chemotactic cytokines that regulate leukocyte migration. They are classified into four groups namely, CXC, CC, C and CX₃C, based on the formation of a disulfide bridge. Among these, CXC chemokines have been identified as the largest group of chemokines in humans. In this study, we identified and functionally characterized a homolog of CXC chemokine from the big-belly seahorse, Hippocampus abdominalis, and designated it as ShCXCL. The cDNA of ShCXCL composed of a 342-bp open reading frame encoding 113 amino acids (aa). The CXC family-specific small cytokine domain (SCY) was identified from the mature peptide region, which comprised of a conserved CXC motif. As ShCXCL lacks an ELR (Glutamic acid-Leucine-Arginine) motif, it belongs to ELR^- subfamily. The recombinant ShCXCL protein strongly induced the nitric oxide (NO) production in macrophage cells (RAW 264.7 cell line) and showed the chemotactic effect on flounder peripheral blood leukocytes. Tissue profiling showed a ubiquitous expression pattern in all examined tissues, with a high abundance in spleen. The up-regulated mRNA expression pattern of ShCXCL was observed in blood and kidney tissues after immune stimulation by live bacteria, such as Streptococcus iniae and Edwardsiella tarda, and mitogens, such as lipopolysaccharides (LPS) and polyinosinic:polycytidylic acid (poly I:C), suggesting its important role in host immune defense against microbial infection.

Characterization of basic immune function parameters in the fathead minnow (Pimephales promelas), a common model in environmental toxicity testing

The fathead minnow (Pimephales promelas) is an environmental sentinel species, commonly used in toxicity testing. However, there is a lack of data regarding basic immune function in this species. To improve the usefulness of the fathead minnow as a model for basic immune function and immunotoxicity, this study sought to 1) compare the differential expression of immune function genes in naïve fathead minnows and 2) determine the effects of pathogen exposure on immune gene expression and spleen index. To accomplish this, kidney, spleen and liver tissue were collected three days post injection (dpi) from adult male fathead minnows from each of the following groups: 1) uninjected control 2) sham-injected (Hank's balanced salt solution) and 3) pathogen-injected (Yersinia ruckeri). Spleen tissue was also collected at seven and 14 dpi. Differential tissue expression of immune function genes was evaluated in naïve minnows and expression patterns were similar to those found in other fish species, with liver tissue generally having the highest amount of expression. Following pathogen injection, the expression of complement component 3 (c3) (4.4-fold, kidney; 2.5-fold, liver), interleukin 11 (il11) (4.8-fold, kidney; 15.2-fold, liver) and interleukin 1β (il1β) (8.2-fold, kidney; 17.2-fold, spleen; 2.6-fold, liver) were significantly upregulated. Elastase 2 (elas2) was significantly downregulated (5.8-fold) in liver tissue. A significant increase in spleen index at seven dpi was also observed in pathogen-injected minnows. This study has identified endpoints that are part of the normal response to pathogen in fathead minnows, an essential step toward the development of the fathead minnow as a model for immunotoxicity evaluations.

The chemokinome superfamily in channel catfish: I. CXC subfamily and their involvement in disease defense and hypoxia responses

Chemokines are a superfamily of structurally related chemotactic cytokines exerting significant roles in regulating cell migration and activation. They are defined by the presence of four conserved cysteine residues and are divided into four subfamilies depending on the arrangement of the first two conserved cysteines residues: CXC, CC, C and CX3C. In this study, a complete set of 17 CXC chemokine ligand (CXCL) genes was systematically identified and characterized from channel catfish genome through data mining of existing genomic resources. Phylogenetic analysis allowed annotation of the 17 CXC chemokines. Extensive comparative genomic analyses supported their annotations and orthologies, revealing the existence of fish-specific CXC chemokines and the expansion of CXC chemokines in the teleost genomes. The analysis of gene expression after bacterial infection indicated the CXC chemokines were expressed in a gene-specific manner. CXCL11.3 and CXCL20.3 were expressed significantly higher in resistant fish than in susceptible fish after ESC infection, while CXCL20.2 were expressed significantly higher in resistant fish than in susceptible fish after columnaris infection. The expression of those CXC chemokines, therefore can be a useful indicator of disease resistance. A similar pattern of expression was observed between resistant and susceptible fish with biotic and abiotic stresses, ESC, columnaris and hypoxia, suggesting that high levels of expression of the majority of CXC chemokines, with exception of CXC11 and CXC20, are detrimental to the host.

Identification of a fish specific chemokine CXCL_F2 in large yellow croaker (Larimichthys crocea) reveals its primitive chemotactic function

Chemokines are a superfamily of cytokines regulating immune cell migration under both inflammatory and normal physiological conditions. Currently, a number of fish specific CXC chemokines, named as CXCL_F1-5, have been identified in several species. However, understanding of their functional characteristics is still limited. In this study, we identified a fish specific chemokine CXCL_F2 (LycCXCL_F2) from large yellow croaker (Larimichthys crocea). The open reading frame (ORF) of LycCXCL_F2 is 348 nucleotides long, encoding a protein of 115 amino acids (aa). The deduced LycCXCL_F2 protein contains a 20-aa signal peptide and a 95-aa mature polypeptide. Phylogenetic analysis showed that LycCXCL_F2 fell into a major clade formed by CXCL_F2 sequences and was separated from CXCL_F1 and CXCL_F3-5 subgroups. LycCXCL_F2 mRNA transcript was constitutively expressed in various tissues, with the highest levels in spleen and head kidney. After stimulation with inactivated trivalent bacterial vaccines, LycCXCL_F2 mRNA transcription was significantly increased in both spleen and head kidney. Moreover, recombinant LycCXCL_F2 protein exhibited obvious chemotaxis to monocytes, lymphocytes and eosnophils of PBLs isolated from large yellow croaker, but could not induce the respiratory burst of macrophages. These results indicate that this fish specific CXC chemokine LycCXCL_F2 possesses primitive chemotactic activity and may play a role in immune response in large yellow croaker.

Comparative study of CXC chemokines modulation in brown trout (Salmo trutta) following infection with a bacterial or viral pathogen

Chemokine modulation in response to pathogens still needs to be fully characterised in fish, in view of the recently described novel chemokines present. This paper reports the first comparative study of CXC chemokine genes transcription in salmonids (brown trout), with a particular focus on the fish specific CXC chemokines (CXCL_F). Adopting new primer sets, optimised to specifically target mRNA, a RT-qPCR gene screening was carried out. Constitutive gene expression was assessed first in six tissues from SPF brown trout. Transcription modulation was next investigated in kidney and spleen during septicaemic infection induced by a RNA virus (Viral Haemorrhagic Septicaemia virus, genotype Ia) or by a Gram negative bacterium (Yersinia ruckeri, ser. O1/biot. 2). From each target organ specific pathogen burden, measured detecting VHSV-glycoprotein or Y. ruckeri 16S rRNA, and IFN-γ gene expression were analysed for their correlation to chemokine transcription. Both pathogens modulated CXC chemokine gene transcript levels, with marked up-regulation seen in some cases, and with both temporal and tissue specific effects apparent. For example, Y. ruckeri strongly induced chemokine transcription in spleen within 24h, whilst VHS generally induced the largest increases at 3d.p.i. in both tissues. This study gives clues to the role of the novel CXC chemokines, in comparison to the other known CXC chemokines in salmonids.

Yersinia ruckeri lipopolysaccharide is necessary and sufficient for eliciting a protective immune response in rainbow trout (Oncorhynchus mykiss, Walbaum)

Enteric redmouth disease (ERM), caused by Yersinia ruckeri, has been controlled successfully using immersion-applied bacterin vaccines for several decades. While the host response to vaccination and the mechanism of protection of this vaccine have been elucidated, the bacterial components eliciting protection have remained unclear. Here we show that highly purified serotype O1 Y. ruckeri lipopolysaccharide (LPS) is sufficient to induce a protective response to experimental challenge in rainbow trout (Oncorhynchus mykiss). Dose response experiments demonstrated that Y. ruckeri LPS at doses of 1 ng/fish and above resulted in essentially complete protection and doses as low as 0.01 ng/fish (1.38 ng/kg) resulted in significant protection, thus demonstrating the extremely high potency of this immunogen. Analysis of the Y. ruckeri genome identified a cluster of putative O-antigen biosynthetic genes specific to serotype O1 strains. This cluster primarily consisted of genes encoding proteins predicted to function in the biosynthesis of legionamic acid, a nonulosonic acid known to be part of the O-polysaccharide repeat of O1 Y. ruckeri. Mutation of the nab2 gene, a nonulosonic acid biosynthesis gene (nab gene), resulted in production of severely truncated forms of LPS. Vaccination with bacterin vaccines derived from the nab2 mutant and its wild type parent strain demonstrated that LPS is a required component of the whole-cell bacterin vaccine and suggests that LPS is the only cellular component contributing to the protective response elicited by this vaccine. We speculate that the exceptionally high potency of Y. ruckeri LPS accounts for the unusual success of this vaccine when delivered by immersion.

Teleost Chemokines and Their Receptors

Chemokines are a superfamily of cytokines that appeared about 650 million years ago, at the emergence of vertebrates, and are responsible for regulating cell migration under both inflammatory and physiological conditions. The first teleost chemokine gene was reported in rainbow trout in 1998. Since then, numerous chemokine genes have been identified in diverse fish species evidencing the great differences that exist among fish and mammalian chemokines, and within the different fish species, as a consequence of extensive intrachromosomal gene duplications and different infectious experiences. Subsequently, it has only been possible to establish clear homologies with mammalian chemokines in the case of some chemokines with well-conserved homeostatic roles, whereas the functionality of other chemokine genes will have to be independently addressed in each species. Despite this, functional studies have only been undertaken for a few of these chemokine genes. In this review, we describe the current state of knowledge of chemokine biology in teleost fish. We have mainly focused on those species for which more research efforts have been made in this subject, specifically zebrafish (Daniorerio), rainbow trout (Oncorhynchusmykiss) and catfish (Ictaluruspunctatus), outlining which genes have been identified thus far, highlighting the most important aspects of their expression regulation and addressing any known aspects of their biological role in immunity. Finally, we summarise what is known about the chemokine receptors in teleosts and provide some analysis using recently available data to help characterise them more clearly.

Yersinia ruckeri, the causative agent of enteric redmouth disease in fish

Enteric redmouth disease (ERM) is a serious septicemic bacterial disease of salmonid fish species. It is caused by Yersinia ruckeri, a Gram-negative rod-shaped enterobacterium. It has a wide host range, broad geographical distribution, and causes significant economic losses in the fish aquaculture industry. The disease gets its name from the subcutaneous hemorrhages, it can cause at the corners of the mouth and in gums and tongue. Other clinical signs include exophthalmia, darkening of the skin, splenomegaly and inflammation of the lower intestine with accumulation of thick yellow fluid. The bacterium enters the fish via the secondary gill lamellae and from there it spreads to the blood and internal organs. Y. ruckeri can be detected by conventional biochemical, serological and molecular methods. Its genome is 3.7 Mb with 3406–3530 coding sequences. Several important virulence factors of Y. ruckeri have been discovered, including haemolyin YhlA and metalloprotease Yrp1. Both non-specific and specific immune responses of fish during the course of Y. ruckeri infection have been well characterized. Several methods of vaccination have been developed for controlling both biotype 1 and biotype 2 Y. ruckeri strains in fish. This review summarizes the current state of knowledge regarding enteric redmouth disease and Y. ruckeri: diagnosis, genome, virulence factors, interaction with the host immune responses, and the development of vaccines against this pathogen.

Evaluation of dual nasal delivery of infectious hematopoietic necrosis virus and enteric red mouth vaccines in rainbow trout (Oncorhynchus mykiss)

Farmed fish are susceptible to different infectious disease agents including viruses and bacteria. Thus, multivalent vaccines or vaccination programs against two or more pathogens are valuable tools in aquaculture. Recently, nasal vaccines have been shown to be very effective in rainbow trout. The current study investigates, for the first time, the use of the nasal route in dual vaccination trials against two important aquatic diseases, infectious hematopoietic necrosis virus (IHN) and enteric red mouth (ERM) disease. Rainbow trout received live attenuated IHN virus (IHNV) vaccine and the ERM bacterin using four different vaccine delivery methods and were challenged with virulent IHNV or Yersinia ruckeri 7 (100 deg day) and 28 (400 deg day) days post-vaccination. The highest survival rates against IHNV at day 7 were obtained by nasal vaccination either when IHNV and ERM were delivered separately into each nare or when they were premixed and delivered to both nasal rosettes (group D). Protection at 28 days against IHNV was similar in all four vaccinated groups. Early protection against ERM was highest in fish that received each vaccine in separate nares (group B), whereas protection at 28 days was highest in the i.p. vaccinated group (group E), followed by the nasally vaccinated group (group B). Survival results were supported by histological observations of the left and right olfactory organ which showed strong immune responses one day (14 deg days) after vaccination in group B vaccinated fish. These data indicate that dual vaccination against two different pathogens via the nasal route is a very effective vaccination strategy for use in aquaculture, particularly when each nare is used separately during delivery. Further long-term studies should evaluate the contribution of adaptive immunity to the protection levels observed.

Nasal immunity is an ancient arm of the mucosal immune system of vertebrates

The mucosal surfaces of all vertebrates have been exposed to similar evolutionary pressures for millions of years. In terrestrial vertebrates such as birds and mammals, the nasopharynx-associated lymphoid tissue (NALT) represents a first line of immune defence. Here we propose that NALT is an ancient arm of the mucosal immune system not restricted to terrestrial vertebrates. We find that NALT is present in rainbow trout and that it resembles other teleost mucosa-associated lymphoid tissues. Trout NALT consists of diffuse lymphoid cells and lacks tonsils and adenoids. The predominant B-cell subset found in trout NALT are IgT(+) B cells, similar to skin and gut. The trout olfactory organ is colonized by abundant symbiotic bacteria, which are coated by trout secretory immunoglobulin. Trout NALT is capable of mounting strong anti-viral immune responses following nasal delivery of a live attenuated viral vaccine. Our results open up a new tool for the control of aquatic infectious diseases via nasal vaccination.

Transfer of serum and cells from Yersinia ruckeri vaccinated doubled-haploid hot creek rainbow trout into outcross F1 progeny elucidates mechanisms of vaccine-induced protection

Yersinia ruckeri is a well-established bacterial pathogen for many salmonid species, against which a formalin-killed bacterin vaccine has been effective in reducing disease outbreaks. Previous studies have reported conflicting results about the protective value of the systemic humoral response to Y. ruckeri vaccination. Here we directly demonstrate that plasma contains the long-term protective component elicited by both immersion and intraperitoneal injection vaccination of rainbow trout. A total of 0.5 μL of plasma from vaccinated fish provided almost complete protection against experimental challenge. Conversely, the cells obtained from peripheral blood conferred little or no protection in naïve recipients. The protective component of immune sera was IgM based on size exclusion chromatography and recognition by monoclonal antibody Warr 1-14. Immune plasma generated against a Y. ruckeri biotype 1 strain protected equally against challenges with Y. ruckeri biotype 1 and 2 strains. These results illustrate the importance of the humoral IgM response against Y. ruckeri and the use of doubled haploid rainbow trout (Oncorhynchus mykiss) and transfer of plasma/serum and cells into F1 outcross progeny as a model system for dissection of the mechanism(s) of vaccine-induced protection.

Immunity to betanodavirus infections of marine fish

Betanodaviruses cause viral nervous necrosis in numerous fish species, but some species are resistant to infection by these viruses. It is essential to fully characterize the immune responses that underlie this protective response. Complete characterization of the immune responses against nodaviruses may allow the development of methods that stimulate fish immunity and of an effective betanodavirus vaccine. Such strategies could include stimulation of specific immune system responses or blockage of factors that decrease the immune response. The innate immune system clearly provides a front-line defense, and this includes the production of interferons and other cytokines. Interferons that are released inside infected cells and that suppress viral replication may be the most ancient form of innate immunity. This review focuses on the immune responses of fish to betanodavirus infection.

Phylogenetic analysis of vertebrate CXC chemokines reveals novel lineage specific groups in teleost fish

In this study, we have identified 421 molecules across the vertebrate spectrum and propose a unified nomenclature for CXC chemokines in fish, amphibians and reptiles based on phylogenetic analysis. Expanding on earlier studies in teleost fish, lineage specific CXC chemokines that have no apparent homologues in mammals were confirmed. Furthermore, in addition to the two subgroups of the CXCL8 homologues known in teleost fish, a third group was identified (termed CXCL8_L3), as was a further subgroup of the fish CXC genes related to CXCL11. Expression of the CXC chemokines found in rainbow trout, Oncorhynchus mykiss, was studied in response to stimulation with inflammatory and antiviral cytokines, and bacterial. Tissue distribution analysis revealed distinct expression profiles for these trout CXC chemokines. Lastly three of the trout chemokines, including two novel fish specific CXC chemokines containing three pairs of cysteines, were produced as recombinant proteins and their effect on trout leucocyte migration studied. These molecules increased the relative expression of CD4 and MCSFR in migrated cells in an in vitro chemotaxis assay.

CsCXCe1: A novel Cynoglossus semilaevis CXC chemokine that functions as a chemoattractant and an immunomodulator for peripheral blood leukocytes

Chemokines are small cytokines that, based on their structural differences, are classified into four groups, one of which is called CXC chemokines. In this study, we identified a CXC chemokine, CsCXCe1, from half-smooth tongue sole (Cynoglossus semilaevis) and analyzed its function. The deduced amino acid sequence of CsCXCe1 contains 115 residues and is phylogenetically distinct from known CXC chemokines. CsCXCe1 possesses the conserved RCXC motif in the form of RCWC but lacks the ELR sequence that is found in some CXC chemokines. Expression of CsCXCe1 as determined by quantitative real time RT-PCR occurred abundantly in immune organs and was upregulated by bacterial and viral infection in time dependent manners. Purified recombinant CsCXCe1 (rCsCXCe1) exhibited comparable chemotactic activities against tongue sole and turbot (Scophthalmus maximus) peripheral blood leukocytes (PBL). Microscopic analysis identified lymphocytes as the major cellular population in PBL that responds to rCsCXCe1. Mutational study showed that when the two cysteine residues in the RCWC motif of CsCXCe1 were substituted by serine, the chemoattractive activity of CsCXCe1 was completely lost. Further study showed that treatment of PBL with rCsCXCe1 (i) stimulated cellular proliferation and respiratory burst activity, (ii) upregulated the expression of a wide spectrum of immune relevant genes, and (iii) enhanced cellular resistance against bacterial infection. Taken together, these results indicate that CsCXCe1 is likely a new type of CXC chemokine that exerts chemotactic and immunostimulatory effects on PBL.

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.

17Beta-estradiol affects the response of complement components and survival of rainbow trout (Oncorhynchus mykiss) challenged by bacterial infection

Research on the endocrine role of estrogens has focused on the reproductive system, while other potential target systems have been less studied. Here, we investigated the possible immunomodulating role of 17β-estradiol (E2) using rainbow trout (Oncorhynchus mykiss) as a model. The aims of the study were to examine a) whether estrogens can modulate immune gene transcription levels, and b) whether this has functional implications for the resistance of trout towards pathogens. Trout were reared from fertilization until 6 months of age under (1) control conditions, (2) short-term E2-treatment (6-month-old juveniles were fed a diet containing 20 mg E2/kg for 2 weeks), or c) long-term E2-treatment (twice a 2-h-bath-exposure of trout embryos to 400 μg 17β-estradiol (E2)/L, followed by rearing on the E2-spiked diet from start-feeding until 6 months of age). Analysis of plasma estrogen levels indicated that the internal estrogen concentrations of E2-exposed fish were within the physiological range and analysis of hepatic vitellogenin mRNA levels indicated that the E2 administration was effective in activating the endogenous estrogen receptor pathway. However, expression levels of the hepatic complement components C3-1, C3-3, and Factor H were not affected by E2-treatment. In a next step, 6-month-old juveniles were challenged with pathogenic bacteria (Yersinia ruckeri). In control fish, this bacterial infection resulted in significant up-regulation of the mRNA levels of hepatic complement genes (C3-1, C3-3, Factor B, Factor H), while E2-treated fish showed no or significantly lower up-regulation of the complement gene transcription levels. Apparently, the E2-treated trout had a lower capacity to activate their immune system to defend against the bacterial infection. This interpretation is corroborated by the finding that survival of E2-treated fish under bacterial challenge was significantly lower than in the control group. In conclusion, the results from this study suggest that estrogens are able to modulate immune parameters of trout with functional consequences on their ability to cope with pathogens.

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.

Specific regulation of the chemokine response to viral hemorrhagic septicemia virus at the entry site

The fin bases constitute the main portal of rhabdovirus entry into rainbow trout (Oncorhynchus mykiss), and replication in this first site strongly conditions the outcome of the infection. In this context, we studied the chemokine response elicited in this area in response to viral hemorrhagic septicemia virus (VHSV), a rhabdovirus. Among all the rainbow trout chemokine genes studied, only the transcription levels of CK10 and CK12 were significantly upregulated in response to VHSV. As the virus had previously been shown to elicit a much stronger chemokine response in internal organs, we compared the effect of VHSV on the gills, another mucosal site which does not constitute the main site of viral entry or rhabdoviral replication. In this case, a significantly stronger chemokine response was triggered, with CK1, CK3, CK9, and CK11 being upregulated in response to VHSV and CK10 and CK12 being down-modulated by the virus. We then conducted further experiments to understand how these different chemokine responses of mucosal tissues could correlate with their capacity to support VHSV replication. No viral replication was detected in the gills, while at the fin bases, only the skin and the muscle were actively supporting viral replication. Within the skin, viral replication took place in the dermis, while viral replication was blocked within epidermal cells at some point before protein translation. The different susceptibilities of the different skin layers to VHSV correlated with the effect that VHSV has on their capacity to secrete chemotactic factors. Altogether, these results suggest a VHSV interference mechanism on the early chemokine response at its active replication sites within mucosal tissues, a possible key process that may facilitate viral entry.

CXCL8 chemokines in teleost fish: two lineages with distinct expression profiles during early phases of inflammation

BACKGROUND

During the inflammatory process, chemokine CXCL8 plays a pivotal role in recruitment of human neutrophilic granulocytes. A diversity of sequences similar to CXCL8 was reported in fish, but their evolutionary relationships and functional homology with their human homolog remain unclear.

PRINCIPAL FINDINGS

We screened fish genomes to seek for sequences related to CXCL8. A first lineage was retrieved in all teleosts, while a second CXCL8 lineage was found in zebrafish and carp only. An early inflammatory function for both lineages was indicated by several lines of evidence. The induction of carp CXCL8s, CXCb, and CXC receptor-1 and -2 was analyzed after in vitro stimulation of leukocyte subpopulations and in two in vivo inflammation models. Recombinant proteins of carp CXCL8 proteins were produced and showed significant chemotactic activity for carp leukocytes.

CONCLUSIONS

While both carp CXCL8s appear to be functional homologs of mammalian CXCL8, their different induction requirements and kinetics evoke a gene-specific sub-functionalization.

Viral hemorrhagic septicemia and infectious pancreatic necrosis viruses replicate differently in rainbow trout gonad and induce different chemokine transcription profiles

Viral hemorrhagic septicemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV) are two rainbow trout (Oncorhynchus mykiss) pathogens. While IPNV is known to be vertically transmitted to the next generation through the oocyte, VHSV is known to replicate in the ovary and be transmitted horizontally through the ovarian fluid. In this work, we wanted to study whether these differences had an effect on the immune response triggered in the ovary, with a focus on the chemokine response. We have studied the kinetics of viral gene expression and the sites of replication, confirming that great differences exist between the replication of the two viruses in the gonad. Next, we studied the levels of expression of several CXC and CC chemokines in the ovary and found that while VHSV strongly triggered chemokine transcription, IPNV had almost no effect. This lack of immune response might be an advantage that permits its vertical transmission.

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.

Innate immune response in rainbow trout (Oncorhynchus mykiss) against primary and secondary infections with Yersinia ruckeri O1

Response mechanisms in teleosts against bacterial pathogens have been widely studied following injection procedures applying preparations of killed bacteria. In contrast, investigations on immune reactions in fish which have survived a primary infection and subsequently have been challenged are few or lacking. However, knowledge on these factors during infection and re-infection could provide the basis for development of improved vaccines. The innate immune response in rainbow trout (Oncorhynchus mykiss) against Yersinia ruckeri O1 has been studied following a primary intra-peritoneal injection with 5 x 10(5) CFU Y. ruckeri, and after bacterial clearance a secondary infection 35 days later. The number of pathogens in the liver was measured with a Y. ruckeri specific 16S ribosomal RNA quantitative real-time RT-PCR (q-PCR) during the course of infection. The bacterial counts peaked on day 3 during the primary infection and were significantly lower during the re-infection. Re-challenged fish showed a highly increased survival when compared to the naïve fish receiving a primary infection indicating development of adaptive immunity in the fish against this bacterial pathogen. We investigated the gene expression of innate immune factors in the liver during infections in order to elucidate molecules involved in survival of hosts before adaptive immunity was mounted. Transcription of mRNA was measured in liver samples taken 8 h, 1, 3, 7, 14 and 28 d post-infection using q-PCR. The investigation focused on genes encoding toll-like receptor 5 (TLR5), the pro-inflammatory cytokines IL-1beta, IL-6 and TNF-alpha, the acute phase proteins (APPs) serum amyloid protein a (SAA), trout C polysaccharide binding protein, a CRP/SAP like pentraxin, precerebellin, transferrin, hepcidin and finally the complement factors C3, C5 and factor B. Infection elicited significantly increased gene expression of all the cytokines (IL-6 > 1000-fold), some acute phase proteins (SAA > 3000-fold) and down-regulation of complement factors (C3, C5 and factor B). SAA expression was significantly earlier activated during the re-infection when compared to the primary infection. The pattern of gene activation suggested that the innate response was based on pathogen binding to toll-like receptors, production of cytokines and subsequent release of APPs. In general, both the innate immune response and the amount of Y. ruckeri measured in the liver during the re-infection was much lower compared to the first infection, probably reflecting development of adaptive immunity.

Cloning and bioactivity analysis of a CXC ligand in black seabream Acanthopagrus schlegeli: the evolutionary clues of ELR+CXC chemokines

Background

The ELR⁺CXC chemokines are multifunctional mediators that are mainly responsible for the recruitment of leucocytes to sites of inflammation and infection. Because of their high sequence identity with mammalian IL-8, fish IL-8-like CXCs have been named as piscine 'IL-8' and included in the ELR⁺ subgroup, even though there is no reliable functional or evolutionary evidence to support this classification.

Results

In this investigation, a homologue of piscine 'IL-8' from black seabream (Acanthopagrus schlegeli), called BS CXC, has been cloned and analyzed. The results revealed that BS CXC has a high gene similarity and tertiary structure similarity with piscine and mammalian CXC chemokines, both ELR^-CXC and ELR⁺CXC, although it has a lower identity with ELR^-CXC, compared with ELR⁺CXC chemokines. Like other piscine IL-8, BS CXC has only an incomplete ELR motif, which is essential for the mammalian ELR⁺CXC ability to attract granulocytes. Bioactivity assay demonstrated that the BS rCXC produced in E. coli significantly stimulated migration of fish neutrophils and macrophages, but had no effect on rat neutrophils and macrophages, whereas hrIL-8 induced strong chemotaxis of fish neutrophils but did not affect fish macrophages. BS CXC seems show some structural and functional properties of the intermediate between ELR^-CXC and ELR⁺CXC.

Conclusion

As an incomplete ELR⁺CXC chemokine from a modern fish, BS CXC provides some clues on the evolution from ancient ELR^-CXC to ELR⁺CXC by retaining some properties of the intermediate stage in evolution, and it may be more appropriate to call this molecule 'piscine CXC with an incomplete ELR', instead of terming it fish 'IL-8'.

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.

Extensive expansion and diversification of the chemokine gene family in zebrafish: identification of a novel chemokine subfamily CX

Background

The chemokine family plays important roles in cell migration and activation. In humans, at least 44 members are known. Based on the arrangement of the four conserved cysteine residues, chemokines are now classified into four subfamilies, CXC, CC, XC and CX3C. Given that zebrafish is an important experimental model and teleost fishes constitute an evolutionarily diverse group that forms half the vertebrate species, it would be useful to compare the zebrafish chemokine system with those of mammals. Prior to this study, however, only incomplete lists of the zebrafish chemokine genes were reported.

Results

We systematically searched chemokine genes in the zebrafish genome and EST databases, and identified more than 100 chemokine genes. These genes were CXC, CC and XC subfamily members, while no CX3C gene was identified. We also searched chemokine genes in pufferfish fugu and Tetraodon, and found only 18 chemokine genes in each species. The majority of the identified chemokine genes are unique to zebrafish or teleost fishes. However, several groups of chemokines are moderately similar to human chemokines, and some chemokines are orthologous to human homeostatic chemokines CXCL12 and CXCL14. Zebrafish also possesses a novel species-specific subfamily consisting of five members, which we term the CX subfamily. The CX chemokines lack one of the two N-terminus conserved cysteine residues but retain the third and the fourth ones. (Note that the XC subfamily only retains the second and fourth of the signature cysteines residues.) Phylogenetic analysis and genome organization of the chemokine genes showed that successive tandem duplication events generated the CX genes from the CC subfamily. Recombinant CXL-chr24a, one of the CX subfamily members on chromosome 24, showed marked chemotactic activity for carp leukocytes. The mRNA was expressed mainly during a certain period of the embryogenesis, suggesting its role in the zebrafish development.

Conclusion

The phylogenic and genomic organization analyses suggest that a substantial number of chemokine genes in zebrafish were generated by zebrafish-specific tandem duplication events. During such duplications, a novel chemokine subfamily termed CX was generated in zebrafish. Only two human chemokines CXCL12 and CXCL14 have the orthologous chemokines in zebrafish. The diversification observed in the numbers and sequences of chemokines in the fish may reflect the adaptation of the individual species to their respective biological environment.

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.

Early diversification of the TNF superfamily in teleosts: genomic characterization and expression analysis

The TNF superfamily (TNFSF) of proteins are cytokines involved in diverse immunological and developmental pathways. Little is known about their evolution or expression in lower vertebrate species. Bioinformatic searches of Zebrafish, Tetraodon, and Fugu genome and other teleost expressed sequence tag databases identified 44 novel gene sequences containing a TNF homology domain. This work reveals the following: 1) teleosts possess orthologs of BAFF, APRIL, EDA, TWEAK, 4-1BBL, Fas ligand, LIGHT, CD40L, RANKL, and possibly TL1A; 2) the BAFF-APRIL subfamily is enriched by a third member, BALM, unique to fish; 3) orthologs of lymphotoxins alpha and beta were not clearly identified in teleosts and are substituted by a related ligand, TNF-New; 4) as many as four TRAIL-like genes are present in teleosts, as compared with only one in mammals; and 5) T cell activation ligands OX40L, CD27L, CD30L, and GITRL were not identified in any fish species. Finally, we characterize mRNA expression of TNFSF members CD40L, LIGHT, BALM, APRIL, Fas ligand, RANKL, TRAIL-like, and TNF-New in rainbow trout, Oncorhynchus mykiss, immune and nonimmune tissues. In conclusion, we identified a total of 14 distinct TNFSF members in fishes, indicating expansion of this superfamily before the divergence of bony fish and tetrapods, approximately 360-450 million years ago. Based on these findings, we extend a model of TNFSF evolution and the co-emergence of the vertebrate adaptive immune system.

Yersinia ruckeri infections in salmonid fish

Yersinia ruckeri is the causative agent of yersiniosis or enteric redmouth disease leading to significant economic losses in salmonid aquaculture worldwide. Infection may result in a septicaemic condition with haemorrhages on the body surface and in the internal organs. Despite the significance of the disease, very little information is available on the pathogenesis, hampering the development of preventive measures to efficiently combat this bacterial agent. This review discusses the agent and the disease it causes. The possibility of the presence of similar virulence markers and/or pathogenic mechanisms between the Yersinia species which elicit disease in humans and Y. ruckeri is also examined.