Identification of six novel CC chemokines in gilthead seabream (Sparus aurata) implicated in the antiviral immune response

Molecular cytogenetic analysis of the olive flounder embryonic cell line FGBC8 and its applicability to biotechnology

We explored the biotechnological applicability of a previously established olive flounder (Paralichthys olivaceus) embryonic cell line (FGBC8). FGBC8 was transfected with pEGFP-c1 and pluripotency-related genes, then infected with viral hemorrhagic septicemia virus (VHSV), and the expression of immune-related genes was observed through quantitative real-time polymerase chain reaction. Transfected cells showed strong green fluorescence 48 h after transfection, and pluripotency-related genes were successfully transfected. In addition, FGBC8 cells were highly susceptible to VHSV and the expression of immune-related genes was induced during infection. Our results demonstrate that FGBC8 cells are valuable research tools for assessing host-pathogen interactions and biotechnological applications.

Two CcCCL19bs orchestrate an antibacterial immune response in Yellow River carp (Cyprinus carpio haematopterus)

Chemokines are a group of chemotactic cytokines with an essential role in homeostasis as well as immunity via specific G protein-coupled receptors and atypical receptors. In our study, two Yellow River carp (Cyprinus carpio haematopterus) CCL19b genes (CcCCL19bs), tentatively named CcCCL19b_a and CcCCL19b_b, were cloned. The open reading frames (ORFs) of CcCCL19b_a and CcCCL19b_b were both 333 bp that encoded a 12 kDa protein with 110 amino acid residues. CcCCL19bs contained a signal peptide and a SCY domain with four typical conserved cysteine residues. The two CcCCL19b proteins shared high similarities with each other in both secondary and three-dimensional structure. Phylogenetic analysis showed that CcCCL19bs and other CCL19bs from tetraploid cyprinid fish were clustered into one clade. CcCCL19bs were highly expressed in gill and intestine in healthy fish, and a significant up-regulation of gene expression after Aeromonas hydrophila infection and poly(I:C) stimulation was observed in gill, liver, and head kidney. Furthermore, chemotaxis and antibacterial activity of CcCCL19bs were studied. The results indicated that recombinant CcCCL19b_a and CcCCL19b_b protein (rCcCCL19b_a and rCcCCL19b_b) exhibited significant attraction to primary head kidney leukocytes (HKLs). Meanwhile, both of rCcCCL19bs could promote the proliferation of HKLs, and significantly up-regulate the expressions of IL-1β, CCR7, and IL-6, and down-regulate the expression of IL-10 in primary HKLs. In vitro, rCcCCL19bs could bind and aggregate A. hydrophila and Staphylococcus aureus. The rCcCCL19bs exhibited significant antibacterial activity against A. hydrophila, but not S. aureus. Moreover, they inhibited the growth of A. hydrophila and S. aureus. In vivo, overexpression of CcCCL19bs contributed to the bacterial clearance. These studies suggested that CcCCL19bs orchestrate an antibacterial immune response.

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.

Immune response of DNA vaccinated-gilthead seabream (Sparus aurata) against LCDV-Sa infection: relevance of the inflammatory process

Lymphocystis disease is one of the main viral pathologies affecting cultured gilthead seabream (Sparus aurata) in the Mediterranean region. Recently, we have developed a DNA vaccine based on the major capsid protein (MCP) of the Lymphocystis disease virus 3 (LCDV-Sa). The immune response triggered by either LCDV-Sa infection or vaccination have been previously studied and seem to be highly related to the modulation of the inflammatory and the IFN response. However, a comprehensive evaluation of immune-related gene expression in vaccinated fish after viral infection to identify immunogenes involved in vaccine-induced protection have not been carried out to date. The present study aimed to fulfill this objective by analyzing samples of head-kidney, spleen, intestine, and caudal fin from fish using an OpenArray® platform containing targets related to the immune response of gilthead seabream. The results obtained showed an increase of deregulated genes in the hematopoietic organs between vaccinated and non-vaccinated fish. However, in the intestine and fin, the results showed the opposite trend. The global effect of fish vaccination was a significant decrease (p<0.05) of viral replication in groups of fish previously vaccinated, and the expression of the following immune genes related to viral recognition (tlr9), humoral and cellular response (rag1 and cd48), inflammation (csf1r, elam, il1β, and il6), antiviral response (isg15, mx1, mx2, mx3), cell-mediated cytotoxicity (nccrp1), and apoptosis (prf1). The exclusive modulation of the immune response provoked by the vaccination seems to control the progression of the infection in the experimentally challenged gilthead seabream.

Modulation of gut microbiota and intestinal immune response in gilthead seabream (Sparus aurata) by dietary bile salt supplementation

Given their role in lipid digestion, feed supplementation with bile salts could be an economic and sustainable solution to alterations in adiposity and intestinal inflammation generated by some strategies currently used in aquaculture. An important part of the metabolism of bile salts takes place in the intestine, where the microbiota transforms them into more toxic forms. Consequently, we aimed to evaluate the gut immune response and microbial populations in gilthead seabream (Sparus aurata) fed a diet supplemented with a blend of bile salts with proven background as a regulator of lipid metabolism and fat content. After the 90-day feeding trial, a differential modulation of the microbiota between the anterior and posterior intestine was observed. While in the anterior intestine the relative abundance of Desulfobacterota doubled, in the posterior intestine, the levels of Firmicutes increased and Proteobacteria, Actinobacteriota, and Campylobacterota were reduced when supplementing the diet with bile salts. Even so, only in the anterior intestine, there was a decrease in estimated richness (Chao1 and ACE indices) in presence of dietary bile salts. No significant differences were displayed in alpha (Shannon and Simpson indices) nor beta-diversity, showing that bile sales did not have a great impact on the intestinal microbiota. Regarding the gene expression profile in 2 h postprandial-fish, several changes were observed in the analyzed biomarkers of epithelial integrity, nutrient transport, mucus production, interleukins, cell markers, immunoglobulin production and pathogen recognition receptors. These results may indicate the development of an intestinal immune-protective status to tackle future threats. This work also suggests that this immune response is not only regulated by the presence of the dietary bile salts in the intestine, but also by the microbial populations that are in turn modulated by bile salts. After a fasting period of 2 days, the overall gene expression profile was stabilized with respect to fish fed the unsupplemented diet, indicating that the effect of bile salts was transient after short periods of fasting. On the balance, bile salts can be used as a dietary supplement to enhance S. aurata farming and production without compromising their intestinal health.

A novel C1qDC (PoC1qDC) with a collagen domain in Paralichthys olivaceus mediates complement activation and against bacterial infection

Complement C1q domain containing protein (C1qDC) is a vital recognition molecule and has an important effect on immunity. The C1qDCs exhibit opsonic activity in fish, while the mechanisms of C1qDCs in activation complement still remain unclear. This study explored immunological characteristics of a C1qDC from Japanese flounder (Paralichthys olivaceus) (PoC1qDC). PoC1qDC consists of 296 amino acid residues, possessing a collagen domain and a C1q domain. According to our results, PoC1qDC was expressed in 9 diverse tissue samples and showed up-regulation after bacterial challenge. Recombinant PoC1qDC (rPoC1qDC) activated normal serum bactericidal and hemolytic activities by interaction with Japanese flounder IgM, but not enhanced the complement activity of C3-depeleted serum. rPoC1qDC was significantly bound to various bacterial species and agglutination activity against Edwardsiella piscicida and Streptococcus iniae. Furthermore, rPoC1qDC showed direct interaction with peripheral blood leucocytes while enhancing phagocytic and chemotactic activity. When PoC1qDC was overexpressed in Japanese flounder before E. piscicida infection, bacterial replication was significantly inhibited in fish tissues. Consistently, when PoC1qDC expression in Japanese flounder was knocked down, bacterial replication was significantly enhanced. The above findings first suggested the role of PoC1qDC in teleost in mediating complement activation by interaction with IgM, which can positively influence bacterial infection.

Time-course transcriptome analyses of spleen in rainbow trout (Oncorhynchus mykiss) post-Flavobacterium psychrophilum infection

Flavobacterium psychrophilum, the etiological agent of bacterial coldwater disease and rainbow trout fry syndrome, causes considerable losses in salmonid aquaculture globally. Systemic F. psychrophilum infections in rainbow trout (Oncorhynchus mykiss) lead to a range of clinical signs, including ulcerative lesions in the skin and muscle and splenitis. Previous studies offered an integrative analysis of the skeletal muscle response to F. psychrophilum infection in rainbow trout. However, little is known about the molecular mechanism of immune response in the spleen, which is an important immune organ of rainbow trout. Here, we investigated the time-course splenic transcriptome profiles in uninfected rainbow trout (CK) and F. psychrophilum–infected rainbow trout at day 3 and day 7 (D3, D7) by RNA-seq analyses. Among the 7,170 differentially expressed genes (DEGs) in the three comparisons (D3 vs. CK, D7 vs. CK, D3 vs. D7), 1,286 DEGs showed consistent upregulation or downregulation at D3 and D7 and were associated with pattern recognition, acute-phase response, complement cascade, chemokine and cytokine signaling, and apoptosis. The Real time quantitative PCR (RT-qPCR) analysis of eight DEGs confirmed the accuracy of the RNA-Sequencing (RNA-seq) data. Our results reflected a general process from pathogen recognition to inflammatory cytokine generation and delineated a putative Toll-like receptor signaling pathway in rainbow trout spleen, following F. psychrophilum infection. Taken together, these results provide new insights into the molecular mechanism of the immune response to F. psychrophilum infection and are a valuable resource for future research on the prevention and control of bacterial coldwater disease during salmon culture.

CC chemokine 1 protein from Cromileptes altivelis (CaCC1) promotes antimicrobial immune defense

Chemokines are a family of small signaling proteins that are secreted by various cells. In addition to their roles in immune surveillance, localization of antigen, and lymphocyte trafficking for the maintenance of homeostasis, chemokines also function in induce immune cell migration under pathological conditions. In the present study, a novel CC chemokine gene (CaCC1) from humpback grouper (Cromileptes altivelis) was cloned and characterized. CaCC1 comprised a 435 bp open reading frame encoding 144 amino acid residues. The putative molecular weight of CaCC1 protein was 15 kDa CaCC1 contains four characteristic cysteines that are conserved in other known CC chemokines. CaCC1 also shares 11.64%-90.28% identity with other teleost and mammal CC chemokines. Phylogenetic analysis revealed that CaCC1 is most closely related to Epinephelus coioides EcCC1, both of which are in a fish-specific CC chemokine clade. CaCC1 was constitutively expressed in all examined C. altivelis tissues, with high expression levels in skin, heart, liver, and intestine. Vibrio harveyi stimulation up-regulated CaCC1 expression levels in liver, spleen, and head-kidney. Functional analyses revealed that the recombinant protein (rCaCC1) could induce the migration of head-kidney lymphocytes from C. altivelis. Moreover, rCaCC1 significantly enhanced phagocytosis in head-kidney macrophages from C. altivelis. In addition, rCaCC1 exhibited antimicrobial activities against Staphylococcus aureus, Edwardsiella tarda, and V. harveyi. In vivo, CaCC1 overexpression improved bacterial clearance in V. harveyi infected fish. Conversely, CaCC1 knockdown resulted in a significant decrease of bacterial clearance. These results demonstrate the important roles that CaCC1 plays in homeostasis and in inflammatory response to bacterial infection.

Complement C3 and Activated Fragment C3a Are Involved in Complement Activation and Anti-Bacterial Immunity

In the complement system, C3 is a central component in complement activation, immune defense and immune regulation. In all pathways of complement activation, the pivotal step is conversion of the component C3 to C3b and C3a, which is responsible to eliminate the pathogen and opsonization. In this study, we examined the immunological properties of C3 and its activated fragment C3a from Japanese flounder (Paralichthys olivaceus) (PoC3 and PoC3a), a teleost species with important economic value. PoC3 is composed of 1655 amino acid residues, contains the six domains and highly conserved GCGEQ sequence of the C3 family. We found that PoC3 expression occurred in nine different tissues and was upregulated by bacterial challenge. In serum, PoC3 was able to bind to a broad-spectrum of bacteria, and purified native PoC3 could directly kill specific pathogen. When PoC3 expression in Japanese flounder was knocked down by siRNA, serum complement activity was significantly decreased, and bacterial replication in fish tissues was significantly increased. Recombinant PoC3a (rPoC3a) exhibited apparent binding capacities to bacteria and Japanese flounder peripheral blood leukocytes (PBL) and induce chemotaxis of PBL. Japanese flounder administered rPoC3a exhibited enhanced resistance against bacterial infection. Taken together, these results indicate that PoC3 is likely a key factor of complement activation, and PoC3 and PoC3a are required for optimal defense against bacterial infection in teleost.

A CCL25 chemokine functions as a chemoattractant and an immunomodulator in black rockfish, Sebastes schlegelii

Chemokines are small cytokines that are classified into four groups, one of which is called CC chemokines. In the present study, the full-length cDNA of a CCL25 chemokine was identified from black rockfish, Sebastes schlegelii (named as SsCCL25) by EST (expressed sequence tag) analysis. The cDNA of SsCCL25 consisted of a 5-terminal untranslated region (UTR) of 74 bp, a 3-UTR of 882 bp with a poly (A) tail, and an open reading frame (ORF) of 303 bp encoding a polypeptide of 100 amino acids with the putative molecular mass of 11.5 kDa. There was a SCY domain in the deduced amino acid sequence of SsCCL25. The phylogenetic relationships and syntenic analyses provided evidences for the identities of SsCCL25 with CCL25 group. The mRNA transcripts of SsCCL25 were expressed in all detected tissues and dominantly in liver, muscle and gill. Moreover, after Vibrio anguillarum stimulation, the mRNA expression levels of SsCCL25 were significantly up-regulated at 24 h (p < 0.05) in the liver and during 4-8 h (p < 0.05) in the spleen. Recombinant SsCCL25 protein induced chemotaxis of both control and LPS-stimulated peripheral blood leukocytes (PBL) and enhanced their resistance to bacterial infection in a dose-dependent manner. Furthermore, rSsCCL25 showed significant inhibitory effect on V. anguillarum and Edwardsiella tarda growth. All these results collectively indicated that SsCCL25 might contribute to the defense against microbe infection and function as a chemoattractant in black rockfish.

Dual RNA-Seq uncovers the function of an ABC transporter gene in the host-pathogen interaction between Epinephelus coioides and Pseudomonas plecoglossicida

As an important pathogen in aquaculture, Pseudomonas plecoglossicida has caused heavy losses. The expression of an ABC transporter gene-L321_23611 of P. plecoglossicida at 18 °C was found significant higher than those at 28 °C by RNA-seq and qRT-PCR. RNAi significantly reduced the content of L321_23611 mRNA in P. plecoglossicida with a maximal decrease of 89.2%. Compared with the wild type strain, the infection of L321_23611-RNAi strain resulted in the reduction in mortality and the onset time delay of a kind of marine teleosts, Epinephelus coioides. The results of dual RNA-seq showed that the RNAi of L321_23611 resulted in a significant change in both pathogen and host transcriptome in the spleens of infected E. coioides. The result of GO and KEGG analysis from dual RNA-seq data showed both host genes of chemokine signaling pathway, coagulation and complement system, hematopoietic cell lineage pathway as well as hemoglobin complex GO term and pathogenic genes of bacterial-type flagellum-dependent cell mortality GO term and flagellar assembly, biosynthesis of amino acids and lysine biosynthesis systems pathways were mainly affected by L321_23611 gene of P. plecoglossicida. The results indicated that: 1. ABC transporter gene-L321_23611 was a virulent gene of P. plecoglossicida. 2. Both the activation of the host immune pathways and depression of pathogenic virulence-related pathways facilitated E. coioides to remove L321_23611-RNAi strain than the wild type strain of P. plecoglossicida.

Identification and expression analysis of 19 CC chemokine genes in orange-spotted grouper (Epinephelus coioides)

In this study, we describe 19 different CC chemokine genes from the orange-spotted grouper, Epinephelus coioides, identified by the analysis of the spleen transcriptome. Multiple sequence alignment of the 19 CC chemokines showed that although two genes, EcSCYA115 and EcSCYA117, shared 80% amino acid similarity (72% identity), the majority exhibited low similarity to each other. Phylogenetic analysis divided the 19 CC chemokines into six major groups. Tissue distribution analysis by RT-PCR showed that most of these chemokines were ubiquitously expressed in the 9 examined tissues, whereas some exhibited tissue-preferential expression patterns. For example, EcSCYA103 was preferentially expressed in fin and gill; EcSCYA109 in head kidney and spleen; EcSCYA114 in fin, gill, and liver; and EcSCYA119 in fin and stomach. Quantitative RT-PCR showed that after challenge with grouper iridovirus (GIV), four of the 19 CC chemokine genes, EcSYCA102, EcSYCA103, EcSYCA116, and EcSYCA118, were highly induced in the spleen. The expression of these four genes could also be upregulated by LPS and poly (I:C) challenges, suggesting that these four genes might be involved in immune response against invading pathogens.

TroCCL4, a CC chemokine of Trachinotus ovatus, is involved in the antimicrobial immune response

CC chemokines are a large subfamily of chemokines that play an important role in the innate immune system. To date, several CC chemokines have been identified in fish species; however, the activities and functions of these putative chemokines remain ambiguous in teleosts, especially in the golden pompano, Trachinotus ovatus. Here, we characterized CC chemokine ligand 4 from T. ovatus (TroCCL4) and studied its functions. TroCCL4 contains a 294 bp open reading frame that encodes a putative peptide comprising 97 amino acids. TroCCL4 shares a high amino acid sequence similarity of 31.11%-78.35% with other CC chemokines sequences in humans and teleosts and has four cysteine residues that are conserved among other CC chemokines. TroCCL4 is also related to the macrophage inflammatory protein (MIP) group of CC chemokines. TroCCL4 expression was most abundant in immune organs and significantly upregulated in a time-dependent manner following Edwardsiella tarda infection. Recombinant TroCCL4 (rTroCCL4) induced the migration of peripheral blood leukocytes and the cellular proliferation of head kidney lymphocytes. In addition, rTroCCL4 inhibited the growth of Escherichia coli and E. tarda, indicating an antimicrobial function. Furthermore, the results of in vivo analysis showed that TroCCL4 overexpression in T. ovatus significantly enhanced macrophage activation; upregulated the gene expression of interleukin 1-β (IL-1β), interleukin 15 (IL15), interferon-induced Mx protein (Mx), tumor necrosis factor α (TNFα), complement C3, and major histocompatibility complex (MHC) class Iα and class IIα; and protected against bacterial infection in fish tissues. In contrast, knockdown of TroCCL4 expression resulted in increased bacterial dissemination and colonization in fish tissues. Taken together, our results provide evidence indicating that TroCCL4 has the ability to stimulate leukocytes and macrophages and enhance host immunity to defend against bacterial infection.

Genes related to cell-mediated cytotoxicity and interferon response are induced in the retina of European sea bass upon intravitreal infection with nodavirus

Viral diseases are responsible for high rates of mortality and subsequent economic losses in modern aquaculture. The nervous necrosis virus (NNV) produces viral encephalopathy and retinopathy (VER), which affects the central nervous system, is considered one of the most serious viral diseases in marine aquaculture. Although some studies have localized NNV in the retina cells, none has dealt with immunity in the retina. Thus, for the first time, we intravitreally infected healthy specimens of European sea bass (Dicentrarchus labrax) with NNV with the aim of characterizing the immune response in the retina. Ultrastructural analysis detected important retinal injuries and structure degradation, including pycnosis, hydropic degeneration and vacuolization in some cell layers as well as myelin sheaths in the optic nerve fibres. Immunohistochemistry demonstrated that NNV replicated in the eyes. Regarding retinal immunity, NNV infection elicited the transcription of genes encoding proteins involved in the interferon (IFN) and cell-mediated cytotoxicity (CMC) responses as well as B and T cell markers, demonstrating that viral replication influences innate and adaptive responses. Further studies are needed to understand the retina immunity and whether the main retinal function, vision, is affected by nodavirus.

A mini review on immune role of chemokines and its receptors in snakehead murrel Channa striatus

Chemokines are ubiquitous cytokine molecules involved in migration of cells during inflammation and normal physiological processes. Though the study on chemokines in mammalian species like humans have been extensively studied, characterization of chemokines in teleost fishes is still in the early stage. The present review provides an overview of chemokines and its receptors in a teleost fish, Channa striatus. C. striatus is an air breathing freshwater carnivore, which has enormous economic importance. This species is affected by an oomycete fungus, Aphanomyces invadans and a Gram negative bacteria Aeromonas hydrophila is known to cause secondary infection. These pathogens impose immune changes in the host organism, which in turn mounts several immune responses. Of these, the role of cytokines in the immune response is immense, due to their involvement in several activities of inflammation such as cell trafficking to the site of inflammation and antigen presentation. Given that importance, chemokines in fishes do have significant role in the immunological and other physiological functions of the organism, hence there is a need to understand the characteristics, activities and performace of these small molecules in details.

Molecular characterization, functional analysis, and defense mechanisms of two CC chemokines in Nile tilapia (Oreochromis niloticus) in response to severely pathogenic bacteria

Two full-length cDNAs encoding CC chemokine genes in Nile tilapia (Oreochromis niloticus) (On-CC1 and On-CC2) were cloned and characterized. On-CC1 and On-CC2 showed signature cysteine motifs consisting of four cysteines. The expression levels of On-CC1 and On-CC2 were analyzed by RT-PCR, which showed that low expression of these two genes was only observed in the peripheral blood leukocytes (PBLs) and spleen of normal fish. Expression levels of these two molecules were quantified in 13 tissues of fish infected with virulent strains of Streptococcus agalactiae and Flavobacterium columnare. Most tissues, especially PBLs, the spleen and the liver, expressed significantly higher mRNA levels than the controls, particularly at 12 and 24 h after infection (P < 0.05). The current study strongly indicates that CC chemokine genes in Nile tilapia are crucially involved in the early immune responses to pathogens. Functional analyses clearly demonstrated that 10 and 100 μg/ml of recombinant rOn-CC1 and rOn-CC2 proteins efficiently enhanced the phagocytic activity (in vitro) of Nile tilapia phagocytes. Finally, Southern blot analysis and searching in Ensembl databases demonstrated that two different functional CC chemokine genes and other pseudogene fragments were discovered in the Nile tilapia genome.

Molecular characterization and expression analysis of nine CC chemokines in half-smooth tongue sole, Cynoglossus semilaevis

Chemokines are a large, diverse group of small cytokines that can be classified into several families, including the CC chemokine family, which plays a pivotal role in host defense by inducing leukocyte chemotaxis under physiological and inflammatory conditions. Here we studied 9 CC chemokines from half-smooth tongue sole (Cynoglossus semilaevis). Phylogenetic analysis divided these chemokines into four groups. The tissue specific expression patterns of the 9 chemokines under normal physiological conditions varied much, with most chemokines highly expressed in immune organs, while some other chemokines showing high expression levels in non-immune organs. In addition, the 9 chemokines exhibited similar or distinctly different expression profiles in response to the challenge of virus and intracellular and extracellular bacterial pathogens. These results indicate that in tongue sole, CC chemokines may be involved in different immune responses as homeostatic or inflammatory chemokines.

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.

A CCL21 chemokine of tongue sole (Cynoglossus semilaevis) promotes host resistance against bacterial infection

Chemokines are a large family of chemotactic cytokines. Based on the arrangement of the first two cysteine residues, chemokines are divided into four groups, one of which is the CC chemokine group. In this study, we characterized a CC chemokine, CsCCL21, from half-smooth tongue sole (Cynoglossus semilaevis), and analyzed its activity. CsCCL21 contains two conserved N-terminal cysteine residues in a NCCL motif and is phylogenetically related to the CCL19/21/25 subgroup of CC chemokines. CsCCL21 was constitutively expressed in nine tissues and significantly upregulated by bacterial and viral infection. The recombinant CsCCL21 (rCsCCL21) induced migration of peripheral blood leukocytes. When the two conserved cysteine residues in the NCCL motif were mutated, the chemotactic activity of rCsCCL21 was abolished. rCsCCL21 enhanced the resistance of tongue sole against bacterial infection, but the mutant protein with NCCL mutation lacked this antibacterial effect. Taken together, these results suggest that CsCCL21 is a functional CC chemokine with the ability to recruit leukocytes and is involved in antibacterial immunity in a manner that requires the conserved NCCL motif.

Fish chemokines 14, 20 and 25: A comparative statement on computational analysis and mRNA regulation upon pathogenic infection

In this study, we reported a molecular characterization of three CC chemokines namely, CsCC-Chem14, CsCC-Chem20 and CsCC-Chem25 which are were identified from the established cDNA library of striped murrel Channa striatus. Multiple sequence alignment of all the three chemokines revealed the presence of gene specific domains and motifs including small cytokine domain, IL8 like domain, receptor binding site and glycosaminoglycan (GAG) binding sites. Three dimensional structures of the chemokines under study showed an important facet on their anti-microbial property. Tissue specific mRNA expression showed that the CsCC-Chem14 is highly expressed in spleen, CsCC-Chem20 in liver and CsCC-Chem25 in trunk kidney. On challenge C. striatus with oomycete fungus Aphanomyces invadans, both CsCC-Chem20 and CsCC-Chem25 showed significant (P < 0.05) up-regulation compared to CsCC-Chem14. The increase in the expression levels of CsCC-Chem20 and CsCC-Chem25 due to infection showed that they are antimicrobial proteins. But considering the CsCC-Chem14 expression, it is found to be a constitutive chemokine and is involved in homeostatic function in spleen of C. striatus. C. striatus challenged with bacteria Aeromonas hydrophila also exhibited different up-regulation pattern in all the three chemokines at various time points. However, extensive studies are required to determine the functional activities of CsCC-Chem14, CsCC-Chem20 and CsCC-Chem25 in vitro and in vivo to gain more knowledge at the molecular and proteomic levels.

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

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

Molecular and functional roles of 6C CC chemokine 19 in defense system of striped murrel Channa striatus

In this study, we have reported the molecular information of chemokine-19 (Chem19) from striped murrel Channa striatus (Cs). CsCC-Chem19 cDNA sequence was 555 base pair (bp) in length which is 68bp 5' untranslated region (UTR), 339bp translated region and 149bp 3' UTR. The translated region is encoded for a polypeptide of 112 amino acids. CsCC-Chem19 peptide contains a signal sequence between 1 and 26 and an interleukin (IL) 8 like domain between 24 and 89. The multiple sequence alignment showed a 'DCCL' motif, an indispensable motif present in all CC chemokines which was conserved throughout the evolution. Phylogenetic tree showed that CsCC-Chem19 formed a cluster with chemokine 19 from fishes. Secondary structure of CsCC-Chem19 revealed that the peptide contains maximum amount of coils (61.6%) compared to α-helices (25.9%%) and β-sheet (12.5%). Further, 3D analysis indicated that the cysteine residues at 33, 34, 59 and 75 making the disulfide bridges as 33 = 59 and 34 = 75. Significantly (P < 0.05) highest CsCC-Chem19 mRNA expression was observed in blood and it was up-regulated upon fungus and bacterial infection. Utilizing the coding region of CsCC-Chem19, recombinant CsCC-Chem19 protein was produced. The recombinant CsCC-Chem19 protein induced the cellular proliferation and respiratory burst activity of C. striatus peripheral blood leukocytes (PBL) in a concentration dependent manner. Moreover, the chemotactic activity showed that the recombinant CsCC-Chem19 significantly (P < 0.05) enhanced the movement of PBL of C. striatus. Conclusively, CsCC-Chem19 is a 6C CC chemokine having an ability to perform both inflammatory and homeostatic functions. However, further research is necessary to understand the potential of 6C CC chemokine 19 of C. striatus, particularly their regulatory ability on different cellular components in the defense system.

CsCCL17, a CC chemokine of Cynoglossus semilaevis, induces leukocyte trafficking and promotes immune defense against viral infection

CC chemokines are the largest subfamily of chemokines, which are important components of the innate immune system. To date, sequences of several CC chemokines have been identified in half-smooth tongue sole (Cynoglossus semilaevis); however, the activities and functions of these putative chemokines remain unknown. Herein, we characterized a CC chemokine, CsCCL17, from tongue sole, and examined its activity. CsCCL17 contains a 303 bp open reading frame, which encodes a polypeptide of 100 amino acids with a molecular mass of 12 kDa CsCCL17 is phylogenetically related to the CCL17/22 group of CC chemokines and possesses the typical arrangement of four cysteines and an SCCR motif found in known CC chemokines. Under normal physiological conditions, CsCCL17 expression was detected in spleen, liver, heart, gill, head kidney, muscle, brain, and intestine. When the fish were infected by bacterial and viral pathogens, CsCCL17 expression was significantly up-regulated in a time-dependent manner. Chemotactic analysis showed that recombinant CsCCL17 (rCsCCL17) induced migration of peripheral blood leukocytes. A mutagenesis study showed that when the two cysteine residues in the SCCR motif were replaced by serine, no apparent chemotactic activity was observed in the mutant protein rCsCCL17M. rCsCCL17 enhanced the resistance of tongue sole against viral infection, but rCsCCL17M lacked this antiviral effect. Taken together, these findings indicate that CsCCL17 is a functional CC chemokine with the ability to recruit leukocytes and enhance host immune defense in a manner that requires the conserved SCCR motif.

Antimicrobial response is increased in the testis of European sea bass, but not in gilthead seabream, upon nodavirus infection

Antimicrobial peptides (AMPs) have a crucial role in the fish innate immune response, being considered a fundamental component of the first line of defence against pathogens. Moreover, AMPs have not been studied in the fish gonad since this is used by some pathogens as a vehicle or a reservoir to be transmitted to the progeny, as occurs with nodavirus (VNNV), which shows vertical transmission through the gonad and/or gonadal fluids, but no study has looked into the gonad of infected fish. In this framework, we have characterized the antimicrobial response triggered by VNNV in the testis of European sea bass, a very susceptible species of the virus, and in the gilthead seabream, which acts as a reservoir, both in vivo and in vitro, and compared with that present in the serum and brain (target tissue of VNNV). First, our data show a great antiviral response in the brain of gilthead seabream and in the gonad of European sea bass. In addition, for the first time, our results demonstrate that the antimicrobial activities (complement, lysozyme and bactericidal) and the expression of AMP genes such as complement factor 3 (c3), lysozyme (lyz), hepcidin (hamp), dicentracin (dic), piscidin (pis) or β-defensin (bdef) in the gonad of both species are very different, but generally activated in the European sea bass, probably related with the differences of susceptibility upon VNNV infection, and even differs to the brain response. Furthermore, the in vitro data suggest that some AMPs are locally regulated playing a local immune response in the gonad, while others are more dependent of the systemic immune system. Data are discussed in the light to ascertain their potential role in viral clearance by the gonad to avoid vertical transmission.

Cloning and expression analysis of three novel CC chemokine genes from Japanese flounder (Paralichthys olivaceus)

Chemokines are small cytokines secreted by various cell types. They not only function in cell activation, differentiation and trafficking, but they also have influences on many biological processes. In this study, three novel CC chemokine genes Paol-SCYA105, 106 and 107 in Japanese flounder (Paralichthys olivaceus) were cloned and characterized. Paol-SCYA105 was mainly detected in gill, kidney and spleen, Paol-SCYA106 was detected in all tissues examined and Paol-SCYA107 was mainly detected in the spleen and kidney. Paol-SCYA105 and Paol-SCYA106 gene expressions peaked in kidney at day 3 after viral hemorrhagic septicemia virus infection and decreased at day 6, but Paol-SCYA106 still remained at a high level at day 6. Paol-SCYA107 gene expression was significantly up-regulated in kidney at day 6 after viral hemorrhagic septicemia virus infection. In response to infection by Gram-negative Edwardsiella tarda and Gram-positive Streptococcus iniae in kidney, only Paol-SCYA106 gene expression significantly increased. Together, these results indicate that these three novel CC chemokines are involved in the immune response against pathogen infections.

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.

The biofunction of orange-spotted grouper (Epinephelus coioides) CC chemokine ligand 4 (CCL4) in innate and adaptive immunity

CC chemokine (motif) ligand 4 (CCL4) is indispensable to the chemoattraction of macrophages, natural killer cells, and lymphocytes in mammals; however, it has only been cloned in a limited number of fish species and information related to its biofunction remains ambiguous with regard to teleosts. To explore the role of teleost CCL4, we first evaluated the mRNA expression of the Epinephelus coioides CCL4 (gCCL4) gene in various organs under LPS and poly (I:C) stimulated; secondary, we evaluated the immune-related genes expression of fish under the recombinant gCCL4 protein stimulated. Our results revealed an increase in the mRNA of gCCL4 in immune organs immediately following stimulation by poly (I:C); however, in LPS stimulated fish, the expression did not increase until nearly 24 h after induction. In biofunction assays, recombinant gCCL4 was found to induce chemotactic activity in the peripheral blood leukocytes of groupers and up-regulate the gene expressions of grouper TNFA1 (TNF-α1), TNFA2 (TNF-α2), IFNG (IFN-γ), MX, TBX21 (T-bet), CD8 (α and β chain). These findings indicate that grouper CCL4 attracts leukocytes, induces an inflammatory response, and drives lymphocyte differentiation into the Th1 pathway.

Identification and expression analysis of a CC chemokine from cobia (Rachycentron canadum)

Chemokines are small, secreted cytokine peptides known principally for their ability to induce migration and activation of leukocyte populations and regulate the immune response mechanisms. The cobia (Rachycentron canadum), a marine finfish species, has a great potential for net cage aquaculture in the South China Sea. We isolated and characterized a CC chemokine cDNA from cobia-designated RcCC2. Its cDNA is 783 bp in length and encodes a putative protein of 110 amino acids. Homology and phylogenetic analysis revealed that the RcCC2 gene, which contains four conserved cysteine residues, shares a high degree of similarity with other known CC chemokine sequences and is closest to the CCL19/21 clade. The mRNA of RcCC2 is expressed constitutively in all tested tissues, including gill, liver, muscle, spleen, kidney, head kidney, skin, brain, stomach, intestine and heart, but not blood, with the highest level of expression in gill and liver. The reverse transcription quantitative polymerase chain reaction was used to examine the expression of the RcCC2 gene in immune-related tissues, including head kidney, spleen and liver, following intraperitoneal injection of the viral mimic polyriboinosinic polyribocytidylic acid, formalin-killed Vibrio carchariae (bacterial vaccine) and phosphate-buffered saline as a control. RcCC2 gene expression was up-regulated differentially in head kidney, spleen and liver during 12 h after challenge. These results indicate that the RcCC2 gene is inducible and is involved in immune responses, suggesting RcCC2 has an important role in the early stage of viral and bacterial infections.

Molecular identification and expression analysis of the CC chemokine gene in rock bream (Oplegnathus fasciatus) and the biological activity of the recombinant protein

We identified the CC chemokine cDNA designated as RbCC1 (CC chemokine 1 in rock bream, Oplegnathus fasciatus), which was isolated using expressed sequence tag (EST) analysis of a lipopolysaccharide (LPS)-stimulated rock bream liver cDNA library. The full-length RbCC1 cDNA (850 bp) contained an open reading frame (ORF) of 366 bp encoding 122 amino acids. Results from our phylogenetic analysis demonstrated that the RbCC1 was closest relationship to the orange-spotted grouper and Mi-iyu croaker CC chemokines located within the fish CC chemokine group. RbCC1 was significantly expressed in the intestine, spleen, liver, and PBLs (peripheral blood leukocytes). Rock bream PBLs were stimulated with several mitogens, LPS and Con A/PMA which significantly induced the expression of RbCC1 mRNA in the PBLs. The RbCC1 mRNA expression in several tissues under conditions of bacterial and viral challenge was examined. The experimental challenge revealed that the kidney and spleen of fish infected with Streptococcus iniae showed the most significant increases in RbCC1 expression compared to the control. In the case of RSIV infection, the RbCC1 mRNA expression was markedly up-regulated in the liver. In this study, recombinant RbCC1 (approximately 53 kDa) was produced using an Escherichia coli expression system followed by purification. Subsequently, the addition of purified rRbCC1 was examined to investigate the impact on the proliferative and chemotactic activity on kidney leukocytes from rock bream. The results demonstrated that the rRbCC1 induces significant biological activity on kidney leukocyte proliferation and attraction at concentrations in the range of 10-300 μg/mL and suggests that rRbCC1 could be utilized as an immune-stimulant and/or molecular adjuvant to enhance the immune effects of vaccines.

Expression profile of immune-related genes in Lates calcarifer infected by Cryptocaryon irritans

Cryptocaryon irritans causes Cyptocaryonosis or white spot disease in a wide range of marine fish including Lates calcarifer (Asian seabass). However, the immune response of this fish to the parasite is still poorly understood. In this study, quantitative polymerase chain reaction (qPCR) was performed to assess the expression profile of immune-related genes in L. calcarifer infected by C. irritans. A total of 21 immune-related genes encoding various functions in the fish immune system were utilized for the qPCR analysis. The experiment was initiated with the infection of juvenile fish by exposure to theronts from 200 C. irritans cysts, and non-infected juvenile fish were used as controls. Spleen, liver, gills and kidney tissues were harvested at three days post-infection from control and infected fish. In addition, organs were also harvested on day-10 post-infection from fish that had been allowed to recover from day-4 up to day-10 post-infection. L. calcarifer exhibited pathological changes on day-3 post-infection with the characteristic presence of white spots on the entire fish body, excessive mucus production and formation of a flap over the fish eye. High quality total RNA was extracted from all tissues and qPCR was performed. The qPCR analysis on the cohort of 21 immune-related genes of the various organs harvested on day-3 post-infection demonstrated that most genes were induced significantly (p < 0.05) in all tissues, particularly liver (11/21 genes) and kidney (11/21). The expression profile demonstrated that induction of the MHC Class IIα gene was the highest compared to the other genes followed by serum amyloid A, CC chemokine and hepcidin-2 precursor genes. In fish that were allowed to recover from the C. irritans infection (10 days post-infection), expression of the immune-related genes was down-regulated to levels similar to the control fish. These results provide insights into the interaction between C. irritans and L. calcarifer and suggest that the innate immune system plays an important role in early defence against parasite infection allowing the fish to eventually recover from the infection.

Molecular cloning, characterization and expression analysis of a CC chemokine gene from miiuy croaker (Miichthys miiuy)

Chemokines are a family of structurally related chemotactic cytokines that regulate the migration of leukocytes, under both physiological and inflammatory conditions. A partial cDNA of CC chemokine gene designed as Mimi-CC3 was isolated from miiuy croaker (Miichthys miiuy) spleen cDNA library. Unknown 3' part of the cDNA was amplified by 3'-RACE. The complete cDNA of Mimi-CC3 contains an 89-nt 5'-UTR, a 303-nt open reading frame and a 441-nt 3'-UTR. Three exons and two introns were identified in Mimi-CC3. The deduced Mimi-CC3 protein sequences contain a 22 amino acids signal peptide and a 78 amino acids mature polypeptide, which possesses the typical arrangement of four cysteines as found in other known CC chemokines. It shares low amino acid sequence identities with most other fish and mammalian CC chemokines (less than 54.1 %), but shares very high identities with large yellow croaker CC chemokine (94.6 %). Phylogenetic analysis showed that Mimi-CC3 gene may have an orthologous relationship with mammalian/amphibian CCL25 gene. Tissue expression distributed analysis showed that Mimi-CC3 gene was constitutively expressed in all nine tissues examined, although at different levels. Upon stimulated with Vibrio anguillarum, the time-course analysis using a real-time PCR showed that Mimi-CC3 transcript in kidney and liver was obviously up-regulated and reached the peak levels, followed by a recovery. Mimi-CC3 expression in kidney was more strongly increased than in liver. However, down-regulation was observed in spleen. These results indicated that Mimi-CC3 plays important roles in miiuy croaker immune response as well as in homeostatic mechanisms.

Nodavirus infection induces a great innate cell-mediated cytotoxic activity in resistant, gilthead seabream, and susceptible, European sea bass, teleost fish

Viral nervous necrosis (VNN) virus produces great mortalities in fish having susceptible and reservoir species between the most important marine aquaculture species. Cell-mediated cytotoxicity (CMC) is considered, towards the interferon (IFN), the most important mechanism of the immune response to fight against viral infections but it has been very scarcely evaluated. We aimed to evaluate the effects of VNNV infection in the reservoir gilthead seabream (Sparus aurata) and susceptible European sea bass (Dicentrarchus labrax). Firstly, after experimental infection we found mortalities in the sea bass (55%) but no in the seabream. Moreover, VNN virus replicates in the brain of both species as it was reflected by the high up-regulation of the Mx gene expression. Interestingly, the head-kidney leucocyte cell-mediated cytotoxic activity was significantly increased in both species reaching highest activity at 7 days: 3.65- and 2.7-fold increase in seabream and sea bass, respectively. This is supported by the significant up-regulation of the non-specific cytotoxic cell receptor (NCCRP-1) in the two fish species. By contrast, phagocytosis was unaffected in both species. The respiratory burst was increased in seabream 7 days post-infection whilst in sea bass this activity was significantly decreased at days 7 and 15. Our results demonstrate the significance of the CMC activity in both gilthead seabream and European sea bass against nodavirus infections but further studies are still needed to understand the role of cytotoxic cells in the antiviral immune response and the mechanisms involved in either reservoir or susceptible fish species.

Transcriptomic response of skeletal muscle to lipopolysaccharide in the gilthead seabream (Sparus aurata)

The physiological consequences of the activation of the immune system in fish are not well understood. In particular, skeletal muscle, due to its essential role in locomotion and whole-animal energy homeostasis, is a potentially important target of inflammation. In this study, we have evaluated the in vivo effects of lipopolysaccharide (LPS) on the white and red skeletal muscle transcriptome of the gilthead seabream (Sparus aurata) by microarray analysis at 24 and 72 h after injection. In white muscle, the transcriptomic response was characterized by an up-regulation of genes involved in carbohydrate catabolism and protein synthesis at 24 h and a complete reversal of this pattern at 72 h. In red muscle, an up-regulation of genes involved in carbohydrate catabolism and protein synthesis was observed only at 72 h after LPS administration. Interestingly, both white and red muscles showed a similar consistent down-regulation of immune genes at 72 h post-injection. However, genes involved in muscle contraction showed a general up-regulation in response to LPS in both types of muscle. In summary, LPS administration causes muscle type-specific responses regarding the expression of genes involved in carbohydrate and protein metabolism and a common decreased expression of immune genes in skeletal muscle, concomitant with increased expression of genes for contractile elements. Our results evidence a robust and tissue-specific transcriptomic response of the skeletal muscle to an acute inflammatory challenge.

Identification of a cobia (Rachycentron canadum) CC chemokine gene and its involvement in the inflammatory response

The chemokines regulate immune cell migration under inflammatory and physiological conditions. We investigated a CC chemokine gene (RcCC1) from cobia (Rachycentron canadum). The full-length RcCC1 cDNA is comprised 673 nucleotides and encodes a four-cysteine arrangement 99-amino-acid protein typical of known CC chemokines. The genomic DNA of RcCC1 consists of three exons and two introns. Phylogenetic analysis showed that RcCC1 was closest to the MIP group of CC chemokines. Quantitative real-time RT-PCR (qRT-PCR) analysis revealed RcCC1 was constitutively expressed in all tissues examined, with relative strong expression in gill, blood, kidney, spleen, and head kidney. The RcCC1 transcripts in the head kidney, spleen, and liver were quickly up-regulated after stimulation with formalin-inactivated Vibrio carchariae (bacterial vaccine) or polyriboinosinic polyribocytidylic acid (poly I:C). These results indicate RcCC1 not only plays a role in homeostasis, but also may be involved in inflammatory responses to bacterial and viral infection.

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.

An inflammatory CC chemokine of Cynoglossus semilaevis is involved in immune defense against bacterial infection

Chemokines are a family of small cytokines that regulate leukocyte migration. Based on the arrangement of the first two cysteine residues, chemokines are classified into four groups called CXC(α), CC(β), C, and CX(3)C. In this study, we identified a CC chemokine, CsCCK1, from half-smooth tongue sole (Cynoglossus semilaevis) and analyzed its biological activity. The deduced amino acid sequence of CsCCK1 contains 111 amino acid residues and is phylogenetically belonging to the CCL19/21/25 group of CC chemokines. CsCCK1 possesses a DCCL motif that is highly conserved among CC chemokines. Quantitative real time RT-PCR analysis showed that the expression of CsCCK1 was relatively abundant in immune organs under normal physiological conditions and was upregulated by experimental infection of a bacterial pathogen. Purified recombinant CsCCK1 (rCsCCK1) induced chemotaxis in peripheral blood leukocytes (PBL) of both tongue sole and turbot (Scophthalmus maximus) in a dose-dependent manner. Mutation of the CC residues in the DCCL motif by serine substitution completely abolished the biological activity of rCsCCK1. When rCsCCK1, but not the mutant protein, was added to the cell culture of PBL, it enhanced cellular resistance against intracellular bacterial infection. Taken together, these results indicate that CsCCK1 is a functional CC chemokine whose biological activity depends on the DCCL motif and that CsCCK1 plays a role in host immune defense against bacterial infection.

Molecular and functional characterization of the gilthead seabream β-defensin demonstrate its chemotactic and antimicrobial activity

Antimicrobial peptides (AMPs) are important mediators of the innate immune response against bacteria and viruses. We have found a β-defensin (BD) gene searching the expressed sequence tags (ESTs) of the teleost fish gilthead seabream (Sparus aurata). The clone contains an open reading frame of 201 bp mRNA that encodes a putative seabream β-defensin (saBD) propeptide of 66 amino acids containing the six conserved cysteines as the main signature of this AMP. The phylogenetic tree shows that saBD, and its fish orthologues, are closely related to the human BD-4. Transcripts of the saBD gene were mainly detected by real-time PCR in the skin, peritoneal leucocytes and head-kidney but scarcely expressed in the peripheral blood. Interestingly, head-kidney leucocytes incubation with synthetic unmethylated CpG oligodeoxynucleotides and bacterial DNA up-regulated the saBD gene expression. Recombinant protein (saBD-V5-His) was expressed in the HEK293 cell line and its functional activity determined. First, seabream head-kidney leucocytes showed chemotactic activity towards supernatants containing saBD-V5-His whilst failed to do so to human recombinant BD-1 y BD-4. Moreover, both cell lysates and supernatants containing saBD-V5-His showed strong antimicrobial activity against Vibrio anguillarum (a seabream pathogenic bacterium) and Bacillus subtilis whilst little on other fish pathogens such as Vibrio harvey and Photobacterium damselae. Further studies will elucidate the existence of other BD genes and their implications on the seabream defense against bacteria and virus.